Diversity of benthic macrofauna of the flood-tidal delta of the Nahoon Estuary and adjacent beach, South Africa

Abstract

Macrobenthos of the Nahoon estuarine flood-tidal delta was surveyed to determine species composition, distribution and abundance; establish possible patterns in community structure and compare assemblages with those of adjacent sandy beach and lower estuary. Macrozoobenthos retained by a 1 mmmesh was collected by  sampling four 1m² replicates, at 14 sites in the flood-tidal delta using a suction-sampler and at three sites on the beach by digging quadrats. A total of 118 species was identified: 106 in the flood-tidal delta and 36 on the beach. Major taxa were: Crustacea 60 species, Mollusca 20, Polychaeta 27, Insecta 6, Pisces 3.  Maximumdensity was 5171m² (Urothoe serrulidactylus). Species richness  decreased from beach to river mouth and increased from mouth sites to sites  furthest from the mouth. In all areas, species richness increased from high shore to low shore. Multivariate analyses of species abundances identified four groups of sites, showing a gradual change in community structure from the beach into the estuary. Species analyses identified indicator species of these groups. The flood-tidal delta had a characteristic set of species, some of which were largely restricted to this area, while others occurred more abundantly on the beach or in the estuary. Several typical sandy beach species were more abundant in the flood-tidal delta than on the beach. Sites furthest from the mouth were characterized by  estuarine species.

Key words: macrobenthos, open estuary, beach, intertidal ecology.