Phosphorus Forms Related to Sediment Grain Size and Geochemical Characteristics in French Coastal Areas

The composition and distribution of the macrobenthic community in a lagoon in the Po River delta was investigated by taking monthly samples at three sites during 1994. A total of 38 macroinvertebrate taxa, representing five phyla, were identified. Gastropods, amphipods, and chironomid larvae dominated the macrofauna in term of abundance, while in terms of biomass bivalves were the dominant taxon. Monthly total invertebrate abundance showed considerable fluctuations, depending on the season and on the presence of the red macroalgae Gracilaria verrucosa. In the central area of the lagoon, a significant relationship was demonstrated between macrobenthic community parameters and amount of macroalgal cover. Taking the most important species, i.e. those that contributed most to similarity within sites, only Cerastoderma glaucum was found to be negatively related to the amount of macroalgal biomass. Mean annual secondary production varied between 50 and 75 g AFDW m-2yr-1depending on the site, yielding P/B ratios between 1·02 and 1·08. Confinement and moderate disturbance due to the presence of algal cover are hypothesized to determine structure, composition, and production of the macrobenthic community in the Sacca di Goro.