Interpreting Temporal Disturbances in an Estuarine Benthic Community under Combined Anthropogenic and Climatic Effects

Abstract

The structure of the subtidal macrobenthos communities in the Palmones River estuary (Algeciras Bay), Southern Spain, was studied from 1992 to 1997 along a gradient running from an internal area of the estuary (three stations) to the exterior (one station). The composition of the macrofauna was studied at each of these stations, and the granulometry and organic content of the sediment were analysed. By means of univariate and multivariate analyses we have been able to identify significant changes in the stations throughout the period of research. The data on the structure of the communities reveals import ant changes of species and other population parameters such as abundance, diversity and evenness from one year to the next particularly at the station located at the mouth of the rivers mouth,  possibly provoked by three synergetic effects : sewage which is mainly organic (of anthropogenic origins), the river's diminished renewal capacity due to the progressive closure at its mouth from accumulated sediment and the  heavy rainfalls during 1996 and 1997 which have recently restored the river's renewal capacity, and have added to the increase water discharge from the "Charco Redondo" dam situated upstream. The physico-chemical analyses which were carried out also support these conclusions.