Changes in the species composition and structure of Mediterranean macroalgal-dominated communities from the upper sublittoral zone are described along a gradient of nutrient enrichment coming from a urban sewage outfall. Ulva-dominated communities only appear close to the sewage outfall. Corallina-dominated communities replace ulvacean algae at intermediate levels of nutrient enrichment. Cystoseira-dominated communities thrive in the reference site but already appear at nutrient levels that are threefold higher than those reported from unpolluted sites. Assemblage variability of Cystoseira-dominated communities decreases along the gradient of nutrient enrichment. Methods based on the functional-form groups of macroalgae to assess the water quality provide equivocal results at intermediate levels of nutrient enrichment because species belonging to the same group can display a completely different response to pollution. Alternatively, methods based on indicator species showed correlated evidence among species abundances and pollution levels and seem to have better performances in water quality assessment.
Within the frame of a wider research project on the littoral ecosystem of the Bay of Blanes (NW Mediterranean), the dynamics of shallow soft-bottom macroinfaunal assemblages of medium-to-fine-sand sediment communities of Spisula subtruncata have been followed since March 1992. These assemblages exhibited a very predictive annual cycle. Abundance and biomass rose sharply during spring, followed by a striking drop through summer showing lower values during autumn and winter. These cycles were consistent with the temporal variation of key macroinfaunal species in these shallow habitats: Spisula subtruncata, Owenia fusiformis, Ditrupa arietina, Lucinella divaricata, Echinocardium mediterraneum, Spio decoratus, Chone infundibuliformis, Paradoneis armata, Mediomastus fragilis, Protodorvillea kefersteini, Branchiostoma lanceolatum, Glycera cf. capitata and Callista chione. These species were included in ecological groups based on the trends observed during the 4 years of seasonal dynamics which are presented.
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