PREDATOR-PREY RELATIONSHIPS BETWEEN CRASSOSTREA VIRGINICA AND SEVERAL SPECIES OF CRAB AFFECT OYSTER REEF FUNCTION

Direct and indirect effects resulting from predator-prey interactions can affect ecosystem function. Understanding these relationships has been a central focus of community ecology for more than 50 years. However, human impacts on ecosystems during this period may have altered these relationships. Here I assess important impacts of ocean acidification, ocean warming, and land-use change on the predator-prey relationships between the oyster, Crassostrea virginica, and several species of crab. Calcifying marine taxa have been shown to respond differently to ocean acidification. Bivalves typically show more severe reductions in net calcification than the decapods that prey on them. This study found C. virginica and the crab, Panopeus herbstii, had generally reduced net calcification with decreasing calcite saturation states. However, both species maintained positive net calcification in undersaturated calcite conditions. In experiments, acidification significantly reduced the consumption rate of C. virginica by P. herbstii. Differences in net calcification did not explain consumption rates, rather behavioral change, manifest as reduced prey handling and persistence of the predator, were the likely cause. Ocean warming is driving pole-ward shifts in the ranges of numerous species, leading to the formation of novel communities. The stone crab, Menippe mercenaria, is one such species, but little is known about its ecology and thus its like impact on ecosystems in its new range. My data suggest that crabs between 70 and 90 mm are likely to have the largest effect on intertidal oyster reefs due to higher consumption rates and an ability to consume all sizes of oyster. Smaller crabs are limited by the size of oyster they can consume and larger crabs demonstrated less interest in oyster as a prey item. Land-use change and accompanying habitat loss has driven increased interest in estuarine ecosystem services and functions. C. virginica relies on filtration to provide its outsized contribution to estuarine ecosystem function and services. Other species of bivalves reduce their filtration rates to reduce their predation exposure. However, C. virginica showed no such behavior in the presence of two common crab predators. This research highlights the dynamism of predator-prey relationships and their important role in current and future ecosystem function.Doctor of Philosoph