Benthic macrofauna communities reflect eutrophic condition in a low-inflow estuary

Nutrient enrichment drives potentially severe changes in low-inflow and temporarily closed estuaries where tidal mixing and freshwater flushing is limited, and bottom-water anoxia occurs frequently. Our research assesses the influence of nutrient enrichment by comparing macrobenthos community metrics in a persistently hypereutrophic South African estuary. This is then compared to published literature for an estuary with a similar catchment size and mean annual runoff, but which experiences limited anthropogenic nutrient input. Macroinvertebrate abundance and richness were higher in an estuary with limited anthropogenic nutrient loading, and this varied seasonally for both estuaries. Oxygen saturation had a significant influence on taxonomic level abundances, with lower oxygen levels in the polluted estuary reducing macroinvertebrate abundances. Macroinvertebrates tolerant of organic pollution (e.g., Oligochaeta) were also more abundant in the polluted estuary. This study highlights the effects of increased nutrient loading in low-inflow estuaries and confirms the supposition from several previous studies that macrozoobenthos could be used as a responsive tool from a bioindicator perspective to monitor eutrophication.