Spatial variations of phytoplankton community structure in a highly eutrophicated coast of the Western Mediterranean Sea

Abstract

Pinedo is a small beach placed at the southern side of Valencia (Eastern Spain). This coastal area has became highly eutrophicated because of the discharge of a large flow of urban wastewaters at the shore line. In order to assess the environmental impact of a new sea outfall and to study the pbytoplankton and nutrients dynamics of this eutrophicated system a broad survey was conducted between May 1989 and April 1990. Physical and chemical parameters were measured through a transect laying between the wastewater discharge point and the open sea. In this paper we report preliminary results about the variations observed in the pbytoplankton community along this sharp environmental gradient Three main zones with particular pnytoplankton structure appear well differentiated. The first is an inshore zone very influenced by continental loadings where brackish and polluted waters were found. Pbytoplankton shows relatively low numbers being dominated by Chlorophyceae and a few other eurihaline species. An intermediate zone has salinities close to sea water but nutrient concentrations are high enough to allow maximum development of pbytoplankton, which reaches its highest abundance and diversity values. Diatoms, dinoflagellates and some flagellates (Prymnesiophyceae and Cryptophyceae) dominate the eukaryotic community of this zone. Gradual impoverishment of sea water is accompanied by a rapid decrease of pbytoplankton biomass, which is reduced to scarce flagellates populations at the open sea stations.