The Fouling Community at Beaufort, North Carolina: A Study in Stability

The stability of natural communities can only be studied by asking, "How does a local resident adult assemblage respond to the perturbations it experiences?" One must measure perturbations directly and independently of the community response. One must be alert to perturbations which potentially or actually add to, as well as subtract from, the resident adult assemblage. The appropriate time scale will depend on the perturbation frequency and the community response, if any. This approach to stability is applied to the fouling community at Beaufort, North Carolina. Multiple stable points, resident assemblages resistant to recruitment (Sutherland 1974), are common and are evidence for persistence stability. However, most eventually disappear because of continued recruitment of other species, overgrowth, sloughing off, or senility. Thus there is ample evidence for instability in the community (Sutherland and Karlson 1977) especially if one compares the species composition of winter assemblages. However, with the Styela assemblage as a reference, the community is stable over many years. Styela inhibits recruitment by other species when present and reinvades in spring after sloughing off the previous fall. This is analogous to the mussel communities studied by Dayton (1971), Paine (1966, 1974), and Menge (1976) where patches of mussels are continuously removed by a variety of disturbances, but eventually reinvade. Evidence for stability and instability can be found in all communities, depending on the reference assemblage, specific perturbation, and time scale. One must be content to ask more specific questions than, "Is this community stable?"