Effects of hypoxia on an estuarine predator-prey interaction: foraging behavior and mutual interference in the blue crab Callinectes sapidus and the infaunal clam prey Mya arenaria

The effects of hypoxia on trophic interactions could vary dramatically depending on whether the benthos is experiencing the onset of a hypoxic event (decreasing dissolved oxygen concentrations from normoxia), or its dissipation (increasing dissolved oxygen concentrations from hypoxia). Predator-prey dynamics between the blue crab Callinectes sapidus and an infaunal clam prey Mya arenaria were examined to assess the impact of hypoxia upon predator foraging rates and prey mortality. Laboratory experiments quantified the behavioral response of M. arenaria to varying dissolved oxygen levels through the analyses of (1) sediment burial depth, and (2) siphon extension above the sediment surface. Moreover, the functional response (relationship between predator consumption rates and prey density) of single and 2 adult blue crabs to 2 densities of M. arenaria (6 and 24 clams tank-1) was examined across 3 dissolved oxygen treatments: (1) normoxia (≥6.0 mg DO l-1); (2) moderate hypoxia (3.0 to 4.0 mg DO l-1), subsequent to clam acclimation at high oxygen conditions (≥6.0 mg DO l-1); and (3) moderate hypoxia (3.0 to 4.0 mg DO l-1), subsequent to clam acclimation at low oxygen conditions (≤1.5 mg DO l-1). M. arenaria sediment burial depth decreased and siphon extension increased during exposure to severe hypoxia. Initiation of moderate hypoxia following normoxia altered blue crab foraging behavior from a destabilizing, type II functional response, to a partially stabilizing, type I functional response. Conversely, blue crabs exhibited a type II functional response under moderate hypoxia subsequent to clam exposure to severe hypoxia. Therefore, low dissolved oxygen concentrations appear to affect the predator-prey interaction between C. sapidus and M. arenaria by either hindering blue crab foraging, or alternatively, increasing clam vulnerability by altering their siphon extension and depth distribution within the sediment column. Moreover, the inclusion of a second blue crab in experimental trials further modified functional responses through both mutual interference and agonistic behavior or cooperative foraging between predators. The collective results indicate that fluctuations in dissolved oxygen concentrations, as well as both predator and prey density, must be examined jointly to understand their impact upon predator-prey dynamics in marine systems.