© 1991 by The Society for Integrative and Comparative Biology
Indirect Effects in Experimental Studies of Marine Soft-Sediment Communities1
University of Georgia Marine Institute Sapelo Island, Georgia 31327
Most experimental studies that deal with the effects of biotic interactions in marine soft sediments are designed to examine the direct effects of one species (or group of species) on some subset of the community. However, species within a community influence one another through a complex web comprising both direct and indirect effects. Ignoring this complexity in the development of hypotheses and experimental designs will likely lead to unexpected or conflicting findings. Few studies of marine soft-sediment communities have emphasized indirect effects and even fewer have included experimental designs capable of testing for them. To illustrate the potential importance of indirect effects in marine soft sediments, I provide several examples from the literature and describe the type of experimental design required to demonstrate a simple indirect effect involving three species. Perspective on indirect effects in a particular community changes as more information is collected about individual species and their effects. The influence of one species or guild may be confounded by that of another and even effects expected to be strong may appear weak or nonexistent as a result of unidentified indirect effects. Recognizing indirect effects in soft-sediment communities may help to explain apparent paradoxical results in past experiments and provide an improved template for the design of future experiments.