Interpreting temporal disturbances in an estuarine benthic community undercombined anthropogenic and climatic effects

The structure of the subtidal macrobenthos communities in the Palmones Rive r estuary (Algeciras Bay, Southern Spain), was studied from 1992 to 1997 al ong a gradient running from an internal area of the estuary (three stations ) to the exterior (one station). The composition of the macrofauna was stud ied at each of these stations, and the granulometry and organic content of the sediment were analysed. By means of univariate and multivariate analyse s we have been able to identify significant changes in the stations through out the period of research. The data on the structure of the communities re veals important 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 origin), the river's diminished renewal capacity due to the progressive cl osure at its mouth from accumulated sediment, and the heavy rainfalls durin g 1996 and 1997 which have recently restored the river's renewal capacity, and have added to the increase water discharge from the "Charco Redondo" da m situated upstream. The physico-chemical analyses which were carried out a lso support these conclusions.