Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Rochelle D. Seitz


Anthropogenic stressors such as habitat loss, extreme weather events, and acidification can change predator-prey interactions. An understanding of the mechanisms by which these stressors impact predator-prey interactions may elucidate the fate of bivalves in the face of global change. My dissertation research informs management of marine resources in Chesapeake Bay, which has experienced substantial seagrass and oyster reef loss, increased storm activity, and combined estuarine and atmospheric CO2 acidification. In my dissertation, I used field survey data, field caging experiments, laboratory mesocosm experiments, time-series analysis, and density-dependent mathematical models to assess the role of habitat, major storm events, acidification, and predators on bivalve distribution in lower Chesapeake Bay, with a special focus on the commercially important, thin-shelled clam species Mya arenaria, which has declined significantly in the past few decades.;In field surveys, seagrass supported one additional bivalve functional group (based on bivalve morphology and feeding mode) than all other habitat types, and bivalve diversity was 2754% higher in seagrass than in shell hash, oyster shell, coarse sand, and detrital mud habitats. The odds of finding M arenaria were higher in seagrass than in all other habitats. Predators likely consumed seasonal pulses of juveniles each year. In field caging experiments, blue crabs Callinectes sapidus were likely responsible for most of the mortality of juvenile M arenaria, which was 76.6% higher for caged juveniles than for uncaged individuals over 5 d. In mesocosm feeding trials, M arenaria maintained a low-density refuge from predation by blue crabs, and had higher survival in oyster shell or shell habitats as compared to sand or seagrass habitats. Time series analysis suggested M arenaria was subjected to a storm-driven phase shift to low abundance in 1972, which has been maintained by blue crab predation. Density-dependent predator-prey models parameterized with data from laboratory and field experiments confirmed the presence of a coexistence steady state at low densities of M arenaria, providing the theoretical proof-of-concept that M arenaria can exist in a low-density stable state in the face of blue crab predation. Acidification altered behavior of both predator (C. sapidus) and prey (M arenaria), resulting in no net change in proportional mortality of clams between acidified and control feeding trials.;My dissertation examined multiple lines of evidence to address the importance of structured habitat, extreme weather events, and acidification in the mediation of predator-prey dynamics. For the crab-bivalve predator-prey interactions examined here, predation exacerbated the effects of some anthropogenic stressors (habitat loss, extreme weather events) and ameliorated the impacts of other stressors (acidification) on bivalve prey. An understanding of density-dependent predation is a necessary component of an adaptive management strategy that can cope with climate change.



© The Author