Affinities of some common estuarine macroinvertebrates to salinity and sediment type: Empirical data from Eastern Cape estuaries, South Africa

Abstract

Fourteen species of subtidal macrobenthos present in thirteen Eastern Cape  estuaries, South Africa, were compared with regard to correlations with two  important environmental variables (salinity and sediment mud content). Species were divided into five different faunal components based on their affinity with one of the two variables, namely marine species, oligohaline species, estuarine sand species, estuarine mud species, and species whose distribution seemed independent of either environmental variable. Although most species exhibited wide tolerance ranges to both environmental variables, preference ranges could be identified in many cases. Among the fourteen species studied, three were found mostly at high salinities, two were confined to sandy substratum, and four showed a clear preference for muddy sediment. The crab  Paratylodiplax algoense was identified as a euryhaline marine species and the larvae of chironomid midges, previously believed to be oligohaline species, were found to be tolerant to near seawater salinities.

Key words: subtidal macrobenthos, true estuarine species, estuary, salinity,  substratum.