Eutrophication of sediments in the Cullera bay: composition and abundance of macrobenthos

Abstract

Nutrient retention in estuaries and semi-enclosed bays is a principal contributing factor to the relatively high production of these marine systems. Cullera bay occasionally presents serious environmental problems owing to discharge of the Jucar freshwater, sewage from a marine outfall and nutrients release of the sediment. This study examine the macrobenthos in order to evaluate their composition and abundance in anthropogenically impacted coastal sediments and waters. A total of five field campaigns were carried out during years 2002-2003, but, in this paper, we shown the results of the first campaign. The macrobenthos was collected at twelve stations along three transects using a type of Peterson grab, but only we have used the bivalve molluscs because they represent most benthic biomass. To evaluate the influence of environmental factors on the bivalves, we took undisturbed sediment and bottom-water samples at fourteen stations. In water samples we have studied salinity, nutrients, chlorophyll a and suspended solids, and granulometry, organic matter, total nitrogen and total phosphorous in sediment samples. In general exists a high organic matter accumulated in sediments of the bay that increases with depth. The concentration of nutrients of the waters are low, however, the concentration of chlorophyll a suggests a eutrophic character of the shallowest zones. Although bivalve density do not show a clear pattern with every parameters measured, we find some relationships between most abundant bivalves (Donax spp. and Spisula subtruncata) and depth, chlorophyll a of waters and granulometry and nutrients of sediments.