Complex Predator‐Prey Interactions within an Estuarine Benthic Community

Abstract

Indirect predator—prey interactions have been suggested to be important in a variety of communities. However, we still understand little about the factors determining the relative importance of indirect and direct effects of predation or what forms indirect predator—prey interactions may take. We examined the direct effects of predation by an omnivorous grass shrimp. Palaemonetes pugio, and the indirect effects for prey species of interactions between this shrimp and other predators in an estuarine benthic community. Direct and indirect effects of predation were examined in the field using a combination of large— and small—scale enclosure/exclosure experiments. Specific interactions and mechanisms of effects were examined in laboratory predation studies, utilizing both two—species and multi—species systems. Grass shrimp predation reduced the densities of a variety of benthic fauna, but the effects varied seasonally and with prey size. Interactions between grass shrimp and other predators took two forms: reduction of an infaunal predator by shrimp predation and predation on grass shrimp by fish. Both types of interactions had a mixed effect on lower trophic levels, with enhancement of certain benthic prey and no effect on other species. Interactions between grass shrimp and their fish predators resulted in changes in shrimp distribution independent of changes in shrimp abundance, creating spatial refungia for shrimp prey. The dynamics of indirect interactions in this community are strongly affected by the omnivorous nature of the major predators. Our results emphasize the general importance of omnivory in regulating predator—prey interactions and in predicting the relative importance of indirect predator effects.