POPULATION DYNAMIC MODELING OF THE CORKSCREW SEA ANEMONE 
BARTHOLOMEA ANULATA ON CARIBEAN CORAL REFS 
 
 
Except where reference is made to the work of others, the work described in this 
thesis is my own or was done in collaboration with my advisory commite. 
This thesis does not include proprietary or clasified information. 
 
!!!!!! 
Michael W. Nelsen 
 
Certificate of approval: 
 
!!!!!!    !!!!!! 
Stephen Kempf      Nanete Chadwick, Chair 
Associate Profesor      Associate Profesor 
Biological Sciences      Biological Sciences 
 
 
!!!!!!    !!!!!! 
Georg Hetzer       George T. Flowers 
Profesor       Dean 
Mathematics and Statistics     Graduate School 
 
 
 
 
 
 
 
 
 
 
POPULATION DYNAMIC MODELING OF THE CORKSCREW SEA ANEMONE 
BARTHOLOMEA ANULATA ON CARIBEAN CORAL REFS 
 
 
Michael W. Nelsen 
 
A Thesis 
Submited to 
the Graduate Faculty of 
Auburn University 
in Partial Fulfilments of the 
Requirements for the 
Degre of 
Master of Science 
 
 
 
Auburn, AL 
December 19, 2008 
ii 
 
 
 
 
 
POPULATION DYNAMICS MODELING OF THE CORKSCREW SEA ANEMONE 
BARTHOLOMEA ANULATA ON CARIBEAN CORAL REFS 
 
 
Michael W. Nelsen 
 
 
Permision is granted to Auburn University to make copies of this disertation at its 
discretion, upon request of individuals or institutions at their expense. 
The author reserves al publication rights. 
 
 
 
 
 
 
 
!!!!!! 
Signature of Author 
 
 
 
 
!!!!!! 
Date of Graduation 
 
 
 
 
 
iv 
 
 
 
VITA 
 
Michael W. Nelsen, son of Gary Nelsen and Sheila Gardineer born August 22, 
1983, in Fremont, Michigan. He graduated with a Bachelor of Arts degre in Biology 
and Mathematics in 2005 from Hope College in Holland, MI.  In the Fal of 2006 he 
entered the Graduate School in the Department of Biological Sciences where he joined 
the laboratory of Dr. Nanete E. Chadwick and is currently pursuing a Masters degre.  
 
v 
 
 
 
 
 
THESIS ABSTRACT 
 
POPULATION DYNAMICS MODELING OF THE CORKSCREW SEA ANEMONE 
BARTHOLOMEA ANULATA ON CARIBEAN CORAL REFS 
Michael W. Nelsen 
Master of Science, December 19, 2008 
(B. A., Hope College, 2005) 
 
107 Typed Pages 
 
Directed by Nanete E. Chadwick 
The corkscrew anemone Bartholomea anulata is a large, common sea anemone on 
Caribean coral reefs. The holobiont of B. anulata, endosymbiotic microalgae (zooxanthellae), 
and ectosymbiotic cleaner shrimps may have positive cascade effects in coral reef communities 
by serving as fish cleaning stations. Thus, colection of B. anulata for the ornamental aquarium 
trade may indirectly impact reef fish diversity, yet this fishery is largely uncontroled and has 
drastically reduced the abundance of these sea anemones in some parts of the Caribean. The 
dynamics of 2 unfished populations of B. anulata in the US Virgin Islands were modeled here, 
to determine how they vary spatially (between habitats) and temporally (among 4 seasons). 
Seven types of demographic models were used to project future population size and structure at 
each of the 2 study sites.  
Population dynamics differed significantly between the 2 examined study locations, with 
higher mortality at the outer reef site (Flat Cay) and higher rates of transition between size-
classes (growth and shrinkage) at the iner reef site (Brewers Bay). There was no significant 
vi 
difference in the rate of total recruitment between these 2 populations, but both the number of 
recruits per m
2
 and recruits per resident anemone per m
2
 were significantly higher at Brewers 
Bay, while the number of recruits per resident anemone was significantly higher at Flat Cay. 
Light intensity, sediment grain size, percent stony coral cover, and relative water motion all were 
significantly greater at the outer site of Flat Cay than at the iner protected site in Brewers Bay. 
These differences in site characteristics may influence the demography of B. anulata at each 
site, in particular rates of anemone growth and mortality.  
Matrix models based on current population trends projected the survival of these 
populations at both sites. Closed population models for both sites projected exponential growth 
and population sizes much larger than the potential carrying capacities of the sites. In contrast, 
the open and semi-open models projected stabilization of the anemone populations, though the 
equilibrium sizes of the populations varied among models. Elasticity analyses of the matrix 
models indicated that the smallest individuals contributed the most to population growth, and 
sugest a need for establishing a minimum body size for the colection for these organisms. 
When outside recruitment was removed from the open and semi-open models, anemone 
populations were projected to plummet to zero within about 3 years, revealing the importance of 
outside recruitment for population growth and stability. Thus, unfished marine preserves near 
fished areas of these anemones may be important as sources of outside recruitment. It is 
concluded that the establishment of unfished marine preserves adjacent to fished populations, and 
a minimum body size for colection, are recommended for the development of a sustainable 
fishery on this giant sea anemone on Caribean coral reefs. 
 
 
 
vii 
 
 
 
ACKNOWLEDGEMENTS 
 
First and foremost I would like to expres my appreciation and thanks to my 
advisor, Dr. Nanete E. Chadwick, for her guidance and encouragement throughout my 
studies here at Auburn University. My thesis would not be possible without her advice 
and undying devotion to this research. Secondly, I would like to thank my other 
commite members Dr. Stephen Kempf and Dr. Georg Hetzer for their helpful 
discussions and constructive suggestions to my thesis. I would like to thank my beautiful 
fianc?e Stefanie Haba for al the help and support throughout my time at Auburn, 
without her wilingnes to listen and ability to deal with my antics I do not know if I 
could have made it. I would also like to thank my current lab mate Kathlen Morrow for 
her meaningful discussions and help during my studies. I would also like to thank al of 
my asociates at The University of the Virgin Islands who helped collect data and 
showed me around the island, especialy Dr. Stephen Ratchford who let me slep at his 
house on many occasions. I would also like to extend my thanks to the many friends I 
have made during this stage of my life. I want to especialy expres my gratitude to my 
parents Gary Nelsen and Sheila Gardineer and my brothers David and Steven for always 
supporting me throughout my life. And last, but certainly not least, I would like to thank 
the Department of Biological Sciences and the Virgin Islands EPSCOR and Puerto Rico 
Sea Grant for their monetary support. 
viii 
 
 
 
 
 
Style manual used:  
Auburn University Guide To Preparing And Submision Of Theses and Disertations 
Computer software used:  
Microsoft Word 
Microsoft Excel 
Microsoft Powerpoint 
Matlab v. 7.2.0.232(R2006a) 
SAS v. 9.1 
 
ix 
 
 
 
 
 
TABLE OF CONTENTS 
LIST OF TABLES.........................................................................................................xi 
LIST OF FIGURES.....................................................................................................xii 
CHAPTER I: INTRODUCTION.....................................................................................1 
  History and Applications of Population Modeling..............................................1 
  Matrix Theory for Population Models................................................................3 
  Population Ecology of Caribbean Sea Anemones...............................................4 
 RESEARCH OBJECTIVES.......................................................................................7 
 LITERATURE CITED.............................................................................................10 
CHAPTER I: POPULATION DYNAMICS OF THE CORKSCREW ANEMONE 
BARTHOLOMEA NULATA ON CARIBEAN CORAL REFS19 
INTRODUCTION...................................................................................................19 
METHODS..............................................................................................................22 
Study Site Characteristics................................................................................22 
Sea Anemone Population Dynamics................................................................25 
Data Analysis..................................................................................................26 
RESULTS................................................................................................................28 
Study Site Characteristics................................................................................28 
Sea Anemone Population Dynamics................................................................29 
DISCUSSION..........................................................................................................33 
x 
LITERATURE CITED............................................................................................41 
CHAPTER II: STAGE-BASED MODELING OF POPULATION DYNAMICS OF 
THE POPULATION DYNAMICS IN THE CORKSCREW 
ANEMONE BARTHOLOMEA ANULATA................................59 
INTRODUCTION...................................................................................................59 
METHODS..............................................................................................................62 
Collection of Population Data..........................................................................62 
Population Modeling.......................................................................................62 
Modeling of Reproduction...............................................................................63 
Data Analysis..................................................................................................68 
RESULTS................................................................................................................68 
DISCUSSION..........................................................................................................74 
LITERATURE CITED............................................................................................79 
 
xi 
 
 
 
 
 
LIST OF TABLES 
 
Table 2.1 Statistical results of 2-tailed t-tests on diferences in physical characteristics 
between 2 coral ref sites (Brewers Bay and Flat Cay). Sediment size, 
iradiance at peak hours, iradiance during the entire daylight period, 
percent change in clod card mas, absolute change in clod card mas, and 
percent stony coral cover al were significantly greater at Flat Cay than at 
Brewers Bay, while there was no significant diference in sedimentation 
rate between the 2 sites..............................................................................48 
Table 2.2 Variation among seasons and sites in the percent of anemones that either 
grew, shrank, remained in the same size clas, or died (based on TCSA)...49 
Table 2.3 Variation among size clases and sites in the mean percent of 
individuals (? S.D.) that either grew, shrank, remained in the same size 
clas, or died (based on TCSA, N=4 seasons, NA= not applicable)............49 
Table 2.4 Variation in rates of recruitment of new anemones between 2 coral ref 
sites. Data are presented as mean percent of individuals ? 1 standard 
deviation. N=4 seasons examined..............................................................50 
Table 3.1 Transition matrices for the sea anemone Bartholomea annulata in 3 types of 
population models (A, B, C). The sum of a column is equal to the survival 
xii 
of that size-clas of anemones. (G) represents growth, (S) represents 
shrinkage, and (L) represents remaining in the same size-clas (stasis)......84 
Table 3.2 Variation in A. dominant eigenvalues (finite population growth rate, !), 
B. Time in years to reach stable size structure, and C. time until 
populations reduce to zero without outside recruitment, for populations 
of the sea anemone Bartholomea annulata among 3 types of population 
matrices (closed, open, and semi-open) at 2 coral ref sites (Brewers 
Bay and Flat Cay). Dominant eigenvalues >1 represent population 
growth, and <1 represent population shrinkage..........................................85 
Table 3.3 Proportion of individuals of the sea anemone Bartholomea annulata in 
each size-clas after projected stable-size structure has been reached. 
Actual observed population size-structure during the March 2007 census 
also is given for comparison......................................................................86 
Table 3.4 Elasticity values of each size clas of individuals (columns) in 
populations of the sea anemone Bartholomea annulata at 2 coral ref 
sites (Brewers Bay and Flat Cay). Bold numbers represent the greatest 
elasticity values in each table. A. Closed populations, bold represents 
elasticities >0.5. B. Open populations, bold represents elasticities 
>0.01. C. Semi-open populations, bold represents elasticities >0.1......87, 88 
Table 3.5 Thre types of transition matrices (closed, open, semi-open) used to 
construct population models for the sea anemone Bartholomea annulata 
at each of 2 coral ref sites (Brewers Bay and Flat Cay).............................88 
xiii 
 
 
 
 
LIST OF FIGURES 
 
Figure 1.1 Example of an age-based life cycle graph. Arrows pointing to the right 
represent organisms growing older by one time period (g), while left-
pointing arows represent reproduction/recruitment (f). In this example, the 
organisms either grow older or die during each period (modified after 
Hughes 1984)...........................................................................................16 
Figure 1.2 Size-based life cycle graph for the corkscrew anemone Bartholomea 
annulata. Arrows pointing to the right represent B. annulata growing to 
a larger size-clas (g), left-pointing arows represent B. annulata 
shrinking to a smaler size-clas and/or reproducing (s), and looping 
arows represent B. annulata remaining in the same size-clas (stasis, L).  
In this example, individuals of B. annulata either grow, shrink, remain in 
the same size-clas, or die (modified after Hughes 1984)...........................17 
Figure 1.3 Number individuals of the corkscrew anemone B. annulata collected 
commercialy per year in the state of Florida during 1990-2007. In 2005, 
the law changed to require individuals to purchase permits from collectors 
that currently posses them (data obtained from the Florida Fish and 
Wildlife Conservation Commision)..........................................................18 
xiv 
Figure 2.1 Maps showing 2 coral ref sites examined for sea anemone population 
dynamics near the island of St. Thomas, USVI. Site #1 Brewers Bay, is 200 
m from island, and site #2 Flat Cay is 2.2 km from island..........................53 
Figure 2.2 Maps from Dec. 2007 showing locations of tagged sea anemones along the 
ref-sand margin at: A. the Brewers Bay study site. B. the Flat Cay study 
site. Numbers refer to the tag number of each anemone......................54, 55 
Figure 2.3 A. Percent of anemones oriented horizontaly, verticaly, and midway 
between horizontaly/verticaly at Brewers Bay and Flat Cay. At both 
locations, most of anemones were oriented verticaly. Data are 
presented as means ? 95% CI, N=104 anemones examined at Brewers 
Bay and N=52 anemones examined at Flat Cay. B. Percent of 
anemones that were located in each microhabitat. Most anemones were 
found at the rock/sand interface at both locations. Data are presented as 
means ? 95% CI, N=102 anemones examined at Brewers Bay and N=52 
anemones examined at Flat Cay.................................................................56 
Figure 2.4 Population size-structure of the sea anemone Bartholomea annulata at 2 
coral ref sites (Brewers Bay N=108 and Flat Cay N=53). Sea anemones 
were significantly larger, and populations size was significantly greater at 
Brewers Bay than at Flat Cay (se text for details).....................................57 
Figure 2.5 A. Dynamic survival curves for Brewers Bay and Flat Cay, from observed 
disappearance of tagged sea anemones at each site over one year of study. 
Curves show that anemones are most likely to survive for one year at 
Brewers Bay (Brewers Bay, y=1.007e
-.17x
 R
2
=.999, Flat Cay, y=1.027e
-.183x
 
xv 
R
2
=.996). B. Static survival curves for Brewers Bay and Flat Cay, 
constructed from the observed population structure of sea anemones at each 
site during March 2007. Static survival curves show that anemones are 
more likely to grow larger at Brewers Bay than at Flat Cay.......................58 
Figure 3.1 30-year projections for 3 types of size-based matrix models of populations 
of the sea anemone Bartholomea annulata at 2 coral ref sites (Brewers Bay 
and Flat Cay): A. Closed models for both ref sites. Anemone populations 
are projected to grow much larger than carying capacity would alow. B. 
Open models at Brewers Bay. C. Semi-open models at Brewers Bay. D. 
Open models at Flat Cay. E. Semi-open models at Flat Cay. For al open 
and semi-open models, population sizes projected by the models that use 
actual recruitment and average values are slightly larger than current levels, 
while the maximal model projects anemone populations to be smaler. 
Average and maximal models are shown as means +/- SEM of N=30 
replicates.......................................................................................90, 91, 92 
 
