The response of ostracod assemblages to recent pollution and sedimentary processes in the Huelva Estuary, SW Spain

By studying the ostracod assemblages in the Huelva Estuary, the impact of natural and human factors on the populations of these organisms can be determined. Three periods were defined in 12 cores collected along the estuary: (1) pre-industrial period (before 1966), with moderate pollution in some estuarine sectors because of prehistoric mining; (2) industrial period (1966–1985), with pollution increasing by wastes derived from industrial processes; and (3) post-industrial period (1991). No ostracods and live macrofauna were found in environments with extreme subaerial exposure (fluvial bars, meanders and salt marshes), even in pre-industrial sediments. During this period, the ostracod distribution was controled by the salinity tolerance in the main channel of the Odiel River, the euryhaline species being replaced by marine forms toward the estuary mouth. Acidic industrial wastes causes the disappearance of ostracod assemblages (mainly Loxoconcha elliptica) in this environment and the channel border. Fillings of some distributary channels have greatly affected the ostracod and macrofaunal assemblages in these zones, with a dramatic drop in the diversity and number of individuals. In April 1991, live ostracods were exclusively found in the Punta Umbría subsystem, a relatively protected environment because distance and salt-marsh barriers protect it from industrial effluents.