Meeting Abstract

2.2  Saturday, Jan. 4 08:15  Top-down Control by Bonnethead Sharks in Oyster Reef Communities Through Consumptive and Non-Consumptive Effects. HOLMES, Z.C.*; BYERS, J.E.; MALEK, J. ; The University of Georgia; The University of Georgia; The University of Georgia zholmes9@uga.edu

The eastern oysters (Crassostrea virginica) along the Atlantic coast are an important foundational species upon which many estuarine species are dependent for food and structure. Bonnethead sharks (Sphyrna tiburo) are the most abundant fish by biomass within some southeastern estuaries and are known to be voracious predators of blue crabs. We conducted a replicated mesocosm experiment to examine how bonnethead sharks influence crab mortality and foraging behavior and how these effects on the crabs trickled down to affect species lower on the food chain, especially juvenile oysters. Our mesocosm study showed that sharks significantly impact juvenile oyster survival, by reducing blue crab abundance and foraging. Bonnetheads however had little effect on mud crab predation of oysters, with substantial quantities of oysters eaten even in the presence of sharks. We also quantified predation rates of crabs in field settings both on and away from oyster reefs. Our results indicate that crab loss is extremely high away from oyster reefs, often approaching 100% in a 12 hour period. These results indicate that bonnethead presence in oyster reef communities is a significant driver of blue crab behavior, with likely implications for other oyster reef community species.