Estuarine, Coastal and Shelf Science (1993) 36,81-104

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

C. F. Rakocinski, R. W. Heard, S. E. LeCroy,J. A. McLelland and T. Simons’Gulf Coast Research Laboratory and “Gulf Islands National Seashore,Otean Springs, MS 39564

Received 18 October 1991 and in revised form 4 May 1992

Keywords: sandy-shore macrofauna; coenocline; zonation; gradients

To elucidate spatial community pattems, we sampled macrofauna from 36stations located along four 800m seaward transects at Perdido Kep, Florida.Severa1 fauna1 indices, including species richness, total density, diversity, andspecies composition, changed markedly with increasing disrance from shore.Species richness was greater at the outer stations by a factor of 20, ranging fromfive species per 0.125 mZ in the swash zone, to as many as 100 species per 0.125 mZat 800 m offshore. Total density also increased seaward from shore by an order ofmagnitude, from 2000 per m2 to 20 000 per m’. Seaward spatial distributions ofdominant species along the four transects exemplified coenoclines with distinctbreaks, noticeable as steep reductions in densities of contiguous dominantspecies. Coenochne breaks coincided with peak diversity and evenness levels aswell as with relatively low total densities at distances between 100 and 200 mfrom shore, midway along the seaward slopes of transect depth profiles. Thesefauna1 discontinuities presumably coincided with intermediate levels of dis-turbance from wave action. Nearshore spatial changes in fauna1 indices amongtransects corresponded with changes in habitat, as characterized by depth andsediment. The existence of four majar fauna1 zones within the 800 m seawarddistance was suggested by a Detrended Correspondence Analysis of 45 commonspecies and 36 stations. Taken together, these findings indicated that a primaryenvironmental gradient consisting of seaward variation in depth, sedimentcharacteristics, and turbulence largely determines sandy-shore communitystructure.

Introduction

As coastal environments, exposed sandy-beach ecotones typically encompass steep sea-ward gradients in physical conditions. Seaward changes in intertidal and subtidal sandy-beach habitats can be characterized by complex gradients of interrelated environmentalfactors, including desiccation, wave action, currents, depth, sediment properties, andfood ( O l i v e r er al., 1980; Knott et al., 1983; McLachlan et al. , 1984; Fleischack &

Present address: Departrnent of Environmenral Science, Umversity of Virginia,Charlottesville VA 22903, U.S.A.

o272-7714~93~010081+24 SOS.OO/O 8 1993 Academic Press Limited