Exploring the relationships between abiotic variables and benthic community structure in a polluted estuarine system

Assessed was the effect of a man-induced interference in an estuarine system by monitoring a set of hydrographic and sedimentary variables together with a faunal survey of intertidal mudflats. A reference site was established in a nearby unpolluted estuary. A principal components analysis (PCA) reduced the original environmental data to a few more manageable factors. PCA factor I, defined by changes in salinity at the surface of the water column and dissolved oxygen at the bottom, explained 40% of the total variance. Pair-wise correlations between different structural metrics and PCA factor I explained up to 70% of the variability observed in the community metrics. Macrobenthic communities were simpler (with minor values of abundance, diversity, evenness and a much lower value of biomass) where dissolved oxygen at the bottom of the water column was minimum. An afaunal stage developed along intertidal mudflats where anoxic conditions prevailed. There was a large “weight-of-evidence” that a depletion of dissolved oxygen was causing a severe stress to the estuarine biota.