 
 
 
1 
CHAPTER I 
 
INTRODUCTION 
 
 
History and Applications of Population Modeling 
 
Over the past sixty years, mathematics has become an important tool in the management 
of biological systems. In 1945, Patrick Holt Leslie developed a method to use matrices to 
represent a population of organisms if the ages of individuals in the population are 
known. This method has been applied to a variety of organisms ranging from black 
rhinos and eagles to cheetahs and everything in between (Crooks et al. 1998, Cromsigt et 
al. 2002, Katzner et al. 2006). Although Leslie was one of the earliest and most 
influential mathematicians to use matrices to model biological systems, he was not the 
first to use reproduction and survival rates to model population growth (Caswel 2001). 
In 1895, Edwin Cannan used these vital rates to analyze ?The cesation of the growth of 
population in England and Wales?, and he is credited with being the first to use vital rates 
in population modeling (Caswel 2001). 
 
 
2 
 The first major variation on Leslie?s model was introduced in 1965 by Lenard 
Lefkovitch. Lefkovitch took Leslie?s model and modified it so that the matrix was no 
longer divided into age classes of equal length, but into stages that did not have to be 
equal in length (Lefkovitch 1965). This modification allowed for more accurate 
modeling of organisms, such as beetles, where life stages such as pupae and larvae 
describe the biology of the organism better than the age does. 
 The demography of marine organisms typically is modeled using either stage-
based or size-based matrices for several reasons, the most prominent of which is that 
often it is dificult to determine the ages of individuals from their appearance. Some 
marine invertebrates may shrink or fragment and thus decrease in size as they age 
(Hughes 1984, Cropper and DiResta 1999, Hughes and Tanner 2000, and Cropper et al. 
2001), so it is easier to classify them by stage/size rather than age. Secondly, it has been 
dificult to perform long-term studies on organisms underwater. It is much easier to 
observe and collect data on birds everyday with binoculars than to measure the height of 
gorgonian soft corals on a daily basis, using SCUBA. For example, Gotelli (1991) 
mises several months of data collection on a gorgonian population because the water 
was too cold to dive in for long periods of time. Due in part to these limitations of 
working on marine organisms, matrix modeling has been applied to a variety of marine 
invertebrates, including lobsters in Maine (Incze et al. 2006), soft-shell clams in 
Massachusetts (Ripley and Caswell 2006), and corals during recovery from disturbances 
on tropical reefs in the Florida Keys (Lirman and Miler 2003).  
 The above studies have used matrix modeling to manage populations of 
organisms. Another use of matrix models is in the development of marine 
 
3 
preserves/sanctuaries, which have become popular tools in conservation planning. 
Gerber and Heppell (2004) showed that matrix modeling could improve the efficacy of 
marine sanctuaries. Currently, marine sanctuaries are designed in locations that provide 
the most protection for adult individuals. Mathematical modeling of the species that the 
sanctuaries are designed to protect can reveal the crucial life stages that require the most 
protection. Then the sanctuaries can be more properly designed so that optimal 
population growth is obtained. For example, in many marine species the juveniles and 
adults live in diferent habitats (Sebens 1981, Mumby and Hastings 2008), thus modeling 
may show that the efficacy of marine preserves may be greater near nursery habitats 
where juveniles occur, rather than in the habitats with contain most adults. Another 
benefit is that by using matrix models, populations can be better managed with less 
overall cost (Rose and Cowan 2003). Another advantage of modeling is that it allows for 
better planning. A model can project the size of future populations of target organisms, 
allowing for multi-year planning versus plans for only a single year. 
 
Matrix Theory for Population Models 
 
 The matrix population model described by Leslie (1945, 1948) may be expressed 
as b
t+1
=A*b
t
 (Eq. 1.1) where A is the s x s transition matrix, b
t
 is the s x 1 population 
vector at time t, and b
t+1
 is the population vector at time t+1. The elements in vector b
t
 
are the number of individuals in each stage/age clas in the population at time t 
(t=0,1,2,3,?, n). How the elements in A are arranged wil depend on whether an age or 
stage based model is used. If an age-based model is used, then the top row and the sub-
 
4 
diagonal wil be the only elements of the matrix used (Fig. 1.1). If A is a stage-based 
matrix, then it is possible that any and/or every element in the matrix could be used (Fig. 
1.2). The top row elements can be diferent from the rest of the values in the matrix. 
These elements can represent sexual reproduction, asexual reproduction, and new 
recruitment into the population combined with shrinkage of larger individuals. They can 
be greater than one (depending on the population being studied), whereas none of the 
other elements can be. Fecundity may be greater than one because it represents offspring 
produced from organisms currently in the population while the other elements represent a 
proportion of the individuals that transition from one stage/size to another. A is typically 
known as a transition matrix because the probabilities therein reveal whether or not an 
individual in a given class wil remain in the same class or transition forward or 
backward. In age-based models, the transition is only from one age to the next, whereas 
stage-based models allow for movement of more than one stage in either direction, as 
well as for individuals remaining in the same stage. The vector n(t+1) is the result of 
multiplying A*n(t). This vector gives the composition of the population after it has 
transitioned from time t to time (t+1). Matrix modeling is a useful technique for the 
projection of future population size but it has yet to be used for tropical sea anemones, 
especially those in the Caribbean Sea. 
 
Population Ecology of Caribean Sea Anemones 
 
The rosetip anemone Condylactis gigantea and the corkscrew anemone 
Bartholomea annulata (Cnidaria: Anthozoa: Actiniaria) are the largest and most common 
 
5 
sea anemones in the Caribbean Sea, and yet litle information exists on the biology of 
either species (Colin 1978, Kaplan 1982, Sefton & Webster 1986). This lack of 
information precludes a scientific basis for management of commercial fishing of these 
animals. Collection of sea anemones for ornamental aquarium use is a $6 milion per 
year industry in Florida alone, with 11.8 milion individuals of C. gigantea collected 
commercially, not including anemones taken by non-commercial collectors (Chiappone 
et al. 2001). Commercial fishing data for B. annulata show that the number collected in 
the state of Florida has sharply declined over the past decade, indicating a general decline 
in anemone populations (Fig. 1.3). In addition, individuals of B. annulata are one of the 
most common invertebrates collected for the aquarium trade in Puerto Rico. B. annulata 
is number 7 on the list of invertebrates collected, with 650 individuals collected by one 
collector in the first six months of 2002 (LeGore et al. 2005). Currently, no data exist on 
how these rates of fishing affect these sea anemone populations, or on the extent to which 
the fishery is sustainable but Chiappone et al. (2001) suggest that because of the 
distributional patterns of these anemones, the populations in Florida are unlikely to 
recover from this intense fishing pressure.  
 Governmental agencies that regulate collecting have assumed that both C. 
gigantea and B. annulata have high rates of population turnover, and thus that intensive 
fishing may not be a problem because many offspring are produced each year (Chiappone 
et al. 2001). These assumptions are not supported by the limited evidence available on 
the reproduction of these species. Jennison (1981) showed that individuals of C. 
gigantea are large, long-lived, and produce small numbers of large eggs. Those of B. 
annulata produce a larger number of eggs, but their planktotrophic planulae likely are 
 
6 
susceptible to high rates of mortality due to starvation and predation during the drifting 
planktonic phase. As populations of these anemones decrease due to over-fishing, other 
problems can arise. Fertilization of gametes in both C. gigantea and B. annulata is 
external (Jennison 1981), thus as population size decreases, so does the concentration of 
their gametes in seawater and the probability that external fertilization wil be successful 
(Levitan et al. 1992, 2004). 
 Individuals of C. gigantea and B. annulata serve as hosts to a diverse assemblage 
of ectosymbiotic fish and crustacean associates (Mahnken 1972). Obligate associates of 
particular importance are the cleaner shrimps. Several species of Periclimenes and one of 
Thor are known to be obligate shrimp mutualists with these anemones (Mahnken 1972, 
Nizinski 1989, Crawford 1992, Gwaltney and Brooks 1993). The anemones provide 
protection from predation for the shrimps, and the shrimps in some cases provide 
nutrients to the host anemones (Spotte 1996). Together, the holobiont of anemone host 
and shrimp associates fils an important niche in coral reef ecosystems (Nizinski 1989, 
Fautin et al. 1995).  
 The cleaner-shrimp Periclimenes pedersoni uses both species of giant anemone 
(C. gigantea and B. annulata) as base stations, and cleans external parasites from fish that 
inhabit the coral reef (Mahnken 1972, Nizinski 1989, Crawford 1992, Gwaltney and 
Brooks 1993, Becker and Grutter 2004). Thus, anemone-based cleaning stations may 
indirectly affect multiple trophic levels on the reef through positive effects on large 
carnivorous reef fish. Bshary (2003) conducted a long-term study that revealed how 
cleaners significantly impact coral reef communities. Four months after the removal of 
cleaners, the species diversity of client fish (small groupers [Serranidae], surgeon fish 
 
7 
[Acanthuridae], squirelfish [Holocentridae], damselfish [Pomacentridae], wrasses 
[Labridae], dottybacks [Pseudochromidae], and cardinalfish [Apogonidae]) decreased by 
18% after natural loss of cleaners and 24% after artificial cleaner removal, and did not 
return to normal levels for at least twenty months. Bshary also showed that the addition 
of cleaners to a reef can augment fish species diversity both through attraction and 
imigration of fishes, and through enhanced survival and retention of cleaned fish. After 
two to four weeks on reefs where cleaners had naturally arrived, there was a 34% 
increase in fish species diversity, and on reefs where cleaners were experimentally added 
there was a 42% increase in diversity. Increases in fish diversity due to the presence of 
cleaners can have a positive feedback effect on host sea anemones as well as on other 
zooxanthellate organisms in the community. This is because as the number of client fish 
increase, so does the amount of nitrogen waste excreted by these fish in the vicinity of the 
sea anemones, potentially providing enhanced nutrients to both the sea anemones and to 
nearby stony corals (Meyer and Schultz 1985a and b, Fautin et al. 1995, Spotte 1996, 
Porat and Chadwick-Furman 2005, Roopin et al. 2008). Over-fishing of the anemones C. 
gigantea and B. annulata thus potentially can cascade into major reductions of fish 
populations through the above indirect effects. 
 
Research Objectives 
 
 The following research questions on populations of B. annulata are addressed in 
this thesis: (1) How do patterns of recruitment, changes in body size (growth/shrinkage), 
and mortality vary between two examined populations of this sea anemone? (Chapter I), 
 
8 
(2) What do population models predict about the crucial life stages, recovery times 
following disturbance, and minimum population size for recovery of this sea anemone? 
(Chapter II), and (3) What changes need to be made in management of this species, to 
support a sustainable fishery in the Caribbean? (Chapter II). 
 The methods employed in this study involved, firstly, collection of field data. The 
dynamics and stability of populations of the sea anemone B. annulata were examined, 
and patterns of recruitment, mortality, growth, and shrinkage of individuals were 
monitored every 3 months over a 1-year period (Mar. 07, June 07, Sept. 07, Dec. 07, and 
Mar. 08). B. annulata was the focus of this thesis, because populations of the other giant 
anemone in the Caribbean, C. gigantea, were too low at my study sites to use them for 
modeling. Secondly, the collected field data were used to create a stochastic population 
model in which a transition matrix, based on the probability of individuals transitioning 
among size classes, was used to make projections about future population size. Hughes 
(1984) created a general model for cnidarian population dynamics based on individual 
size rather than age, which was the basis for the models created in this study. In B. 
annulata, small individuals may be budded clonemates of older individuals produced 
through asexual replication, in addition to being new recruits from sexually-produced 
planula larvae. Because of this, an age-based model is not appropriate for this species 
(Jennison 1981).  
 The population projection model also was used to project the future condition and 
stability of populations of B. annulata at present rates of change at my field sites. I 
examined two unfished populations at St. Thomas, United States Virgin Islands, as a 
baseline to determine which vital rate was most crucial to maintain population growth, or 
 
9 
which stage needed the most protection in order to enhance population recovery. 
Currently, commercial vessels are allowed to collect up to 400 sea anemones per day in 
some areas of the Caribbean, and declining populations indicate that this number may 
need to be drastically reduced (Chiappone et al. 2001). 
 
