Short-term Persistence and Stability of Barrier Island Fish Assemblages

The semi-permanent pools along the south shore of a Gulf of Mexico barrier island provide a natural setting in which to investigate short-term faunal stability and persistence. All pools were located south of the primary dune line and may be formed when sand bars join with the beach, or when storms fill depressions. The pools offer a physiologically harsh environment, but overall support a fish fauna of 39 species which is dominated numerically by Cyprinodon variegatus, Gambusia holbrooki and Poecilia latipinna. Persistence of the overall fish assemblage was only moderate (0•61) and seasonal stability of the pool assemblages was variable, with five assemblages showing concordance and four non-concordance. Pools with stable assemblages could not be differentiated from those with non-stable assemblages on the basis of physicochemical characteristics. However, pools with greater faunal stability were those colonized by marsh inhabiting species, while pools dominated by colonizers from the nearby surf zone tended to be more variable. Many surf zone species apparently cannot tolerate the physiological demands of the pools and soon go locally extinct. Thus, assemblage stability is largely determined by the vagaries of colonization and the relative age at which a pool is sampled.