Benthic Mollusk Biodiversity Correlates with Polluted Sediment Conditions in a Shallow Subtropical Estuary

To quantify the ecological impacts of organic sediments and environmental dredging, benthic mollusks were chosen as bioindicators of environmental change, measured as sediment organic content and associated parameters. Data on species richness, ecological diversity (which was measured as biodiversity), and abundances were collected alongside sediment and near-bottom water quality data before, during, and after environmental dredging. Organic sediment content was found to have an inverse logarithmic relationship with benthic mollusk biodiversity, species richness, and abundance. Post hoc analyses found that percent dissolved oxygen, which correlates with sediment organic content, was responsible for 29.31–34.12% of the benthic mollusk community variation. Sediments with lower organic content had higher biodiversity (organism densities up to 1 organism m−2), abundance (over 2.0 × 105 organisms m−2), and species richness (organism densities up to 4 organisms m−2). In comparison, sediments with higher organic content had low biodiversity (organism densities 0–1 organisms m−2), abundance (as low as 0 organisms m−2), and species richness (organism densities as low as 0 organisms m−2).