Comparative ecology of nekton residing in a tidal creek and adjacent seagrass meadow, community composition and structure

Abstract

A structural analysis of the nekton communities occupying a tldal creek and adjacent seagrass meadow at Vaucluse Shores, Virginia (Delmawa Peninsula, USA) is presented along with a comparison of the relative value of each habit to the early life stages of marine and estuarine species. Seagrass meadows were characterized by significantly greater richness and diversity of constituent taxa; both areas, nevertheless, contained mixtures of habitat specialists and wide-ranging (ubiquitous) species that displayed no area1 preferences. Except for a few resident forms, much of the nekton community in the grassbed was comprised of less abundant 'southern' species that entered the Chesapeake Bay in late summer and fall. Reciprocal averaging and numerical classification procedures applied to pooled station collections further indicated the clinal nature of species distributions among habitats, but also clearly demonstrated several microhabitat associations for either the Zostera marina or Ruppia maritima portions of the grassbed. The sciaenid. Leiostomus xanthurus dominated the nekton in both habitats, with > 80 % of all individuals but were nearly 4 times as abundant in the tidal creek. Abundance distribution and length frequency analyses for this species indicated that the marsh is the preferred habitat but also that larger individuals in the population continuously 'bled off' into downstream areas. Two other species of regional importance. Callinectes sapidus and Paralichthys dentatus, also utilized both habitats extensively. Late in summer and early fall, juveniles of both species were more abundant in the grassbed, whereas earlier in the year, they were randomly dispersed. The apparently limited dependence on both the grassbed and tidal creek by the young of local taxa is strikingly different when compared to similar habitats at lower latitudes. In light of the differences established between these habitats and their utilization by different species, an attempt is made to identify potentially important determinants of community structure and relate these to the success of individual populations in both areas. Because few expenmental data are available, our presentation, by necessity, is hypothetical.