This Is AuburnElectronic Theses and Dissertations

Determining the spatial and seasonal influences of microbial community composition and structure from the Hawaiian anchialine ecosystem




Hoffman, Stephanie

Type of Degree

PhD Dissertation


Biological Sciences


Characterized as coastal bodies of water lacking surface connections to the ocean but with subterranean connections to the ocean and groundwater, habitats belonging to the anchialine ecosystem occur worldwide in primarily tropical latitudes. Such habitats contain tidally fluctuating complex physical and chemical clines and great species richness and endemism. The Hawaiian Archipelago hosts the greatest concentration of anchialine habitats globally, and while the endemic atyid shrimp and keystone grazer Halocaridina rubra has been studied, little work has been conducted on the microbial communities forming the basis of this ecosystem’s food web. Thus, this dissertation seeks to fill the knowledge gap regarding the endemic microbial communities in the Hawaiian anchialine ecosystem, particularly regarding spatial and seasonal influences on community diversity, composition, and structure. Briefly, Chapter 1 introduces the anchialine ecosystem and specific aims of this dissertation. In Chapter 2, environmental factors driving diversity and spatial variation among Hawaiian anchialine microbial communities are explored. Specifically, each sampled habitat was influenced by a unique combination of environmental factors that correlated with correspondingly unique microbial communities. Notably, salinity was the one water chemistry factor with strong explanatory power and influence in driving microbial community structure. Chapter 3 examines seasonality in these Hawaiian anchialine microbial communities across an 18-month period. Although there was evidence that microbial community structure varied across the wet and dry seasons, these changes were minimal overall and the greatest shifts were in relative abundance of oxygenic and anoxygenic phototrophs, with oxygenic phototrophs more abundant during wet seasons and anoxygenic phototrophs during dry seasons. The specific microbial consortia found in the four distinct layers composing the unique orange laminated cyanobacterial-bacterial crusts from select Hawaiian anchialine habitats are discussed in Chapter 4. As with laminated microbial mats from other ecosystems, greater taxonomic richness within the community occurred deeper within the crust structure, with these crusts apparently, and unusually, oxygenated at both their top and bottom surfaces. Therefore, oxygenic phototrophs were most abundant in the top and bottom of the crusts, with anaerobic metabolisms largely confined to the middle two layers. Finally, Chapter 5 discusses the conclusions of the preceding chapters and future research directions.