Do the Metapopulation Dynamics of Estuarine Fishes Influence the Stability of Shelf Ecosystems?

Determining the ecological effects of coastal perturbations on estuarine fish assemblages depends on first determining which fishes are "obligate" to estuaries. That is, if estuaries were removed, which species would be at risk of significant depletion, or even local or regional extirpation? In this context, it appears that about one-fourth of the fish species of the Virginian and Carolinian provinces is estuary-dependent. The large, apparently stochastic fluctuations in the relative abundances of shelf fishes that have been observed may be a function of scale-related, habitat alterations, especially within estuaries: e.g., ecological perturbations caused by the dramatic, fisheries-related demise of oysters and oyster reefs. Because of ecosystem responses to such perturbations, we can not take for granted that the population depletions due to fishing are reversible, as ecosystem alterations that affect fishes may themselves not be readily reversible. It is proposed that the total community of fish species of shelf environments be conceived as metapopulation aggregates of both estuarine and non-estuarine populations. As estuarine-dependent populations are a large portion of the total, it is probable that environmental alterations occurring in estuaries may have major influences on shelf biodiversity and ecosystem dynamics. The conclusion is that further understanding coastal-zone-ecosystem dynamics will depend on the fusion of metapopulation studies and the concepts of landscape ecology.