In recent decades, both oyster and blue crab populations have suffered significant declines often attributed to coastal development and overfishing. However, little is known about the biotic species interactions, such as trophic cascades, that could affect the stability and resilience of oyster reef communities and in consequence promote their recovery. Trophic cascades are well known in other systems (i.e. kelp forests and coral reefs) for their ability to structure and stabilize communities and the role of non-consumptive effects (NCEs) in these trophic cascades is increasingly recognized as driving many of these interactions. However, since NCEs are often context dependent upon risk assessment of the predator, current research is focused on what aspects of predator variation may influence the magnitude of NCEs in trophic cascades. One aspect that has yet to be considered is that of predator size. Predator size is often indicative of risk and yet it is unknown if this is translated in chemical cues which often drive NCEs.

Results/Conclusions

Our research examines a trophic cascade between blue crabs, mud crabs, and their shared oyster prey in order to determine how predator size affects the magnitude of NCEs. In this cascade, blue crabs may positively affect oyster populations by suppressing the foraging activity of mud crabs through NCEs. Predation experiments between mud crabs and blue crabs demonstrate that blue crabs are effective predators on mud crabs and that predation levels are dependent on both predator size and habitat complexity. Additionally, mesocosm experiments with caged blue crabs establish that blue crabs have a non-consumptive effect on mud crabs and suppress both their presence on oyster reefs and their oyster consumption. The magnitude of this effect is a function of blue crab size (large predators produce the largest NCEs), and predator diet, whereby a diet of crushed conspecifics elicits the greatest response from mud crabs. Long term field experiments are examining the effects of both mud crabs and blue crabs on oyster recruitment and survival. Preliminary results indicate that cues from blue crabs increase oyster recruitment. The results of these experiments have consequences for understanding both NCEs and reef resilience.