A CORAL-REEF ECOSYSTEM-FISHERIES MODEL - IMPACTS OF FISHING INTENSITY AND CATCH SELECTION ON REEF STRUCTURE AND PROCESSES

An aggregated energy-based coral reef simulation model was developed and used to perform fishing experiments where fishing intensity and catch selection were varied. The model is composed of two groups of primary producers (coral and algae), herbivores (herbivorous fishes and sea urchins) and carnivores (piscivores and predators of invertebrates). Gross and net primary production are calculated from coral and algal production and respiration parameters, while the calcium carbonate balance is calculated from deposition by coral and algae and erosion by sea urchins and herbivorous fish. Simulation results indicate that fishing affects the coral reef's ecology and the benefits of the fisheries yield must be weighed against impacts on reef structure and processes. The model predicts that removing all fish groups will eventually result in reef dominance by sea urchins once their predators have been removed. This results in a rapid and dramatic drop in fisheries yields and reduced algal and coral biomass and productivity. Net calcium carbonate deposition is particularly sensitive to the effect of sea urchins or fishermen on living coral. Fishing only piscivores results in low fisheries yields but high reef accretion by indirectly releasing coral from competition with algae. A management strategy of fishing only piscivores and herbivorous fishes results in the highest and most stable fisheries yields. However, under this management strategy, high levels of fishing results in increased algae that competitively exclude coral and produces a temporary reduction in calcium carbonate deposition. But, at the highest algal biomass, calcium carbonate deposition is high and solely attributable to algal deposition. Nonetheless, this form of calcium carbonate deposition may not provide the reef structure required for fish habitat and shoreline protection. It may therefore prove beneficial, over the long term, to keep fishing below this level.