10 
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Becker, J.H., and Gruter, A.S. 2004. Cleaner shrimp do clean. Coral Reefs 23(4): 515-
520. 
Bshary, R. 2003. The cleaner wrasse, Labroides dimidiatus, is a key organism for reef 
fish diversity at Ras Mohammed National Park, Egypt. Journal of Animal Ecology 
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11 
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Cropper, W.P. JR., Lirman, D., Tosini, S.C., DiResta, D., Juo, J., and Wang, J. 2001. 
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Gwaltney, C.L. and Brooks, W.R. 1994. Host specificity of the anemoneshrimps 
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93. 
Hughes, T.P. 1984. Population dynamics based on the individual size rather than age: A 
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13 
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14 
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15 
Figure Legends 
 
Fig. 1.1. Example of an age-based life cycle graph. Arrows pointing to the right 
represent organisms growing older by one time period (g), while left-pointing arrows 
represent reproduction/recruitment (f). In this example, the organisms either grow older 
or die during each period (modified after Hughes 1984). 
 
Fig. 1.2. Size-based life cycle graph for the corkscrew anemone Bartholomea annulata. 
Arrows pointing to the right represent B. annulata growing to a larger size-class (g), left-
pointing arrows represent B. annulata shrinking to a smaller size-class and/or 
reproducing (s), and looping arrows represent B. annulata remaining in the same size-
class (stasis, L). In this example, individuals of B. annulata either grow, shrink, remain 
in the same size-class, or die (modified after Hughes 1984). 
 
Fig. 1.3. Number individuals of the corkscrew anemone B. annulata collected 
commercially per year in the state of Florida during 1990-2007. In 2005, the law 
changed to require individuals to purchase permits from collectors that currently possess 
them (data obtained from the Florida Fish and Wildlife Conservation Commision).
 
16 
 
Fig. 1.1. 
 
17 
 Fig. 1.2. 
 
18 
 
Fig. 1.3. 
19 
CHAPTER I 
 
POPULATION DYNAMICS OF THE CORKSCREW ANEMONE 
BARTHOLOMEA NNULATA ON CARIBEAN CORAL REEFS 
 
Introduction 
 
 Giant sea anemones may be important members of coral ref communities due to 
their hosting of many species of obligate and facultative fish and crustacean symbionts 
(Fautin and Allen 1997, Bauer 2004). Large Caribbean sea anemones such as 
Bartholomea annulata and Condylactis gigantea serve as important symbiotic hosts to a 
variety of crustaceans, including the cleanershrimps Periclemenes pedersonii (Gwaltney 
and Brooks 1994) and P. yucatanicus (Gwaltney and Brooks 1994), and several other 
types of shrimp asociates (Knowlton and Keler 1983, Knowlton and Keler 1985, 
Nizinski 1989, Crawford 1992). While most aspects of these symbioses are not fully 
understood, it is known that some of the crustaceans supply nitrogen to the anemone 
hosts (Spotte 1996, Lipschultz 2001). The holobiont of host anemone, crustacean 
ectosymbionts, and microalgal endosymbiont (zooxanthelae) plays an important role in 
the ref community, because it serves as a cleaning station for large ref fish (Bunkley-
Wiliams and Wiliams 1998, Becker 2004). 
20 
 
 Through positive cascade effects, fish-cleaning stations can influence coral reef 
community structure and coral-algal competition. Both Grutter et al. (2003) and Bshary 
(2003) showed that the removal of the cleaner wrase Labroides dimidiatus causes a 
decrease in the diversity of both permanent and visiting reef fishes, and that the addition 
of this cleaner wrasse causes an increase in the fish diversity. Though this type of study 
has not been conducted with cleaner shrimps, it is likely that similar results would occur 
because changes in the cleaning process itself appear to drive reef fish diversity, rather 
than the type of cleaner involved. The presence of large fishes, especially visitors to the 
reef, influences coral-algal competition, as many migrating reef fish graze on macroalgae 
(McCook 2001). Thus, a decrease in the number of fishes or other grazers can result in a 
phase-shift to an alternate stable state in which algae rather than stony corals dominate 
reef areas (Hughes et al. 1987, Tkachenko 2007).  
 Understanding of population dynamics is important in order to gauge how 
environmental conditions impact populations of coral reef organisms (Chatzinkolaou and 
Richardson 2008). Sea anemones occur in a variety of reef habitats, and their patterns of 
growth, shrinkage, mortality, and recruitment/reproduction vary with the physical 
conditions in each habitat. Sebens (1981) showed that juveniles and adults of the 
temperate anemone Anthopleura xanthogrammica (Brandt) preferred diferent habitats, 
and that when juveniles reached a threshold body size, they moved to the preferred adult 
habitat.  
 No published information exists concerning the population dynamics of the 
corkscrew anemone Bartholomea annulata, yet individuals of this species are common 
21 
on Caribbean coral reefs. In Florida, fishing of B. annulata for the ornamental aquarium 
trade is unrestricted, and the number collected has steadily declined since the mid-1990?s 
even though fishing regulations were not changed until 2005 (Chapter I). The large 
decrease in B. annulata collected over this time period indicates that members of this 
species are becoming rare on Florida reefs as a result of improper management. Any 
decrease in the host anemone B. annulata wil cause a decrease in the abundance of other 
members of this holobiont, especially the obligate cleaner shrimp associates, so this 
decrease likely has far-reaching cascade effects on these reefs. Shuman et al. (2005) 
concluded that limiting or ending the collection of giant host anemones on coral reefs in 
Indonesian would ?reduce the indirect effects on anemonefish populations?. The same 
principle likely holds for the host anemone B. annulata in the Caribbean, in that placing 
scientifically-based limits on the commercial collection of this species would result in 
positive indirect effects on its crustacean symbionts, client fish who visit these cleaning 
stations, and other reef organisms. In Puerto Rico, limitations have been placed on the 
collection of B. annultata: Thirty-five individuals may be collected per week per 
commercial collector (Hardin and LeGore 2005). Due to a lack of information on the 
demography of this anemone and its abundance on Puerto Rican reefs, it is not known 
whether current restrictions on the number of anemones collected have resulted in 
increase, stability, or decrease in population sizes.  
 Studies have been conducted on the population dynamics of a variety of stony and 
soft corals (Grigg 1977, Hughes and Tanner 2000, Tkachenko et al. 2007) and a few 
species of temperate sea anemones (Ottaway 1979, 1980, Sebens 1983), but litle 
demographic information exists for coral reef sea anemones worldwide. I describe here 
22 
how population dynamics of the corkscrew anemone Bartholomea annulata vary between 
2 reef sites and among 4 seasons over 1 year, and discuss how the 2 types of reefs 
examined may influence population structure in this species. 
 
Methods 
 
Study site characteristics 
The present study was conducted during March 2007-March 2008 at 2 coral reef 
sites on St. Thomas, US Virgin Islands (USVI). The study sites were selected due to 
their proximity to the MacLean Marine Science Center (MSC) of the University of the 
Virgin Islands (UVI), which provided support for diving operations. In addition, 
commercial collecting of sea anemones does not occur in the USVI, thus allowing 
assesment of unfished populations. The two coral reef sites were: (1) Flat Cay, about 
2.2 km offshore, and (2) Brewers Bay, an inshore reef about 200 m from the beach at the 
MSC (Fig. 2.1). Both sites were located at 6-10 m depth below sea surface and 
contained abundant individuals of B. annulata, but difered in their physical 
characteristics. Flat Cay was a typical offshore Caribbean patch reef with a lower rate of 
sedimentation and significantly higher sediment grain size, light penetration, water flow, 
and percent coral cover than on the reef at Brewers Bay (Table 2.1), which was a typical 
inshore patch reef. The Brewers Bay site, which was enclosed partially by an airport 
runway since 1979 (Rogers 1990), periodically received heavy runoff after rainfall on the 
nearby island of St. Thomas, resulting in high sedimentation and low light levels relative 
to Flat Cay. Much of the reef consisted of non-living coral rock, and the few live stony 
23 
corals appeared stressed and partially bleached (N. E. Chadwick, pers. comm.). Despite 
the apparently marginal reef conditions in Brewers Bay, individuals of B. annulata were 
abundant at this site, often attached to small patches of hard substrate surrounded by 
sand, including discarded shoes that had drifted close to the patch reef. The areas 
selected at each site for monitoring of anemone population dynamics were along the 
margin of the reef, where small patches of coral were interspersed with sand (see maps, 
Fig. 2.2A, B). This reef habitat supported maximal abundance of B. annulata. Similar 
habitat along the reef margin also supported the highest abundance of B. annulata sea 
anemones in previous studies in the USVI (Mahnken 1972) 
 Light intensity was measured in ?E m
-2
 s
-1
 every 30 minutes during October 21-
November 29, 2006 by a HOBO Pendant Temperature/Light Data Logger placed 0.5 m 
above the substrate on a rebar stake at about 8m depth at both sites. Light intensities 
were compared between the 2 sites both during peak daylight hours (11:00 AM-1:00 PM) 
and over the entire daylight period (6:30 AM-5:30 PM).  
 Sediment grain sizes were determined by collecting sediment in 50ml centrifuge 
tubes (N=3 at each site) that were pushed into the soft substratum adjacent to the reef at 
each site. Only two of the tubes were analyzed from Flat Cay because one sample was 
damaged prior to analysis. The sediment from each tube was rinsed with freshwater to 
remove salt residues, allowed to dry, and then placed in an 8-sieve with mesh sizes of 
4mm, 2mm, and 850, 425, 250, 180, 150, and 63 microns, and shaken for 5 minutes. The 
mean grain size of sediments was calculated as a weighted average, where the percent of 
the total weight of the sediment on each sieve was multiplied by (mesh of sieve + mesh 
of sieve one size larger)/2.  
24 
 Rates of sedimentation were determined by deploying sediment traps (N=3) at 
each site, each consisting of a PVC pipe (25 x 5 cm) attached at 1m above the soft 
substratum on a rebar stake. Sediment traps were collected 5 days after deployment at 
Flat Cay, and 6 days after deployment at Brewers Bay (after Gilmour 2002). 
 Relative rates of water flow at each site were determined using the clod card 
method (Jokiel and Morrisey 1993). Clod cards were made by placing plaster of Paris 
into 2 ice trays with 16 wells each of 30 ml volume per well, allowing the plaster to dry, 
and weighing each dried clod of plaster. The clods then were glued onto plastic sheets 
using epoxy, and deployed on 5 September 2007 at each site (N=10 clods per site), by 
attaching them to the reef near sea anemones. Only 9 clods were analyzed from Brewers 
Bay because 1 was lost. After 24 hours, the clod cards were retrieved and allowed to dry, 
then reweighed and the percent and absolute change in mass were determined for each 
clod. 
 The percent cover of major benthic organisms at each site was determined from 
photo-quadrats. A 50-m transect tape was deployed along the margin of the patch reef at 
each site at about 8m depth, where individuals of B. annulata are most abundant (see 
above). At Flat Cay, 20 photographs were taken and at Brewers Bay, 24 photos were 
taken, each .05 m
2
 (25x20 cm) at random intervals along the transect tape. A random 
number generator was used to select the points on the 50 m transect. Percent cover was 
estimated for 6 categories of benthos: live stony corals, macroalgae, other live organisms, 
non-living coral skeleton, other hard substrate, and soft substrate. A grid of 25 randomly-
generated points was superimposed over each photograph, and the type of benthos under 
each point was determined (after Walker et al. 2007).  
25 
 
Sea anemone population dynamics 
 All individuals of B. annulata along the reef margin were tagged and mapped at 
each study site. During March 2007, the population of B. annulata at Brewers Bay was 
109 individuals and at Flat Cay 53 individuals, similar to those used by Sebens (1981) 
and Hattori (2006) for determination of demographic patterns in sea anemones. At 
Brewers Bay, the examined population was distributed over an area of 47 x 6 m (282 m
2
) 
along the reef margin. At Flat Cay, an area of 70 x 11 m (790 m
2
) was monitored along 
the reef margin, plus 73 x 5 m (365 m
2
) of sandy area containing small patch reefs 
perpendicular to the reef margin (Fig. 2.2A, B). A much larger area was monitored at 
Flat Cay than at Brewers Bay, because the anemones were much less abundant than at 
Brewers. An aluminum oval tag engraved with a number was attached to a stainless steel 
nail and hammered into the reef substrate adjacent to each anemone. In addition, a short 
piece of flagging tape was tied around each nail to aid in tag relocation. During each 
census, encrusting organisms were removed from the tag, and the flagging was replaced. 
This method of marking large reef anemones appears to be accurate, because most giant 
anemones on coral reefs attach their bases deep within reef holes and crevices, and do not 
appear to locomote across the substratum (Chadwick and Arvedlund 2005). The 
following data were recorded for each tagged sea anemone: species, tentacle crown 
length and width in cm (for calculating the tentacle crown surface area [TCSA], after 
Hirose 1985, Hattori 2002, Chadwick and Arvedlund 2005), orientation (oral disc facing 
up = horizontal or oral facing sideways = vertical), microhabitat (anemone contacting live 
coral, non-living coral rock, and/or sand), depth below sea level, number and species of 
26 
commensal shrimps, state of tentacle expansion, and notes on anything else of interest 
such as anemone color pattern. From the tentacle crown length and width, the tentacle 
crown surface area (TCSA) was calculated using the formula (L/2*W/2)*!), where L = 
tentacle crown length, and W = tentacle crown width. This parameter of body size was 
used because the oral disk and tentacle crown of individuals of B. annulata are slightly 
oblong, as in many other coral reef sea anemones (Hirose 1985, Hattori 2002). The 
location of each sea anemone was recorded on a map for ease of relocation (Fig. 2.2A, 
B). Every 3 months for 1 year (March 07-March 08), the sites were revisited and the 
above data were collected on each marked anemone. The sites also were examined 
carefully for any new recruits of B. annulata during each sample period, which then were 
tagged and censused. Anemones that disappeared between samples were considered to 
have been lost to the population. No anemones were observed locomoting across the site 
or freely floating in the water column. Observations on other giant sea anemones 
indicate that if individuals leave their holes, they likely are preyed upon (N. E. Chadwick 
pers. comm.). Thus, substantial movement of anemones within the study sites appeared 
to be low. From the above demographic data, patterns of recruitment, growth, shrinkage, 
and mortality of the marked anemones within each site were determined. 
 
