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UBC Theses and Dissertations

Seasonal ecosystem models of the Looe Key National Marine Sanctuary, Florida Venier, Judson McCormick


Five mass-balance trophic models (1 annual and 4 seasonal) were constructed of the Looe Key National Marine Sanctuary ecosystem, Florida, USA using the ECOPATH approach and software package in order to increase our understanding of its, and other coral reefs', general and seasonal function. Input parameters were obtained from published data on Florida and additional coral reef areas. The Looe Key Sanctuary (18 km²) was chosen as a representative reef of the Florida Reef Tract system which runs for 580 km offshore of the Florida Keys and contributes greatly to South Florida's economy. Looe Key receives heavy use by SCUBA divers and snorkelers throughout the year, and contains many habitats and a high diversity of organisms. Modeling the ecosystem provides a way to synthesize available information from the Keys in order to increase our understanding of how these fragile and important ecosystems function, which can contribute to our ability to manage them effectively. The ways that coral reef ecosystem structure and function change seasonally is poorly understood. It is clear that all measured states and rates, such as biomass, primary productivity, coral and fish growth, grazing and recruitment exhibit marked seasonality on reefs throughout the world. In general, the Looe Key ecosystem is large in terms of primary productivity and energy flow. The production at higher trophic levels was found to be strongly dependent upon the secondary production of detritus, from which 75% of all flows originate. The majority of production of most groups is directly consumed within the system and non-predation losses are small. Many groups feed at more than one trophic level which indicates a great degree of interdependency within the system. Compared with other reef systems, the overall maturity of Looe Key was intermediate, although the two Caribbean systems (Looe Key and the USVI) appeared more mature than those modeled in the Pacific. Apparently Pacific reefs have more specialized organisms than those in the Caribbean. Looe Key seems to be relatively large in terms of energy flow when compared with other reef systems, and transfers this energy up the food web more efficiently. Secondary production by detritus was important in most systems compared, and thus may be a general feature of coral reefs throughout the world. When seasonal models of Looe Key were compared, total system flow was much larger in summer, when biomasses were higher, than in winter. The system was also autotrophic during the warmer seasons and heterotrophic during winter, and was supported throughout the winter by detritus, which accumulated during the more productive seasons. A simulation routine was also run on the Looe Key ecosystem to investigate the changes in biomass which would result from the introduction of spearfishing on the top predators. The outputs suggest that the total system biomass would not change, but that a shift in its distribution to small carnivores and large herbivores would occur. This change at Looe Key simulated by the model is consistent with reports of what the system was like before spearfishing was outlawed in 1981.

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