Community ecology of gorgonians and population modeling of Pseudopterogorgia acerosa in Biscayne Bay, Florida

Biscayne Bay is recognized as an integral part of the South Florida marine ecosystem. Numerous fish and invertebrate species utilize its various habitats, and the system supports a commercial bait shrimp fishery. Upland water management practices (including the Comprehensive Everglades Restoration Project) will alter its hydrology and impact biota. The two principal benthic habitats within the Bay are seagrass meadows and hardbottom substrate (supports gorgonian and scleractinian corals, sponges and rhizophytic algae). Baseline data are sparse for hardbottom and gorgonian communities within the Bay. This dissertation addresses two aspects of gorgonian biology within the Bay: gorgonian community structure and simulation modeling of Pseudopterogorgia acerosa population dynamics. Four species dominate the gorgonian community, with eight additional minor species. Species diversity and colony density are relatively low compared to reefs and other nearshore hardbottom habitats in the Caribbean, and the size structure of three of the four most common species suggest a recent (5--10 years) lack of recruitment. Principal Components and Canonical Correspondence Analyses indicate three environmental factors influence gorgonian abundance patterns: current speed, water depth, and sediment depth. Modeling analyses investigate the impact of varying recruitment patterns and increased mortality on P. acerosa population abundance and size structure. Modeling the populations separately proves more effective than modeling them as a single unity. Without recruitment all populations decline geometrically at intrinsic rates of increase less than one. The addition of recruits prolongs population duration and shifts size structure towards more small individuals. Increased mortality rates (e.g., from shrimp trawling) reduce the relative amount of large individuals and could have serious implications for population fecundity. In addition, analyses of recruitment onto bare sites indicate that the populations may establish themselves relatively quickly, albeit at lower abundances than currently observed.