Twenty years of application of Polychaete/Amphipod ratios to assess diverse human pressures in estuarine and coastal marine environments: A review

Benthic indices based on the Polychaetes/Amphipods (P/A) ratio have been proposed to assess the environmental quality status of ecosystems in estuarine and coastal waters. Although the methods used to calculate these indices (essentially BOPA and BO2A) have been revised over the past two decades, the underlying approach corresponds to the contrasted responses of two benthic invertebrate groups to pollution, with polychaetes as tolerant/opportunistic species and amphipods as sensitive taxa. The Polychaetes/Amphipods ratio has been tested for monitoring major changes in benthic communities in response to a wide variety of different human pressures in estuarine and coastal environments (oil spills, urban sewage outfalls, enrichment in organic matter, etc.) and is used in 23 countries mainly in Europe, but also in Africa, Asia, Oceania and South America. This paper reviews the use of the P/A ratio (79 documents) in relation to a large panel of human activities, in transitional (estuaries and lagoons) and coastal waters. In some studies, BOPA and BO2A indices based on P/A ratios were selected in certain regions of Spain and Gibraltar to assess the quality of water bodies according to the Water Framework Directive. Moreover, most of these studies do not meet the necessary conditions for application of the indices. As a result, comparisons between P/A ratios and other benthic indices are inappropriate when assessing ecological quality status, which therefore reinforces the need to apply P/A ratios with precaution.