Changes in the benthic macroinvertebrate fauna of a large microtidal estuary following extreme modifications aimed at reducing eutrophication

An artificial channel was opened in 1994 between the microtidal Peel-Harvey Estuary and the Indian Ocean to increase tidal exchange and thus ameliorate the problems of eutrophication. Although this greatly reduced macroalgal and cyanobacterial growths and the amount of particulate organic matter, our data indicate that, contrary to managerial expectations, the benthic environment has deteriorated. Thus, although macroinvertebrate density has declined as predicted, taxonomic distinctness (Δ*) has also declined and species composition has become more variable. Macroinvertebrate composition has also changed markedly at the species, family and even phylum levels. The Crustacea, the most sensitive of the major macrobenthic taxa to environmental stress, has become proportionally less abundant and speciose, whereas the Polychaeta, the least sensitive, was unique in showing the reverse trend. The benthos of the Peel-Harvey Estuary is thus apparently more stressed than previously, probably due to the multiple effects of a great increase in system use

Benthic macroinvertebrates as indicators of environmental deterioration in a large microtidal estuary

This study tested the hypothesis that, during recent years, the benthic macroinvertebrate fauna of the large basin of the Swan-Canning Estuary has changed in ways consistent with deteriorating environmental conditions in that estuary. Between 1986/7 and 2003/4, the compositions of that fauna altered markedly at the species and even family levels. Thus, the densities and number of species of molluscs, and especially of crustaceans, which are particularly susceptible to environmental stress, declined, while those of the more tolerant polychaetes increased. However, taxonomic distinctness declined consistently only at one of the four widely-spaced sampling sites and the dispersion of samples did not differ markedly between periods, indicating that the benthic fauna has not undergone such extreme changes as in the nearby Peel-Harvey Estuary. It is thus proposed that benthic macroinvertebrates can act as important indicators of the severity of environmental degradation in microtidal estuaries in regions where such perturbations are increasing