Environmental tolerance and reproduction of Florida false corals Ricordea florida (Anthozoa: Corallimorpharia): Implications for ornamental fisheries management
Type of DegreePhD Dissertation
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In the aquarium trade, corallimorpharians are commonly known as false corals or mushroom corals, but little is known about the biology of most species. Some species of corallimorpharians are dominant competitors for space on marine benthos, and they have become increasingly popular organisms in the ornamental aquarium trade due to high demand among home aquarists, thus representing a high value fishery. In the Florida Keys, USA, the most common corallimorpharian is the Florida false coral Ricordea florida, which has experienced a sharp decline in abundance since ~ 2010. Major goals of this dissertation were to elucidate aspects of the biology and ecology of this species, in order to enhance scientific understanding about potential causes of the declining abundance, and to provide recommendations to support the management of a sustainable fishery on this species. Under controlled laboratory conditions, I determined environmental tolerances of R. florida to solar irradiance and temperature. The experimental results indicate that individuals of this species thrive when exposed to levels of photosynthetically active radiation (PAR) that match those in shaded microhabitats on shallow coral reefs (~ 40-60 µE m-2 s-1). Field observations revealed that polyps of R. florida may depend on their proximity to large upright benthic organisms such as gorgonians and sea fans, to provide adequately shaded habitats on shallow reefs in the Florida Keys. Polyps of R. florida exhibited various signs of physiological stress when exposed to relatively high PAR levels corresponding to those in unshaded shallow reef habitats. Individuals also thrived at fairly wide range of seawater temperatures (~ 22 -31°C), with more extreme temperatures (both cooler and warmer) causing rapid decline in polyp physiological condition including bleaching and followed in some cases by death. Field observations showed that the upper bound of this range (31°C) was exceeded during the hottest months of both study years (2017 and 2018), and that the lower bound of this range (22°C) was exceeded during a cold event in 2010 that killed many Florida Keys reef organisms. I conclude that increasingly wide seawater temperature fluctuations likely have contributed, and will continue to contribute, to the decline of R. florida populations throughout the shallow Florida Keys. Field monitoring indicated that populations of R. florida have declined significantly since 2010 on some shallow reefs in the middle Florida Keys, but that populations at some sites remained stable during the present study (June 2017 – June 2019). A major physical disturbance in the form of Hurricane Irma (category 4) during September 2017 caused a large decline in monitored populations, which then required ~ 1 year to recover in abundance. Analysis of reproductive processes in R. florida showed that polyps of this species reproduce both sexually and asexually. The sexes are separate, with both male and female polyps spawning gametes for external fertilization in the water column, annually during late June to early July, shortly after the summer solstice, in a similar sexual reproductive pattern to that known for some other corallimorpharian species. Females are larger than males, indicating that they potentially exhibit hermaphroditic protandry. Polyps also are able to replicate clonally to produce aggregations via 3 distinct mechanisms: longitudinal fission, inverse budding, and pedal laceration. During a long-term removal experiment in the middle Florida Keys, aggregations of polyps clonally replicated to complete recover in abundance less than 1 year after the partial removal of 33 to 66% of polyps in each aggregation, such as could be caused by a marine life collector or a natural predator. However, they did not recover in polyp abundance when entire aggregations were removed from the reef, indicating that replenishment solely via recruitment by sexually-produced larvae or planktonic inverse buds is not rapid enough to replenish entire aggregations over the time scale examined here. It is concluded that a sustainable fishery on this species is potentially possible in the Florida Keys, but only if best management practices are observed, including limitation of collection to ≤ ~ 66% of polyps in each aggregation. Populations of R. florida are expected to face increasing threats from other anthropogenic stressors including extreme temperature fluctuations as part of global climate change.