Data Analysis 
 To quantify patterns of population dynamics in this sea anemone, I used size-
based transition matrices (after Lefkovitch 1967, Hughes 1984). If an individual was 
recorded as absent during only one of the middle censes but present in the next sampling, 
it was considered to be alive but not sampled during that census. Sometimes tagged 
26 
commensal shrimps, state of tentacle expansion, and notes on anything else of interest 
such as anemone color patern. From the tentacle crown length and width, the tentacle 
crown surface area (TCSA) was calculated using the formula (L/2*W/2)*!), where L = 
tentacle crown length, and W = tentacle crown width. This parameter of body size was 
used because the oral disk and tentacle crown of individuals of B. annulata are slightly 
oblong, as in many other coral ref sea anemones (Hirose 1985, Hatori 2002). The 
location of each sea anemone was recorded on a map for ease of relocation (Fig. 2.2A, 
B). Every 3 months for 1 year (March 07-March 08), the sites were revisited and the 
above data were collected on each marked anemone. The sites also were examined 
carefully for any new recruits of B. annulata during each sample period, which then were 
tagged and censused. Anemones that disappeared between samples were considered to 
have been lost to the population. No anemones were observed locomoting across the site 
or frely floating in the water column. Observations on other giant sea anemones 
indicate that if individuals leave their holes, they likely are preyed upon (N. E. Chadwick 
pers. comm.). Thus, substantial movement of anemones within the study sites appeared 
to be low. From the above demographic data, paterns of recruitment, growth, shrinkage, 
and mortality of the marked anemones within each site were determined. 
 
Data Analysis 
 To quantify paterns of population dynamics in this sea anemone, I used size-
based transition matrices (after Lefkovitch 1967, Hughes 1984). If an individual was 
recorded as absent during only one of the middle censes but present in the next sampling, 
it was considered to be alive but not sampled during that census. Sometimes tagged 
28 
aspect of population change (reproduction/recruitment, growth, stasis, shrinkage, and 
mortality) using t-tests, chi-squared tests, and 2-way ANOVAs (SAS v. 9.1). 
 
Results 
 
Study Site Characteristics 
 During midday at 7-8 m depth, levels of iradiance were 3x higher at Flat Cay 
than at Brewers Bay (Table 2.1, 2-tailed t-test, t=14.53, p<0.0001). Iradiance levels also 
were >2x higher at Flat Cay for the entire daylight period (Table 2.1, t=14.96, p<0.0001). 
Sediment particle size also was significantly larger at Flat Cay than at Brewers Bay 
(Table 2.1, t=5.404, p=0.012). The sediment surrounding the reef patch was visibly fine 
and silty at Brewers Bay, while it was much coarser at Flat Cay. There was no 
significant diference in sedimentation rate between Brewers Bay and Flat Key (Table 
2.1, t=0.074, p=0.945). However, this lack of diference likely was due to the very small 
sample sizes of sediment traps (N=3 at Flat Cay and N=3 at Brewers Bay). Both the 
percent and absolute loss of mass of the clod cards per unit time was significantly higher 
at Flat Cay than at Brewers Bay, indicating higher levels of water motion (Table 2.1, 
t=4.07, p<0.001 for percent change, and t=3.28, p<0.01 for absolute change). The 
percent live coral cover also was significantly greater at Flat Cay than at Brewers Bay 
(Table 2.1, t=3.037, p<0.01). Also at Brewers Bay, significantly more of the reef 
substratum was covered by sand that at Flat Cay (22.7?20.6% compared to 9.6?15.4%, at 
Flat Cay, t=2.37, p<0.05), and by macroalgae (20.7?24.3% compared to 6.2?7.8%, 
t=2.54, p<0.05, Fig. 2.6).  Thus, the reef site at Brewers Bay had much lower iradiance, 
29 
sediment grain size, water motion, and coral cover than at Flat Cay, and also more 
macroalgae and sand cover. 
 
Sea Anemone Population Dynamics 
 At the start of the study in March 2007, the abundance of individuals of 
Bartholomea annulata was almost 10-fold greater at Brewers Bay (0.387 per m
2
, or 109 
individuals total per 282 m
2
 area examined) than at Flat Cay (0.046 per m
2
, or 53 
individuals total per 1155 m
2
 area examined). Anemone abundance increased by about 
12% at Brewers Bay and 43% at Flat Cay during the year, and by March 2008 there were 
0.433 individuals per m
2
 at Brewers Bay and 0.067 individuals per m
2
 at Flat Cay. In 
terms of microhabitat use, at both sites, most of the anemones oriented vertically, with 
their oral disks facing sideways, while a minority of individuals faced upwards 
(horizontally, Fig. 2.3A). Most of the anemones occupied holes hear the bases of small 
patch reefs, along the reef-sand interface. A minority of individuals occupied holes 
within the reef framework, with their tentacles surrounded by nonliving reef rock or in 
some cases touching live corals (Fig. 2.3B). 
 The ratio of tentacle crown length:width in individuals of B. annulata was on 
average 2.20:1 at Brewers Bay and 2.10:1 at Flat Cay in March 2007, indicating that 
these anemones possessed oval tentacle crowns that were about 2x as long as they were 
wide. Body shape did not vary significantly between the two sites (t-test, t=0.413, 
p=0.680). At the start of the study, the population size structure of B. annulata difered 
significantly between the two reef sites (Chi-squared test, !
2
=31.14, p<0.001, Fig. 2.4) 
and remained significantly diferent throughout the study period (June 07 !
2
=38.25, Sept. 
30 
07 !
2
=31.15, Dec. 07 !
2
=51.22, Mar. 08 !
2
=48.32, p<0.001 for all). At Brewers Bay, 
individuals ranged in size from 0.79 to 451.60 cm
2
 TCSA (tentacle crown surface area, 1 
x 0.5 cm and 25 x 23 cm respectively), while at Flat Cay they ranged from 1.57 to only 
98.90 cm
2 
(1 x 1 cm and 25 x 5 cm respectively). At Brewers Bay, about half the 
anemones occupied the smallest size-class of 0-25 cm
2
 TCSA, while at Flat Cay almost 
70% were in the smallest size class, and none of the individuals were in the largest size-
class of >100 cm
2
. Throughout the entire study period none of the anemones at Flat Cay 
grew into the >100 cm
2
 size-class. Thus, individuals were significantly smaller at Flat 
Cay than at Brewers Bay (2-tailed t-test, t=2.879, p<0.01) and remained so throughout 
the year (Mar. 08, t=4.073, p<0.0001).  
 In terms of changes in body size, during all seasons examined, a higher percent of 
individuals in the population grew to another size-class at Brewers Bay than at Flat Cay, 
ranging from 13% - 30% at Brewers Bay and 3% - 29% at Flat Cay (Table 2.2). This 
diference in growth between the sites was significant during the summer and fall only 
(!
2
=19.51, p<0.001 for summer, and !
2
=12.66, p<0.001 for Fall, but !
2
=0.03, p>0.5 for 
Spring and !
2
=3.66, p>0.05 for Winter). On average among seasons, at Brewers Bay a 
higher percent of individuals grew from one size-class to another for all size-classes 
while at Flat Cay, no anemones grew into either of the largest 2 size-classes (Table 2.3). 
This diference between sites in the mean growth rate of each size class was significant 
only for the 50.1-75 cm
2
 size class (2-tailed t-test, t=12.48, p<0.0001). During half the 
seasons, a significantly larger percent of individuals also transitioned to a smaller size-
class (shrank) at Brewers Bay than at Flat Cay, indicating a more dynamic population at 
the former site (Table 2.2, !
2
=9.70, p<0.01 for Sumer, !
2
=5.64, p<0.05 for Fall, but 
31 
!
2
=4.67, p=0.05 for Winter, and !
2
=1.22, >0.1 for Spring). In contrast, average 
shrinkage rates were higher at Flat Cay than Brewers Bay for 3 of 4 size-classes (Table 
2.3). On average, 90% of anemones shrank from the 75.1-100 cm
2
 at Flat Cay, but the 
diferences were not significant. This apparently paradoxical trend resulted from the lack 
of large individuals at Flat Cay. Since there were no individuals of the largest size class 
at Flat Cay, they could not shrink, whereas, about 40% of the largest individuals shrank at 
Brewers Bay. The high shrinkage rate of large individuals at Brewers Bay increased the 
percentage of anemones that shrank during each season. Rates of retention of animals in 
the same size-class (stasis) also were higher at Brewers Bay than at Flat Cay during most 
seasons (Table 2.2), but this diference was significant only during Summer (!
2
=9.05, 
p<0.01 for Summer, but !
2
=2.38, p>0.1 for Spring, !
2
=1.24, p>0.1 for Fall, and !
2
=3.70, 
p>0.05 for Winter). The percent of individuals that remained in the same size class was 
similar during all seasons at Brewers Bay, but the number decreased dramatically during 
the Summer at Flat Cay relative to the other seasons. Average retention rates within each 
size class for all the seasons also were higher at Brewers Bay than at Flat Cay, in 4 of the 
5 size-classes (Table 2.3) but the diferences were not significant. A 2-way ANOVA of 
percent change in body size with site and size-class revealed no significant effects during 
any season except for the Fall, when anemone size change was significantly greater at 
Brewers Bay than at Flat Key. Thus, the population at Brewers Bay was more dynamic 
than the one at Flat Cay, in terms of the percent of individuals that transitioned among 
size-classes through growth, shrinkage, and the retention of live individuals, but there 
was no significant effect on the size change of individual anemones within the size 
classes. 
32 
 Rates of mortality (loss of individuals from the population) at Flat Cay were 
significantly higher than those at Brewers Bay during Spring and Summer, but not during 
Fall and Winter (Chi
2
, Spring !
2
=5.24, p<0.05, Sumer !
2
=51.32, p<0.001, Fall 
!
2
=0.882, p>0.1, and Winter !
2
=0.165, p>0.5, Table 2.2). Peak mortality occurred 
during Summer at Flat Cay, when 64% of anemones died, which was >20% higher than 
mortality rates in other seasons. Rates of mortality were higher at Brewers Bay than Flat 
Cay for the largest size-classes, but were lower for the smallest individuals (Table 2.3). 
Diferences in mortality between the 2 sites were significant only for the smallest size 
class (2-tailed t-test, t=2.45, p<0.05). 
 Recruitment rates of new individuals into the population (Table 2.4) were 
significantly more rapid at Brewers Bay than at Flat Cay, both in terms of recruitment per 
unit area (2-tailed t-test, t=7.13, p<0.001) and per resident per unit area on the reef 
(t=3.64, p<0.05). However, there was no significant diference in total recruitment per 
site (t=1.033, p=0.341), because a much smaller area was examined at Brewers Bay (see 
above). The opposite pattern emerged in terms of recruitment rate per resident anemone 
(Table 2.4), in that more recruits appeared relative to the low total number of anemones 
at Flat Cay, than per to the large number at Brewers Bay. However, this diference 
between sites in the number of recruits per resident was not significant (t=1.594, 
p=0.162).  
 Dynamic survival curves calculated from the observed loss of individuals during 
the study revealed that anemones survived longer at Brewers Bay than at Flat Cay (Fig. 
2.5A). Static survival curves constructed from the population size-structure at each site 
also revealed the same trend (Fig. 2.5B).  
33 
 
