Mobile Predators and the Structure of Marine Intertidal Communities

Field experiments and quantitative sampling have been very productive in demonstrating the relative importance of physical factors, competition, and predation in structuring various intertidal communities. The authors address a small, but general, methodological problem that may have large consequences for interpretations of how predators alter intertidal communities. Specifically, the effects on community structure of such highly mobile intermittent predators as crabs, fishes, and birds are hard to demonstrate and easy to overlook or misinterpret, but assuming them to be unimportant may perpetuate oversimplified models of community interactions. The authors illustrate, using evidence of their own and from the literature, how this problem may apply in a particular well-studied situation, and question the assumption that Thais lapillus is the only significant predator of mid-intertidal rocky shores in New England. The authors also indicate approaches for resolving the problem and implications of such work.