Community structure and intertidal zonation of the macrobenthos on a macrotidal, ultra-dissipative sandy beach: Summer-winter comparison

Community structure and intertidal zonation of the macrobenthos on a macrot idal, ultra-dissipative beach were studied. On the beach of De Panne, Belgi um, six transects perpendicular to the waterline teach with five stations) were sampled in September 1995 (summer) and March 1996 (winter). The 30 sta tions were distributed across the continuum from mean high water spring to mean low water spring in order to sample the macrobenthos at different leve ls of elevation. The 39 species found had total densities up to 5,500 ind m (-2) in summer and 1,400 ind m(-2) in winter. The highest densities were fo und in the spionid polychaetes Scolelepis squamata and Spio filicornis, the nephtyid polychaete Nephtys cirrosa, the cirolanid isopod Eurydice pulchra , and the haustorid amphipods Bathyporeia spp. Based on species composition , specific densities, and biomass, two species associations were defined: a relatively species-poor, high intertidal species association, dominated by S. squamata and with an average density of 1,413 ind m(-2) and biomass of 808 mg AFDW m(-2) (summer); and a relatively species-rich, low intertidal s pecies association, dominated by N. cirrosa, and with an average density of 104 ind m(-2) and biomass of 162 mg AFDW m(-2) in summer. For both seasons , the high intertidal species association was restricted in its intertidal distribution between the mean tidal and the mean high-water spring level, w hereas the low intertidal species association was found from the mean tidal level to the subtidal. The latter showed good affinities with the subtidal N. cirrosa species association, occurring just offshore of De Panne beach, confirming the existence of a relationship between the low intertidal and subtidal macrobenthic species associations. Summer-winter comparison reveal ed a strong decrease in densities and biomass in the high intertidal zone d uring winter. Habitat continuity of the low intertidal zone with the subtid al allows subtidal organisms to repopulate the low intertidal zone.