Discusion 
 I show here that populations of the corkscrew anemone Bartholomea annulata are 
extremely dynamic, with high rates of mortality and recruitment during a single year, as 
well as large proportions of anemones transitioning among size-classes via growth and 
shrinkage. The highly dynamic nature of these populations has important implications 
for the mobility and dynamics of the obligate anemoneshrimps, including the shrimp 
cleaners of reef fish parasites (Nizinski 1989, Crawford 1992, Gwaltney and Brooks 
1994). 
 Rates of stasis in B. annulata (10-50% of individuals remaining in the same size 
class per 3 months) were an order of magnitude lower than those known for some 
Caribbean reef-building corals: 10-60% of individuals of the massive coral Porites 
astreoides remained in the same size classes for 3 years, and up to 74% of Montastrea 
annularis, 50% of Agaricia agaricites, and 71% of Leptoseris cucullata individuals 
remained in the same size classes for 5 years (Hughes and Tanner 2000, Lirman and 
Miler 2003). Thus, stasis rates over a 3-month period for the sea anemones were similar 
to stasis over 3-5 years in the coral populations. Another key diference was that in these 
corals, larger individuals were more likely to remain in the same size-class than were 
smaller individuals, whereas in the sea anemone they were not. On Australian coral 
reefs, Babcock (1991) showed that two-year stasis rates for 3 species of brain coral 
ranged from 27%-90%, with a mean of 46.25% remaining in the same size-class for 
Platygyra sinensis, 56.6% for Goniastrea aspera, and 55.5% for G. favulus.  Thus, stasis 
rates for Indo-Pacific corals also were much higher than those for this coral reef sea 
34 
anemone, indicating less turnover in coral populations than for the sea anemones. 
 In addition to low stasis, the sea anemone populations experienced rates of 
mortality that were an order of magnitude higher than those known for stony corals on 
reefs. Mortality for B. annulata was 10-54% per 3 months, compared to 52-100% for 
Leptoseris cucullata, 0-89% for Montastrea annularis, and 27-89% for Agarcia 
agaricites per 5 years (Hughes and Tanner 2000), and 9-20% per 3 years for the massive 
Caribbean coral Porites astroides (Lirman and Miler 2003). Thus, the corals had 
turnover rates of individuals on the order of years, while the anemone individuals were 
replaced on a scale of months. Mortality rates in the above coral species decrease with 
colony size, but in B. annulata they were highly variable among seasons and did not vary 
significantly among size-classes. The decrease in mortality with colony size in the above 
coral species indicates an advantage of coloniality: when a large coral colony is damaged, 
most of the polyps within the colony may survive, but if a large sea anemone is damaged, 
the end result may be death of the entire solitary polyp. This pattern may cause mortality 
to decrease with size in colonial corals but not in solitary sea anemones such as B. 
annulata.  
 Rates of growth and shrinkage of individuals varied significantly among size 
classes in B. annulata, in that growth rates decreased and shrinkage rates increased as the 
anemones became larger. This pattern was similar to that observed in all other stony 
corals (Hughes 1984, Hughes and Jackson 1985, Hughes and Tanner 2000) and temperate 
sea anemones (Ottaway 1980) examined to date. In corals that rarely shrink and thus can 
be aged accurately, rates of growth also decrease with the age and size of individuals 
(Chadwick-Furman et al. 2000, Gofredo et al. 2004, Guzner et al. 2007). In all cases, 
35 
reef cnidarians appear to grow rapidly when small and young, and to decrease their 
growth rates with age. In species with partial mortality or tisue shrinkage, such as many 
corals and sea anemones, shrinkage also appears to be more common in the largest 
individuals. 
 Rates of growth in terms of both absolute surface area (up to 338 cm
2
 per 3 
months) and percent of total body size (an astounding 5,070% per 3 months) in B. 
annulata were much more rapid than they are for massive stony corals, which are known 
to grow up to 2 cm in radial growth per year (~12.6 cm
2
, Hughes and Jackson 1985). 
 They also are more rapid than rates recorded for temperate sea anemones, which in New 
Zealand grow only 0.6 cm in basal diameter per year (Ottaway 1980), and in the 
Mediterranean Sea up to 20% of basal diameter in 3 months (Chomsky et al. 2004a). 
 Individuals of B. annulata may grow more rapidly than do tropical scleractininian corals 
because they do not need to invest energy and materials into construction of a hard 
skeleton as they grow. In addition, they may grow more rapidly than do temperate sea 
anemones, because they experience higher temperatures and light levels in the tropics, 
both of which correlate with more rapid growth in photosynthetic cnidarians (Chomsky et 
al. 2004b).  
 I quantify here for the first time demographic patterns in a tropical sea anemone. 
The population dynamics of other large coral reef anemones are expected to be more 
similar to those of this sea anemone than to stony corals on reefs, in that they may be 
quite dynamic relative to corals. 
 The significant diferences in population size structure and dynamics between the 
two sites examined suggest that characteristics of the offshore site at Flat Cay restrict 
36 
anemone growth rates, augment shrinkage, and reduce individual survival. Individuals of 
this sea anemone posses extremely long, thin tentacles and a long narrow column that 
are easily distorted by water motion (M. Nelsen and N. Chadwick pers. obs.). In the 
laboratory aquaria, individuals of this species avoid areas of high water flow, and attach 
their bases in areas with lower flow, where they are able to fuly extend their long 
delicate tentacles (M. Nelsen pers. obs.). Drag, caused by the force of movement across a 
surface, is known to have a large influence on benthic organisms, and as body size or 
flow speed increases so does the amount of drag on the deformable bodies of sea 
anemones (Koehl 1977, 1984). Thus, the significantly higher water motion at Flat Cay 
than at Brewers Bay may prevent these anemones from fully extending their delicate 
tentacles to feed, and also to expose their zooxanthellae to light, and consequently may 
limit them to smaller sizes as a result of increased in mechanical stress. It is also possible 
that greater water motion increases energetic demands needed to maintain inflated size 
and for repair of tisue damage resulting from water motion. The anemones may 
experience equal drag overall at both locations, because the slower flow speed at Brewers 
Bay allows body size to become larger than at Flat Cay. During seasonal storms when 
water motion is especially high, many of the individuals at Flat Cay withdraw completely 
under rocks at the reef-sand interface, and then re-emerge a few days later after the storm 
has passed (S. Ratchford and N. E. Chadwick unpubl. data). In contrast, individuals at 
Brewers Bay remain expanded during seasonal storms, possibly due to the much lower 
levels of water motion that are generated at this protected inshore site. 
 The 20% higher growth rate of anemones at Brewers Bay than at Flat Cay in the 
summer when iradiance is highest and possibly zooplanktonic food supplies are as well, 
37 
implies that seasonal characteristics of the latter site also restrict maximum anemone size. 
The higher shrinkage rates at Brewers Bay appear to result from the greater individual 
growth rate at this site, and thus the greater amount of larger individuals that are capable 
of shrinking substantially. The pattern of nearly 70% of anemones at Flat Cay occupying 
the smallest size class versus only 50% at Brewers Bay is explained in part by the much 
slower growth rates and higher mortality of small individuals at the former site. In 
addition, the high rates of stasis as well as growth at Brewers Bay relative to Flat Cay 
combined with higher survival, explain why there are relatively more individuals overall, 
and especially more in the largest size classes, than at the latter site. Disparities in 
mortality and growth are especially large during sumer, when 64% of the anemones at 
Flat Cay die versus only 18% at Brewers Bay. The summer to fall period in the 
Caribbean is the season of tropical storms and hurricanes, which may greatly increase 
water motion at the exposed outer site of Flat Cay. Thus, I conclude that large 
diferences in mortality and growth between the two examined sites during summer may 
be due in part to storm-generated water motion.   
 The survival curves indicated that only 5% of individuals remain alive after 26 
months at Brewers Bay, thus the original population turns over almost completely within 
about 2 years. In contrast, only 5% of the population remains after a much shorter time 
of 13 months at Flat Cay, indicating a turnover time of about 1 year. Thus, if both 
populations were to suffer from recruitment failure, the population at Flat Cay would 
decrease to zero twice as fast as that at Brewers Bay, due to slow anemone growth and 
high mortality at the former site. Along with that, a comparison of the two survival 
38 
curves indicates that not only are individuals more likely to survive longer at Brewers 
Bay, but they also are more likely to grow larger during the same time period as well. 
 Although total recruitment was similar at the two sites, the number of recruits 
both per m
2
 and per resident per m
2
 was much greater at Brewers Bay than at Flat Cay. 
The number of recruits per resident per m
2
 was twice as high at Brewers Bay as at Flat 
Cay, indicating that a high abundance of large adult anemones may enhance local 
recruitment. This pattern occurs in many cnidarians, including reef-building corals, and 
indicates that self-recruitment may be common in populations of coral reef cnidarians, in 
that recruitment is determined largely by local population density (Hughes et al. 2000, 
Glassom et al. 2004). In addition, because these anemones reproduce asexually as well 
as sexually (Jennison 1981), the number of local residents may even more strongly 
influence local recruitment patterns. Sexual versus asexual recruits were not 
distinguished in the present study, in part because special methods need to be developed 
to separate these 2 types of recruits. The relative importance of these two reproductive 
modes to population growth is an important avenue for future research. Despite the low 
number of new recruits per resident per m
2
 at Flat Cay, there was no significant 
diference in total recruits between sites. Thus, despite the overall lower population 
density at Flat Cay than at Brewers Bay, many recruits arrived, implying that new recruits 
may be coming from an outside population. Therefore, diferent factors may be driving 
each population. The Brewers Bay population may be driven largely by self-recruitment 
of sexual propagules and/or asexual reproduction, while the Flat Cay population may be 
driven largely by recruitment from an external source population. 
39 
 The lack of a hard skeleton and the potential mobility of sea anemones caused 
some problems to arise while conducting this study. In the surveys, there were 4 possible 
outcomes for each tagged anemone: present with tag, present but tag lost, absent but tag 
stil there, or both the tag and anemone gone. If the anemone and the tag were present, 
data were collected. If the tag was absent, either the anemone had died or had moved, 
and no conclusions could be drawn. In the case of anemone absence, the lack of a 
skeleton made it impossible to tell whether that individual at moved or died. In this 
study, all mising anemones were assumed deceased, because exposed anemones likely 
were preyed upon. For tags that were mising, anemones were considered dead if the 
tags were not found during two consecutive censes (had not been found in 6 months). 
 I conclude that demographic patterns in the corkscrew anemone Bartholomea 
annulata reveal highly dynamic populations that vary widely between in shore and of 
shore sites, and thus may be influenced strongly by reef characteristics. Diferences is 
water flow, percent coral cover, iradiance, and/or particle size between the sites may 
explain why the anemone population at Brewers Bay was larger, had higher survivorship, 
and contained individuals with larger body sizes than did the population at Flat Cay. In 
addition, the local abundance of individuals appeared to largely influence recruitment 
rates, indicating that whether sexual or asexual, recruitment may be mainly local. These 
patterns have major implications for the stability and abundance of obligate 
anemoneshrimps that rely on this host anemone for essential habitat. Given the evidence 
on dynamics of B. annulata populations presented here, one would also expect that 
populations of their symbiotic anemoneshrimp would also be highly mobile and dynamic 
in order to track the rapidly changing host populations. By inference, so must the 
40 
behavior of fishes that rely on anemone-associated cleaner shrimps for daily removal of 
ectoparasites (Sikkel et al. 2004). An additional implication of this study is that site-
specific population data are needed to create a scientific basis for sustainable fisheries on 
this host anemone and associated anemoneshrimps.
41 
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48 
Table 2.1. Statistical results of 2-tailed t-tests on diferences in physical characteristics 
between 2 coral reef sites (Brewers Bay and Flat Cay). Sediment size, iradiance at peak 
hours, iradiance during the entire daylight period, percent change in clod card mass, 
absolute change in clod card mass, and percent stony coral cover all were significantly 
greater at Flat Cay than at Brewers Bay, while there was no significant diference in 
sedimentation rate between the 2 sites. 
 
 Sediment 
Size 
(?SD) 
Irradiance 
Peak Hours 
(?SEM) 
Irradiance 
Entire 
Daylight 
Period 
(?SEM) 
% Change in 
Clod Card 
Mas 
(?SD) 
Absolute 
Change in 
Clod Card 
Mas 
(?SD) 
Percent 
Stony 
Coral Cover 
(?SD) 
Sedimentation 
Rate 
(?SD) 
Brewers 
Bay 
0.53?.04 
mm 
N=3 
59.2?3.3 
?E m
-2
 s
-1 
N=40 
37.8?.04 ?E 
m
-2
 s
-1 
N=40 
19.1?.91% 
N=9 
8.2?.37 g 
N=9 
15.2?15.3
% 
N=20 
0.06?.02 g d
-1 
N=3 
Flat 
Cay 
0.75?.04 
mm 
N=2 
194.6?8.8 
?E m
-2
 s
-1 
N=40 
10.9?3.8 
?E m
-2
 s
-1 
N-40 
20.8?1.1% 
N=10 
8.9?.53 g 
N=10 
31.0?19.3
% 
N=24 
0.06?.06 g d
-1 
N=3 
t-value 5.404 14.53 14.96 4.07 3.28 3.037 0.074 
P-value <.05 <.001 <.001 <.01 <.01 <.01 .945 
 
49 
Table 2.2 Variation among seasons and sites in the percent of anemones that either 
grew, shrank, remained in the same size class, or died (based on TCSA).  
 
Brewers Bay Spring Sumer Fal Winter 
Growth 19.6% 30.5% 12.9% 16.9% 
Shrinkage 13.1% 14.3% 15.6% 14.0% 
Stasis 39.3% 37.1% 37.4% 29.4% 
Mortality 28.0% 18.1% 34.0% 39.7% 
     
Flat Cay Spring Sumer Fal Winter 
Growth 18.9% 10.5% 2.9% 9.9% 
Shrinkage 9.4% 4.7% 26.5% 7.0% 
Stasis 30.2% 20.9% 30.9% 40.8% 
Mortality 41.5% 64.0% 39.7% 42.3% 
 
Table 2.3. Variation among size classes and sites in the mean percent of individuals (? 
S.D.) that either grew, shrank, remained in the same size class, or died (based on TCSA, 
N=4 seasons, NA= not applicable). 
   
Brewers Bay 0-25 cm
2 
25.1-50 cm
2 
50.1-75 cm
2 
75.1-10 cm
2 
>10 cm
2 
Growth 20.2?1.6% 26.3?8.0% 23.0?3.7% 19.2?18.7% NA 
Shrinkage NA 18.0?6.2% 37.0?19.2% 31.8?25.9% 39.7?6.2% 
Stasis 50.1?6.2% 21.1?7.4% 17.1?7.9% 17.5?15.5% 37.0?10.2% 
Mortality 29.7?17.2% 34.6?6.3% 2.9?16.7% 31.5?21.2% 23.3?8.5% 
      
Flat Cay 0-25 cm
2 
25.1-50 cm
2 
50.1-75 cm
2 
75.1-10 cm
2 
>10 cm
2 
Growth 10.0?6.2% 17.0?13.4% 0.0% 0.0% NA 
Shrinkage NA 27.0?1.9% 49.2?20.6% 90.0+/14.1% NA 
Stasis 35.9?10.5% 27.9?1.6% 10.0?1.5% 0.0% NA 
Mortality 54.1?10.7% 28.1?13.9% 40.8?17.7% 10.0?14.1% NA 
 
50 
Table 2.4. Variation in rates of recruitment of new anemones between 2 coral reef sites.  
Data are presented as mean percent of individuals ? 1 standard deviation. N=4 seasons 
examined. 
 
