Thus, blue crab behavior in the field, either in terms of foraging or distribution, must be different than that of individual crabs in isolation. Analysis of our behavioral data is ongoing and may shed light on the cause of this difference. A second project investigated how refuges from predation modify both the direct and indirect effects of interspecific interactions in an estuarine community of moderate trophic complexity. Although the effects of refuge are well documented for simple communities, little is known about its effects on complex trophic interactions in more diverse communities. Because of indirect effects, the impacts of refuge in more diverse communities are not easily predicted from simpler systems.
Indirect effects occur when the interaction between two species is influenced by a third species.
Mathematical models suggest that indirect effects can greatly affect the stability and complexity of species interactions within communities, but our current understanding of their importance or of the mechanisms involved is far from complete. I investigated nontrophic indirect effects in seagrass communities, primarily in St. Joseph Bay in the northeastern Gulf of Mexico. If changes in pen shell availability affect some species more strongly than others, horse conchs may also indirectly influence community composition. These results suggest Atrina mortality rate, that is, the availability of new shelters, will be determined primarily by horse conch abundance rather than Atrina density. Since the fishes use the shells not only for shelter but also as a site for reproduction , the gastropod predator may influence both local abundance and reproductive output, which potentially affects individual fitness.