Seaward Change and Zonation of the Sandy-Shore Macrofauna at Perdido Key, Florida, U.S.A.

Abstract

To elucidate spatial community patterns, we sampled macrofauna from 36 stations located along four 800 m seaward transects at Perdido Key, Florida. Several faunal indices, including species richness, total density, diversity, and species composition, changed markedly with increasing distance from shore. Species richness was greater at the outer stations by a factor of 20, ranging from five species per 0·125 m 2 in the swash zone, to as many as 100 species per 0·125 m 2 at 800 m offshore. Total density also increased seaward from shore by an order of magnitude, from 2000 per m 2 to 20 000 per m 2. Seaward spatial distributions of dominant species along the four transects exemplified coenoclines with distinct breaks, noticeable as steep reductions in densities of contiguous dominant species. Coenocline breaks coincided with peak diversity and evenness levels as well as with relatively low total densities at distances between 100 and 200 m from shore, midway along the seaward slopes of transect depth profiles. These faunal discontinuities presumably coincided with intermediate levels of disturbance from wave action. Nearshore spatial changes in faunal indices among transects corresponded with changes in habitat, as characterized by depth and sediment. The existence of four major faunal zones within the 800 m seaward distance was suggested by a Detrended Correspondence Analysis of 45 common species and 36 stations. Taken together, these findings indicated that a primary environmental gradient consisting of seaward variation in depth, sediment characteristics, and turbulence largely determines sandy-shore community structure.