 Total Recruitment Recruits/m
2 
Recruits/Resident Recruits/Resident/m
2 
Brewers Bay 47?9.05 .17?.03 0.42?.12 .015?.004 
Flat Cay 39.8?10.70 .04?.01 .67?.30 .006?.003 
51 
Figure Legends 
Fig. 2.1. Maps showing 2 coral reef sites examined for sea anemone population 
dynamics near the island of St. Thomas, USVI. Site #1 Brewers Bay, is 200 m from 
island, and site #2 Flat Cay is 2.2 km from island. 
Fig. 2.2. Maps from Dec. 2007 showing locations of tagged sea anemones along the reef-
sand margin at: A. the Brewers Bay study site. B. the Flat Cay study site. Numbers refer 
to the tag number of each anemone. 
Fig. 2.3A. Percent of anemones oriented horizontally, vertically, and midway between 
horizontally/vertically at Brewers Bay and Flat Cay. At both locations, most of 
anemones were oriented vertically. Data are presented as means ? 95% CI, N=104 
anemones examined at Brewers Bay and N=52 anemones examined at Flat Cay.  B. 
Percent of anemones that were located in each microhabitat. Most anemones were found 
at the rock/sand interface at both locations. Data are presented as means ? 95% CI, 
N=102 anemones examined at Brewers Bay and N=52 anemones examined at Flat Cay. 
Fig. 2.4. Population size-structure of the sea anemone Bartholomea annulata at 2 coral 
reef sites (Brewers Bay N=108 and Flat Cay N=53). Sea anemones were significantly 
larger, and populations size was significantly greater at Brewers Bay than at Flat Cay (see 
text for details). 
Fig. 2.5A. Dynamic survival curves for Brewers Bay and Flat Cay, from observed 
disappearance of tagged sea anemones at each site over one year of study. Curves show 
that anemones are most likely to survive for one year at Brewers Bay (Brewers Bay, 
y=1.007e
-.17x
 R
2
=.999, Flat Cay, y=1.027e
-.183x
 R
2
=.996). B. Static survival curves for 
Brewers Bay and Flat Cay, constructed from the observed population structure of sea 
52 
anemones at each site during March 2007. Static survival curves show that anemones are 
more likely to grow larger at Brewers Bay than at Flat Cay.
53 
 
 
 
 
Fig. 2.1.
54 
 
 
 
Fig. 2.2A.
55 
 
 
 
 
Fig. 2.2B. 
56 
 
 
 
Fig 2.3.
57 
 
 
Fig. 2.4.
58 
 
 
Fig. 2.5. 
 
59 
CHAPTER II 
 
STAGE-BASED MODELING OF POPULATINO DYNAMICS IN THE 
CORKSCREW ANEMONE BARHTOLOMEA NNULATA 
Introduction 
 Population dynamic modeling has been used to ases the changes in population 
size and structure for several species of stony corals (Grigg 1984, Hughes 1984, Fong and 
Glynn 2000, Hughes and Tanner 2000, and Lirman and Miler 2003), but has not yet been 
applied to actinian sea anemones. Grigg (1984) was the first to apply a standard fisheries 
model to stony corals. However, this type of age-based model applies only to corals that 
rarely fuse, fision, or shrink and thus have a strong relationship between coral size and 
age. Age-based models have been applied to solitary corals (Chadwick-Furman et al. 
2000, Goffredo 2004), and corals that form compact colonies with litle shrinkage 
(Guzner et al. 2007). Hughes (1984) was the first to use a stage-based model for 
organisms such as most stony corals that can suffer from partial mortality, and thus may 
shrink as wel as grow. His model was a variation on the Lefkovitch model (1965) that 
was used initialy to group beetles into life-stage clases based on their stage of 
development (egg, larva, pupae, etc.). These modifications of the original, age-based, 
Leslie model (1945) laid the groundwork for population modeling of organisms that 
cannot be clasified by age.
 
60 
 
 The application of size-based models to sea anemones requires several 
modifications from those used for stony corals. For example, the corkscrew anemone 
Bartholomea annulata (Cnidaria: Anthozoa) forms clones of unconnected individuals via 
pedal laceration (Jennison 1981), and as a result do not produce colonies of connected 
units like the stony corals that have been modeled (see above). Thus, the elements of a 
transition matrix for this sea anemone do not represent change in the size of a colony, but 
rather change in the size of individual polyps. Anemones suffer from partial tisue 
mortality as do corals, but because they have no hard skeleton, their tisue loss is visible 
only as a general shrinkage of the body. Reproduction also must be integrated into the 
model diferently than for stony corals, which can fragment to produce new asexual 
recruits. These asexual recruits often are clearly distinguishable from newly-settled 
sexual recruits due to diferences in their skeletal shape, and thus can be incorporated into 
the model separately. In contrast, newly-budded sea anemones often are 
indistinguishable from new sexual recruits, due to their essentially identical appearance 
(M. Nelsen, personal observation). The ability to distinguish sexually versus asexually 
produced recruits allows for the clear integration of asexual recruits into the coral 
transition matrices. Because this is not possible with sea anemone recruits, it is necesary 
to construct 3 separate models, each with a diferent possible type of reproduction: (1) 
fully-closed recruitment, that assumes all recruits, either sexually or asexually produced, 
arise from within the population, (2) open recruitment, where all recruits arive sexually 
from outside the population, and (3) semi-open recruitment, where relatively large 
individuals are considered to be asexual recruits that arise from within the population, 
 
61 
and small individuals are assumed to be sexual recruits that arise from outside the 
population. 
Bartholomea annulata is one of the largest and most common sea anemones on 
coral reefs in the Caribbean Sea, and yet the litle information that exists on the biology 
of this species, is contained mainly in coral reef guide-books (Colin 1978, Kaplan 1982, 
Sefton & Webster 1986). This lack of information precludes a scientific basis for 
management of commercial fishing of these animals. Individuals of B. annulata are a 
major component of the ornamental aquarium trade (Chapter I), and modeling of their 
demographics wil support the development of a sustainable fishery on this important reef 
species.  Here I use a size-based demographic model to project population trends under 
various recruitment r?gimes for two unfished populations at St. Thomas, US Virgin 
Islands. Modeling of these populations reveals how unfished populations at two reef sites 
maintain demographic stability under various recruitment scenarios, and also highlights 
which life history stages are the most important for maintaining these populations 
(Cropper and DiResta 1999, Caswell 2001, Lirman and Miler 2003). I present here 
information on population growth rates, stable size distributions, and time to convergence 
to stable size structure for each of these two populations, and reveal how they may be 
influenced by local environmental conditions. Finally, I demonstrate how elasticity 
analysis can be used as a management tool for these sea anemones to set restrictions on 
fishing rates, by revealing which life history proceses/vital rates (growth, shrinkage, 
stasis, or recruitment, also known as vital rates) most influence the pace of population 
growth. 
 
 
62 
Methods 
Collection of Population Data 
Field data on population parameters were collected during March 2007-March 
2008 for individuals of the corkscrew anemone Bartholomea annulata at St. Thomas, US 
Virgin Islands (USVI). Two coral reef sites on St. Thomas were examined: (1) an 
offshore patch reef at Flat Cay, and (2) an inshore reef at Brewers Bay. Each 3 months 
during the study year, all individuals of this species were censused within mapped areas 
at both reef sites, and information was collected on the number of new recruits, changes 
in size of resident anemones, and disappearance of individuals from the populations. For 
details on physical characteristics of the field sites, and methods of field data collection, 
see Chapter I. 
 
Population Modeling 
 A size-based population model was created for B. annulata from the above field 
measurements, modified after Hughes (1984, Eq. 3.1), where A (Table 3.1A) is the s x s 
transition matrix, b
t
 is the s x 1 population vector at time t, and b
t+1
 is the s x 1 population 
vector 1 time period later. 
b
t+1
=A*b
t
 (Eq. 3.1) 
A model for each of the two reef sites was created from a size-based life cycle graph for 
B. annulata (Chapter I) in which the anemone life cycle was divided into 5 size-classes of 
tentacle crown surface area (TCSA, 0.1-25 cm
2
, 25.1-50 cm
2
, 50.1-75 cm
2
, 75.1-100 cm
2
, 
and >100 cm
2
), that encompass the range of body sizes of the anemones at these study 
sites (Chapter I). Only individuals in the smallest size-class (0.1-25 cm
2
) were classified 
 
63 
as juveniles that do not reproduce; this is an arbitrary assignment based on the average 
size of anemones without gonads of 7.4 m basal diameter (Jennison 1981).  Transition 
matrices were created, in which the elements contained within were the proportions of 
anemones that transitioned from one size-class to another during each 3-month time step 
(Hughes and Tanner 2000). There were three possible transitions: an anemone grew from 
its size-class to a larger size-class (G), it remained in the same size-class (L), or it shrank 
and transitioned from its curent size-class to a smaller size-class (S). Four seasonal 
matrices were created from the five sampling periods (Spring=A, Summer=B, Fall=C, 
and Winter=D), and from these a one-year transition matrix was created by multiplying 
the four seasonal matrices together (E=D*C*B*A, Caswell 2001). The one-year 
transition matrix (E) projects future populations from the beginning of one spring until 
the beginning of the next (March to March). 
 
Modeling of Reproduction 
 Three models were created to incorporate three diferent possible modes of 
reproduction, and thus of recruitment, into these populations: completely closed, 
completely open, and semi-open. In a completely closed population, all new individuals 
arise from sexual or asexual reproduction by resident anemones within the population. In 
a completely open population, all new individuals are considered to originate through the 
arrival of sexual recruits from outside the population. Finally, in a semi-open population, 
small individuals are sexual recruits that come from outside the population while new 
large individuals are asexual recruits that come from within the population. 
 
64 
 Treating the populations as completely closed assumes that 100% of recruitment 
is local, and therefore that all new individuals are either sexually or asexually produced 
from individuals currently in the population. Fecundity is known to increase with body 
size in marine invertebrates (Cropper and DiResta 1999). Here, anemones with large 
TCSA are expected to have high fecundity and more reproductive output relative to those 
with small TCSA (Eq. 3.2 and 3.3): 
 
N(t+1)=F
1
*n
1
(t)+F
2
*n
2
(t)+F
3
*n
3
(t)+F
4
*n
4
(t)+F
5
*n
5
(t) (Eq. 3.2) 
 
In Eq. 3.2, N is the number of new individuals at time t+1, n
i
 is the number of individuals 
at time t, and F
i
 is the reproductive rate. The subscripts represent the size-classes: 
T=total, 1=0.1-25 cm
2
, 2=25.1-50 cm
2
, 3=50.1-75 cm
2
, 4=75.1-100 cm
2
, and 5=>100 
cm
2
. This equation alone does not reveal the reproductive rate of each size-class, because 
each F
i
 is unknown. Therefore, we can produce five equations based on the assumptions 
that fecundity is proportional to body size, and that the smallest size-class does not 
reproduce. The following equations were used: 
 
F
5
=2.5*F
2 
(Eq. 3.3A) 
F
4
=2*F
2
 (Eq. 3.3B) 
F
3
=1.5*F
2
 (Eq. 3.3C) 
F
2
=1*F
2
 (Eq. 3.3D) 
F
1
=0 (Eq. 3.3E) 
 
 
65 
The constant multipliers in Eq. 3.3A-E represent linear stepwise increases in reproductive 
output (fecundity) based on increases in body size in each size-class. Thus, I may 
underestimate here the reproductive output of very large anemones, because egg number 
in sea anemones increase in a linear fashion with body mass rather than with TCSA, 
which is a 2-dimensional rather than a 3-dimensional measure of body size (Chadwick-
Furman and Spiegel 2000). Equations 3.2 and 3.3 were used to solve for F
i
.  To complete 
the transition matrix, the reproductive rates (F
i
) were added to the transition probabilities. 
N
 
was set equal to the number of new individuals in the smallest size-class the F
1
-F
5
 
values were added to the first row of the transition matrix. This was repeated for each 
size-class (Table 3.1B). 
 Treating the population as being completely open requires a separate recruitment 
vector, r, to be added to Eq. 3.1: 
 
c
t+1
=A*b
t
 + r
t
 (Eq. 3.4) 
 
Observed rates of annual recruitment in the field were used for r
it
, in which r
1t
= # 
recruits/m
2
 of 0.1-25 cm
2
 TCSA, r
2t
= # recruits/m
2
 of 25.1-50 cm
2
, r
3t
= # recruits/m
2
 of 
50.1-75 cm
2
, r
4t
= # recruits/m
2
 of 75.1-100 cm
2
, and r
5t
= # recruits/m
2
 of >100 cm
2
. No 
published information exists on the extent to which new recruits of this sea anemone 
species are sexually versus asexually produced, originate locally or externally to the 
populations, or whether recruitment varies with physical characteristics of the reef 
environment. As such, in addition to the above-observed rates, simulated rates of 
recruitment were used, in which recruitment was classified as either maximal (r
max
, 
 
