Marine and brackish-water ostracods as sentinels of anthropogenic impacts

This review analyses the ostracod responses to pollution-induced environmental changes by anthropogenic impacts. Different biological features such as the variability of the local assemblages, population density, species diversity, age population structure and polymorphism, coupled with the favourable results of recently developed bioassays, suggest that these microorganisms may be included between the most promising sentinel groups in both brackish and marine areas. In meiofaunal studies, these microcrustaceans show high sensitivity to heavy-metal pollution, oil discharges and anoxic conditions. In specific investigations based on surveys of recent populations or stratigraphic box-core analysis, both ostracod densities and species diversities decrease remarkably near sources of pollution after a period of pollutant discharge, with a lesser impact in distant or protected areas. Strong heavy metal pollution or frequent oil spills may cause the disappearance of these organisms or a strong reduction in the number of individuals in a relatively short time period, whereas total or partially untreated urban wastes or agricultural discharges causing eutrophication effects lead to the dominance of distinctive species that are adapted to hypoxic conditions. vironmental improvement derived from the recent implementation of legal regulations in some countries has also been documented in the changes in ostracod assemblages back to pre-disturbed conditions. In addition to population and community changes, morphological and geochemical changes can also be detected in the ostracod carapace, which serves as a tracer of the water quality during the moulting processes.