Macrobenthic communities in selected river-dominated estuaries in KwaZulu-Natal, South Africa : effects of contrasting environmental variables and seasonal flow changes.

Abstract

Globally, estuaries are ecologically important, but many are threatened by anthropogenic activities. Macrozoobenthos organisms are suitable ecological indicators in estuaries because they can detect the effects of stress and pollution. Spatial and temporal composition of macrozoobenthos communities were quantified and compared within and between the three estuaries (uMvoti, Thukela, and aMatikulu estuaries) in KwaZulu-Natal, South Africa, with different levels of human pressure in their catchments. Macrozoobenthos of each estuary was also related to its respective environmental variables. The aMatikulu estuary was selected as a reference site because of its relatively good ecological condition. Sampling dates represented low flow (August and September) and high flow (March and April) from 2014 to 2016. Macrozoobenthos abundance expressed as individuals per square meter (ind m 2 ) was highest in aMatikulu estuary (39,167 ind m 2 ), followed by Thukela estuary (29,299 ind m 2 ) and then uMvoti estuary (10,336 ind m 2 ). Within estuaries, number of taxa and abundance between years were significantly different (p , 0.05), and number of taxa and species diversity between estuaries were also significantly different (p , 0.05). Coarse and very coarse sand were the important environmental determinants in structuring the macrozoobenthos community in the uMvoti estuary, whereas turbidity and water temperature were the important determinants in structuring the macrozoobenthos community in the Thukela estuary. Very fine sand, mud, and salinity were among the most important environmental variables in structuring macrozoobenthos communities in the aMatikulu estuary. Environmental variables differed between estuaries; consequently, macrozoobenthos communities differed between these three systems. Outcomes of the present study indicated that macrozoobenthos communities respond to changes in environmental variables. Results of this study showed that different levels of human pressure in the catchments of these three estuaries could explain variation in their environmental variables. Such variation could increase differences in taxon composition and abundances between the three estuaries, although they are from the same geographical region with similar river-dominated functions.