66 
observed recruitment was the greatest possible recruitment), or average (r
average
, observed 
recruitment was treated as half of the potential recruitment). In each time step, r
t
 was 
determined by sampling randomly from a uniform distribution of 0 to r
max
 recruits/m
2
 for 
maximal recruitment, and 0 to 2*r
max
 for average recruitment (after Fong and Glynn 
1998, Lirman and Miler 2003). This process was repeated 30 times for each of 30 
annual time steps, to project a range of possible future recruitment rates to each 
population. 
 For modeling of the semi-open populations, all large recruits are considered to be 
asexual, and were integrated into the transition matrix (in a similar manner as in the 
closed population) while all small recruits are considered sexual and assumed to come 
from outside of the population. Therefore, eq. 3.4 stil applies for this model, but the 
matrix A is constructed diferently. All new individuals < 50 cm
2
 TCSA were considered 
to be sexual recruits, and new individuals > 50 cm
2
 were considered to be asexually 
recruited clonemates of existing anemones from within the population. To model this 
process, eq. 3.2 was used for the three largest size-classes, and eq. 3.3 was modified such 
that (Eq. 3.5): 
F
5
=5/3*F
3 
(Eq. 3.5A) 
F
4
=4/3*F
3
 (Eq. 3.5B) 
F
3
=1*F
3
 (Eq. 3.5C) 
F
2
=0 (Eq. 3.5D) 
F
1
=0 (Eq. 3.5E) 
The values used in eq. 3.5 are the same as those used in eq. 3.3, except that they have 
been reduced so that the constant in eq. 3.5C is equal to 1. Budding rates are not 
 
67 
currently known for B. annulata, and because of this the same rates are used here as for 
sexual reproduction. The budding rates then were integrated into the transition matrix in 
a similar manner to that used in the closed population. Asexual recruits were classified as 
all new individuals that were >50 cm
2
 in body size, and were assumed to have arisen 
from large anemones >50 cm
2
 in body size. Therefore the recruitment rates were added 
to the 3x3 bottom right corner of the matrix (Table 3.1C). Limits were set on the body 
size of new sexual recruits, because it was unlikely that large recruits were newly-
metamorphosed from planktonic planula larvae, which are known to be 0.5-13.3 m in 
column diameter for the intertidal sea anemone Actinia tenebrosa (Ottaway 1979). In 
addition, laboratory observations indicated that buds of B. annulata may become large 
(up to 180 cm
2
 TCSA) while stil attached to parental polyps, thus large newly-recruited 
anemones likely were pedal lacerated clonemates of resident anemones (M. Nelsen, 
personal observation). In all, 7 possible recruitment scenarios were examined: closed, 
open with observed rates, open with average rates, and open with maximal rates, semi-
open with observed rates, semi-open with average rates, and semi-open with maximal 
rates. Closed population models did not require more than one model, because all 
recruits were considered to be local and therefore the changes made to outside 
recruitment did not apply. Thus, I generated seven thirty-year projections to estimate 
changes in population size and structure for these sea anemones at each of the two study 
sites (after Fong and Glynn 1998, Lirman and Miler 2003). 
 
 
 
 
68 
Data Analyses 
 For each transition matrix, the dominant eigenvalue (!), right eigenvectors, 
damping ratio and elasticity were determined (Caswel 2001). These values revealed 
how population growth rate, stable size distribution, time to reach the stable size 
distribution, and the vital rates with the greatest influence on population growth, each 
varied between the two study sites and among the thre diferent styles of transition 
matrices. (closed, open, and semi-open). Because each 1-year transition matrix was a 
combination of 4 seasonal matrices, the elasticity equation was modified to negate the 
compounding of elements by matrix multiplication. For details on population model 
analysis, se Caswel (2001). The modification to the elasticity equation revealed how 
each element of al of the seasonal matrices proportionaly afected the dominant 
eigenvalue. The elasticity of each seasonal matrix was summed to determine the total 
contribution of any particular matrix element during the entire year. 
 Recruitment into both anemone populations occurred year-round (se Chapter I), 
so recruitment vectors were added to the populations after each season when applicable. 
Therefore, each one-year projection shows population size in March, but did not show the 
seasonal variation. All other matrix analyses were performed without outside 
recruitment, because recruitment values did not afect the results, so, the yearlong 
matrices were used instead of the 4 seasonal matrices.  
 
Results 
 Dominant eigenvalues (finite population growth rate, !) varied widely betwen 
the two examined populations of Bartholomea annulata, and also among the thre 
 
69 
transition matrices (closed, open, and semi-open, Table 3.2A). These diferences in 
eigenvalues revealed to what extent the various posible modes of reproduction and 
recruitment affected population growth rates, because the only diferences between the 
transition matrices were the reproductive values (Table 3.1A, B, C). The closed 
transition matrices representing both the Brewers Bay and Flat Cay anemone populations 
had eigenvalues >1, indicating population growth, whereas the open and semi-open 
transition matrices had eigenvalues <1, revealing that the processes represented by the 
matrices did not cause population growth on their own. The eigenvalues for the open 
model revealed that the transition between size-clases of anemones currently in the 
population were not enough to cause population growth, while the eigenvalues for the 
semi-open model indicate that these processes along with asexual reproduction also were 
not enough to maintain population growth. Eigenvalues for the open and semi-open 
models indicated the apparent importance of outside recruitment for the population 
growth of these anemones. 
 The damping ratio (!), which is the ratio of the dominant eigenvalue to the 2
nd
 
largest eigenvalue in each model, revealed the time required for each population to reach 
the stable-size structure (Table 3.2B). Note that given the current population structure 
and trends at each site, the Brewers Bay population was projected to each a stable-size 
structure in only a few years, while the Flat Cay population was expected to require 10s 
to 100s of years to reach the stable-size structure. This pattern is due largely to the 
relative absence of both large resident anemones, and of large recruits, at Flat Cay 
(Chapter I). The lack of both together at this site further supports the idea that large 
 
70 
residents may be mainly responsible for the production of large recruits through clonal 
replication. 
 The stable size structure of each population revealed the expected ratio of 
individuals in each size-class, if current population trends persist (Table 3.3). The 
population did not have to reach steady state for stable size structure to be reached; 
rather, once stable size structure was reached, if the population is growing or shrinking, 
the proportion of anemones in each size-class remained the same. The expected stable 
size structure for each population was based on the transition matrices for each model, 
therefore outside recruitment, which was incorporated into the recruitment vector, had no 
influence. Therefore, the actual, maximal, and average versions of the open and semi-
open models shared a common size stage structure. When stable size structure was 
reached at Brewers Bay, >50% of the anemones would be in the smallest size-class for 
the closed population, and 38% and 24% for the open and semi-open populations 
respectively. At Flat Cay, an even greater percentage of the populations would be in the 
smallest size-class: >75% in the closed population, 63% in the open population, and 53% 
in the semi-open population. Current population size structure (Table 3.3) difered from 
the expected stable size structure, because time was required for these apparently 
growing populations before the stable size structure could be reached.  
 Elasticity analyses for both closed population models indicated that the smallest 
size-classes had the largest effect on population growth rate (Table 3.4A). Elasticity 
represented which aspects of the transition matrix exerted the greatest proportional 
changes on population growth rate. Thus, a 10% increase in the growth of the smallest 
size-class would increase population growth rate more than a 10% increase in the largest 
 
71 
size-class remaining the same size. The same was true of the open population (Table 
3.4B). At both locations, the smallest individuals had a greater efect on population 
growth rate than did the largest individuals, with the exception of the largest size-class at 
Brewers Bay. The sum of elasticities of the largest individuals at Brewers Bay was 
almost as large as the sum of elasticities of the smallest anemones (.089 and .097 
respectively). This indicated that having both the largest and the smallest anemones in 
the population was crucial to maintaining the open population. The semi-open 
population, which included asexual reproduction in the 3 largest size-classes, painted a 
diferent picture than the other 2 models (Table 3.4C). In this case, in the Brewers Bay 
population, the elasticities were greatest for shrinkage of the largest anemones. This was 
because the shrinkage value in the transition matrices included asexual reproduction (See 
Table 3.1C). This was not true for the semi-open model for Flat Cay. At Flat Cay, there 
were no anemones in the largest size-class and very few in the 75-100 cm
2
 size-class, 
resulting in very small transitions to these size-classes, and small elasticities. For the 
semi-open model at Flat Cay, the elasticities indicated that stasis in the 50-75 cm
2
 size-
class, and growth of the 25-50 cm
2
 size class, both had the largest influence on 
population growth rate at this site. 
 The closed population model projected that anemone populations would continue 
to grow at both Brewers Bay and at Flat Cay (Fig. 3.1A and Table 3.5A and B). The 30-
year population projections showed that each closed population would grow much larger 
than either site could maintain. The carrying capacity of these reef sites currently is 
unknown for these populations, but it is expected to be much less than the unrestricted 
population sizes projected here. 
 
72 
 The open population model projected the Brewers Bay population to decrease to 
~29% of its original population size and the Flat Cay population to decrease to ~10% of 
the original population after 1 year, without recruitment. This pattern was very diferent 
from the closed population model that projected large population growth each year, and 
indicated that recruitment/reproduction played a large role in maintaining population size. 
This became more apparent when the semi-open model was taken into account. In the 
semi-open model, the Brewers Bay population was projected to decrease to ~71% of the 
original population size, while the Flat Cay population was projected to decrease to ~20% 
of the original population size after one year, without outside, sexual recruitment. 
Though neither population decreased as fast as the in the open population model both 
populations would eventually go to zero (Table 3.2C).  
 The open population model for Brewers Bay, using the observed recruitment 
numbers, showed that the population becomes stable after a 4-year growth period at a 
population size of about 151 anemones (Fig. 3.1B and Table 3.5C). Integrating variation 
into the model changed the maximum population size. For the average model (where 
observed recruitment is treated as ! of potential), a true steady state would never be 
reached but more of a quasi-steady state.  This was because of the variable nature of the 
model, in which recruitment could vary from zero to twice that of observed levels. The 
maximum and minimum population sizes after four years were projected to 160 and 143 
anemones (Fig. 3.1B). Thus, if this population did not experience recruitment failure for 
an extended period, it would stabilize and become similar in size to that projected by the 
model where the actual recruitment values were used. The maximal population model 
(where observed recruitment is treated as the maximum potential recruitment) reached a 
 
73 
quasi-steady state value at a much smaller population size than did the average model 
(Fig. 3.1B). In this case, after a 4-year growth period, the maximum population size was 
projected to be about 81 anemones, with a minimum of 70 anemones. 
 The semi-open population model for Brewers Bay projected a 20-year growth 
period before the population stabilized at around 269 anemones (Fig. 3.1C and Table 
3.5E). The average model projected a range of 264-276 anemones, much greater than 
values projected from the maximal model of 133-138 anemones in the population. After 
one year of population change at this site, the observed population size was 122 
anemones, much larger than that projected by the open-maximal population model, but 
smaller than the expected steady state projected from the open-average and open-
observed recruitment models. When observed rates of recruitment were used, there was a 
4-year and 20-year growth period for the open and semi-open models respectively, before 
the population size stabilized (Fig. 3.1B and 3.1C). Thus, if current population size does 
not change, the maximal semi-open population model appeared to most closely project 
the population size of these anemones. 
 Population projection models for the sea anemones at the Flat Cay site yielded 
similar paterns to those for Brewers Bay. The open population model, using observed 
recruitment rates, stabilized after 3 years with a maximum population size of 83 
anemones. The average model projected a range of 83-102 anemones, and the maximal 
model projected a range of 40-48 anemones (Fig. 3.1D and Table 3.5D). These 
population sizes did not difer much from those produced by the semi-open model, which 
projected population stabilization after 4 years at about 91 anemones, using observed 
recruitment rates. The average semi-open model for Flat Cay projected 83-97 anemones, 
 
74 
while the maximal model projected 43-50 anemones in the population (Fig. 3.1E and 
Table 3.5F). The open and semi-open models for Flat Cay all produced similar projected 
population sizes, because few large anemones occurred in this population and even fewer 
anemones recruited to the population at large body size (i.e.: products of asexual 
cloning), in contrast to the reproductive patterns at Brewers Bay.  Therefore, asexual 
reproductive rates, which varied among the above 3 models, exerted litle influence on 
maximal population size at Flat Cay. Currently, population size at Flat Cay is 77 
anemones, which is midway between future sizes projected by the average and maximal 
models above. A short, 3-year period of growth is expected before the anemone 
population at Flat Cay stabilizes. At that point, it would be possible to determine how 
accurately theses models project actual short-term population trends. 
 
Discusion 
 We show here that based on our assumptions and given current trends in 
population growth and recruitment, the two examined populations of the corkscrew 
anemone Bartholomea annulata in the US Virgin Islands are expected to continue to 
grow and to stabilize in size over the next 30 years. Both are highly dynamic, and exhibit 
rapid rates of transition among size-classes and of mortality of individuals (Chapter I). 
Thus, these anemone populations depend on rapid influxes of a large number of small 
individuals, in the form of a steady supply of new recruits.  
 Commercial fishing for the aquarium trade is a large, profitable industry that is 
only beginning to incorporate scientifically-based regulations to protect ornamental 
organisms from over-harvesting (Chiappone et al. 2001, LeGore et al. 2005). 
 
