Classification and community structure of macrobenthos in the Hampton Roads area,Virginia

Benthic macrofauna was sampled by grab at 16 stations in Hampton Roads and the adjacent Elizabeth River, Virginia, USA. Samples were taken in February, May and August. Sampling sites and species were grouped by a classification strategy which basically consisted of the Canberra metric dissimilarity-measure and flexible and group average clustering. Following reallocations, 8 site groups and 16 species groups instructively classified the 47 sites and 93 species considered in the analysis. The sites were grouped into associations on mud, muddy-sand and sand-bottom, and those in the Elizabeth River. Species groupings distinguished a few species most frequent at Elizabeth River or mud and muddy-sand sites, larger numbers of species restricted to muddy-sand and sand or solely to sand sites, ubiquitous species, epifaunal species which were microhabitat-restricted, and seasonal species. An analysis of numerically dominant species in the different associations indicated the relative importance of ubiquitous species and seasonally abundant species. Community-structure statistics (species diversity, species richness and evenness) showed definite spatial and temporal patterns. Diversity was high at sand and muddy-sand sites and low at mud and Elizabeth River sites. This spatial pattern was predominantly one of species richness. At Elizabeth River and mud stations, diversity increased from February to August because of increased evenness, while at sand and muddy-sand stations, diversity peaked in May in response to both high species richness and high evenness. The applicability of community concepts, the causes of substrate specificity, seasonality and species diversity, and the effects of pollution on community structure are discussed.Contribution No. 553, Virginia Institute of Marine Science, Gloucester Point, Virginia, USA.