Environmental Controls on Predator and Prey Body Size in the Northern Gulf of Mexico

The Mississippi River delivers vast quantities of nutrient-rich freshwater to the northern Gulf of Mexico, fueling primary productivity in the coastal zone. Aerobic decomposition of these phytoplankton blooms has resulted in one of the most extensive dead zones on Earth. In contrast, primary productivity and hypoxia are more limited in the northeastern Gulf, where coastal environments are fed by smaller watersheds. How do environmental factors such as primary productivity, oxygen availability, and sea surface temperature shape coastal food webs? Here, we investigate environmental correlates of predator and prey body size in benthic mollusks using Holocene death assemblages. Results of linear mixed effects models indicate that bivalve size and the frequency of drilling predation are both influenced by dissolved oxygen concentrations; bivalve size increases and drilling frequency decreases with declining oxygen levels. Sea surface temperature is positively associated with predator and prey size, whereas net primary productivity has little effect on the size of predators or prey. Predator-to-prey size ratios were not significantly associated with any of the environmental factors considered. Larger bivalves found in oxygen-limited areas may be due to decreased predation pressure, resulting in greater prey longevity. Warmer waters with sufficient dissolved oxygen may also provide suitable growth conditions to increase the size of bivalves and predatory gastropods. Holocene death assemblages can be used to test long-standing hypotheses regarding environmental controls on predator-prey body size distributions through geologic time and provide baselines for assessing the ongoing effects of anthropogenic eutrophication and warming on coastal food webs.