75 
Unfortunately, non-coral invertebrates often are overlooked in regulations aimed at 
maintaining sustainable harvest of ornamental reef organisms (MyFCW.com 2008, Rule 
68B-42, F.A.C.). Regulatory agencies, and indeed the fishers themselves, appear to 
assume that populations of non-coral invertebrates are sustainable even under intense 
fishing pressure (Shuman et al. 2005). Our application of seven types of population 
models to each of two populations of the large Caribbean sea anemone B. annulata reveal 
that given current non-fished conditions in the US Virgin Islands, anemones populations 
at both sites are projected to thrive. The open and semi-open population models also 
suggest that outside recruitment appears to play a large role in maintaining the stability of 
these populations. 
 If outside recruitment decreases or fails completely for even 1 year, then these 
anemone populations are expected to decline at a rapid rate, because of the observed high 
mortality rates in all size classes (Chapter I). Thus, due to the rapid turnover of these 
populations, recruitment must remain high in order to make up for the rapid and constant 
loss of individuals from the populations. Elasticity analysis of all models at Flat Cay, and 
of the closed and open models at Brewers Bay, reveals that the growth and survival of the 
smallest anemones have the greatest effect on population growth rates. Population 
growth rates in both the open and semi-open models is <<1, which represents no change 
in population size, at both study locations. Thus, in fished populations, ensuring the 
growth and survival of the small anemones alone may not be enough to cause population 
growth and stability. Protection of a steady recruitment source, in addition to ensuring 
the high survival of small anemones, may be needed to maintain sustainable populations 
of this highly-prized anemone. For successful sexual reproduction, individuals of B. 
 
76 
annulata, as in other broadcast spawners, need to reach a minimum critical abundance for 
adequate fertilization of gametes (Levitan et al. 1992, Quinn et al. 1993, Levitan 2004). 
Therefore, to maintain anemone populations in fished environments, high levels of 
outside recruitment are necessary. This requires large nearby source populations for the 
arrival of planktonic larvae.  
 The models presented here difer from some recent stage-based models of reef 
coral populations (Hughes 1984, Fong and Glynn 1998), in that they do not incorporate 
the potential impacts of large physical disturbances such as hurricanes or flooding. The 
reef sites that we examined on St. Thomas have experienced several hurricanes in recent 
decades (Bythell et al. 1993, Edmunds 2002). Thus, the population trends modeled here 
likely wil be interrupted by storms and other disturbances that wil reduce population 
sizes at unpredictable time intervals. However, these models allow projection of 
potential recovery rates of these anemone populations following hurricanes and other 
disturbances, given the size and structure of surviving populations after each type of 
disturbance. Based on observed demographic patterns for the corkscrew anemone B. 
annulata (Chapter I), and the model projections presented here, we predict that 
populations of this species wil recover fairly rapidly from disturbances if a source 
population remains nearby. The open and semi-open models project that even if the 2 St. 
Thomas sites contain zero anemones, the populations could recover to current size in <3 
years via an influx of planktonic recruits. The closed model projects longer recovery 
times (up to 25 years at Brewers Bay if the population is reduced to only 10 anemone in 
the smallest size-class, and 5 years at Flat Cay), with the populations never recovering if 
 
77 
they crash to zero, because in this model, the populations rely entirely on self-
recruitment.  
 Based on the above data, we recommend specific regulatory measures to ensure a 
sustainable ornamental fishery on these important Caribbean anemones. These 
regulations also wil protect the obligate cleaner shrimps that associate with these sea 
anemones, and thus contribute to the maintenance of sustainable stocks of these in-
demand ornamental crustaceans (LeGore et al. 2005). Firstly, a minimum anemone body 
size of about 50 cm
2
 TCSA (~4 cm tentacle crown diameter) for collection wil ensure 
that the smallest individuals in these populations (the ones that contribute the most to 
population growth and survival) wil not be removed. Secondly, we recommend that 
anemone collection be banned altogether in selected reef areas near each fished area. 
High rates of juvenile recruitment depend on high levels of sexual reproduction in the 
local adult population, because self-recruitment appears to be the rule for most coral reef 
organisms (Hughes et al. 2000). The creation of marine protected areas near open fished 
areas, or at least nearby areas where anemone fishing is prohibited, wil allow the 
survival of large adult individuals in nearby populations. This wil maintain adequate 
sexual reproduction and local recruitment. Implementation of both these recommended 
measures (minimum collection size together with the nearby unfished areas) wil enhance 
both anemone recruitment and survival rates, and support stable populations of B. 
annulata as the basis of a sustainable fishery (Quinn et al. 1993). Implementation of 
these regulatory measures is expected to produce 3 synergistic effects: (1) creation of 
long-term sustainable collecting sites for ornamental fishers of sea anemones and 
associated invertebrates such as cleaner shrimp, (2) prevention of local extinction of 
 
78 
corkscrew anemones on Caribbean coral reefs, which appears to have already occurred in 
some parts of Florida due to overfishing (Chiappone et al. 2001), and (3) positive cascade 
effects on the diversity and abundance of large reef fishes, due to the maintenance of 
populations of anemone-based cleaner shrimps and thus of fish cleaning stations in 
adequately-regulated reef areas. The results of this research apply only to populations of 
giant sea anemones with similar reproductive strategies to B. annulata and we do not 
recommend extrapolation to mainly clonally reproducing populations such as those of 
Aiptasia pallida that may behave very diferently in response to collection pressure. 
 We conclude that the application of size-based population modeling is an 
effective tool for projection of giant sea anemone population sizes, and that elasticity 
analysis can reveal the crucial life stages that most impact the growth rates of these 
populations. The use of these tools has the potential to provide a more scientific basis for 
the sustainable management of the large ornamental fishery based on these spectacular 
reef organisms.
 
79 
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84 
Table 3.1. Transition matrices for the sea anemone Bartholomea annulata in 3 types of 
population models (A, B, C). The sum of a column is equal to the survival of that size-
class of anemones. (G) represents growth, (S) represents shrinkage, and (L) represents 
remaining in the same size-class (stasis). 
A. Open 
 
L
11 
S
12 
S
13 
S
14 
S
15 
G
21 
L
22 
S
23 
S
24 
S
25 
G
31 
G
32 
L
33 
S
34 
S
35 
G
41 
G
42 
G
43 
L
44 
S
45 
G
51 
G
52 
G
53 
G
54 
L
55 
 
B. Closed 
L
11 
S
12
+F
12 
S
13
+F
13 
S
14
+F
14 
S
15
+F
15 
G
21 
L
22
+F
22 
S
23
+F
23 
S
24
+F
24 
S
25
+F
25 
G
31 
G
32
+F
32 
L
33
+F
33 
S
34
+F
34 
S
35
+F
35 
G
41 
G
42
+F
42 
G
43
+F
43 
L
44
+F
44 
S
45
+F
45 
G
51 
G
52
+F
52 
G
53
+F
53 
G
54
+F
54 
L
55
+F
55 
 
C. Semi-open 
 
L
11 
S
12 
S
13 
S
14 
S
15 
G
21 
L
22 
S
23 
S
24 
S
25 
G
31 
G
32 
L
33
+F
33 
S
34
+F
34 
S
35
+F
35 
G
41 
G
42 
G
43
+F
43 
L
44
+F
44 
S
45
+F
45 
G
51 
G
52 
G
53
+F
53 
G
54
+F
54 
L
55
+F
55 
 
85 
Table 3.2. Variation in A. dominant eigenvalues (finite population growth rate, !), B. 
Time in years to reach stable size structure, and C. time until populations reduce to zero 
without outside recruitment, for populations of the sea anemone Bartholomea annulata 
among 3 types of population matrices (closed, open, and semi-open) at 2 coral reef sites 
(Brewers Bay and Flat Cay). Dominant eigenvalues >1 represent population growth, and 
<1 represent population shrinkage. 
A. 
 Closed Population Open Population Semi-open Population 
Brewers Bay 1.104 0.28 0.707 
Flat Cay 1.381 0.101 0.206 
 
B. 
 Closed Population Open Population Semi-open Population 
Brewers Bay 3.53 7.35 1.10 
Flat Cay 975.19 138.74 25.17 
 
C. 
 Closed Model Open Model Semi-open Model 
Brewers Bay N/A 4 Years 15 Years 
Flat Cay N/A 3 Years 4 years 
  
 
 
86 
Table 3.3. Proportion of individuals of the sea anemone Bartholomea annulata in each 
size-class after projected stable-size structure has been reached. Actual observed 
population size-structure during the March 2007 census also is given for comparison. 
  
0-25 cm
2
 25-50 cm
2 
50-75 cm
2 
75-10 cm
2 
>10 cm
2 
Brewers Bay Closed Population .536 .152 .125 .093 .094 
 Open Population .380 .148 .145 .146 .181 
 Semi-open Population .241 .101 .218 .184 .256 
 March 207 Population .514 .284 .073 .073 .05 
       
Flat Cay Closed Population .754 .168 .052 .031 0 
 Open Population .632 .278 .059 .031 0 
 Semi-open Population .534 .241 .125 .10 0 
 March 207 Population .736 .170 .075 .019 0 
 
 
87 
Table 3.4. Elasticity values of each size class of individuals (columns) in populations of 
the sea anemone Bartholomea annulata at 2 coral reef sites (Brewers Bay and Flat Cay). 
Bold numbers represent the greatest elasticity values in each table. A. Closed 
populations, bold represents elasticities >0.5. B. Open populations, bold represents 
elasticities >0.01. C. Semi-open populations, bold represents elasticities >0.1.  
A. 
Closed Population 
 
0-25 cm
2 
25-50 cm
2 
50-75 cm
2 
75-10 cm
2 
>10 cm
2 
Brewers Bay Growth .701 .615 .302 .096  
 Loop .648 .379 .23 .141 .186 
 Shrinkage  .253 .346 .360 .630 
       
Flat Cay Growth 1.29 1.065 .05 0  
 Loop .607 2.094 .24 0 0 
 Shrinkage  .814 .910 .634 0 
 
B. 
Open Population 
 
0-25 cm
2 
25-50 cm
2 
50-75 cm
2 
75-10 cm
2 
>10 cm
2 
Brewers Bay Growth .031 .035 .014 .010  
 Loop .06 .019 .010 .09 .043 
 Shrinkage  .015 .021 .016 .046 
       
Flat Cay Growth .06 .06 0 0  
 Loop .09 .08 .01 0 0 
 Shrinkage  .04 .04 .04 0 
 
 
88 
C. 
Semi-open 
Population 
 
0-25 cm
2 
25-50 cm
2 
50-75 cm
2 
75-10 cm
2 
>10 cm
2 
Brewers Bay Growth .080 .15 .218 .121  
 Loop .096 .050 .139 .14 .036 
 Shrinkage  .026 .102 .141 .392 
       
Flat Cay Growth .015 .027 .012 0  
 Loop .015 .021 .031 0 0 
 Shrinkage  .07 .018 ,024 0 
 
Table 3.5. Three types of transition matrices (closed, open, semi-open) used to construct 
population models for the sea anemone Bartholomea annulata at each of 2 coral reef sites 
(Brewers Bay and Flat Cay).  
Table 10 A. Brewers Bay Closed Matrix B. Flat Cay Closed Matrix 
 0-25 
cm
2 
25.1-50 
cm
2 
50.1-75 
cm
2 
75.1-10 
cm
2 
>10 
cm
2 
0-25 
cm
2 
25.1-50 
cm
2 
50.1-75 
cm
2 
75.1-10 
cm
2 
>10 
cm
2 
0-25 cm
2
 .250 .721 .902 1.154 1.363 .041 2.786 2.901 4.508 3.236 
25.1-50 cm
2
 .070 .204 .256 .327 .386 .092 .612 .649 1.01 .720 
50.1-75 cm
2
 .05 .171 .214 .272 .323 .028 .191 .201 .31 .28 
75.1-10 cm
2
 .042 .127 .159 .202 .239 .014 .093 .010 .156 .28 
>10 cm
2
 .041 .129 .162 .206 .245 0 0 0 0 0 
 C. Brewers Bay Open Matrix D. Flat Cay Closed Matrix 
0-25 cm
2
 .18 .103 .091 .127 .098 .045 .098 .068 .136 0 
25.1-50 cm
2
 .040 .041 .039 .052 .04 .019 .043 .036 .072 0 
50.1-75 cm
2
 .032 .042 .043 .05 .052 .04 .09 .06 .012 0 
75.1-10 cm
2
 .032 .042 .043 .05 .052 .02 .05 .04 .09 0 
>10 cm
2
 .035 .053 .05 .072 .071 0 0 0 0 0 
 E. Brewers Bay Semi-open Matrix F. Flat Cay Semi-open Matrix 
0-25 cm
2
 .126 .141 .151 .209 .214 .052 .180 .136 .26 .12 
25.1-50 cm
2
 .04 .058 .065 .089 .096 .02 .079 .065 .10 .047 
50.1-75 cm
2
 .059 .120 .146 .195 .234 .010 .046 .03 .054 .032 
75.1-10 cm
2
 .056 .103 .124 .165 .193 .07 .04 .028 .046 .025 
>10 cm
2
 .067 .140 .172 .230 .275 0 0 0 0 0 
 
 
 
 
89 
Figure Legends 
 
Fig. 3.1. 30-year projections for 3 types of size-based matrix models of populations of 
the sea anemone Bartholomea annulata at 2 coral reef sites (Brewers Bay and Flat Cay): 
A. Closed models for both reef sites. Anemone populations are projected to grow much 
larger than carrying capacity would allow. B. Open models at Brewers Bay. C. Semi-
open models at Brewers Bay. D. Open models at Flat Cay. E. Semi-open models at Flat 
Cay. For all open and semi-open models, population sizes projected by the models that 
use actual recruitment and average values are slightly larger than current levels, while the 
maximal model projects anemone populations to be smaller. Average and maximal 
models are shown as means +/- SEM of N=30 replicates. 
 
 
90 
 
Fig. 3.1A 
 
91 
 
Fig. 3.1B, C
 
92 
 
Fig. 3.1D, E