Spatial and temporal changes in beach meiofaunal communities of the Ligurian Sea (NW Mediterranean)

Abundance and community structure of the intertidal meiofauna were studied in five beaches of the Ligurian Sea (northwestern Mediterranean) in Summer 1994 and Winter 1995 and related to the main environmental variables such as temperature, food availability, hydrodynamic stress and grain size of the sediment. Mean meiofaunal density ranged from 130.7 ± 212.5 ind/10 cm² in winter to 230.8 ± 336.6 ind/10 cm² in summer. Water temperature, wave action and sediment texture appeared to be the main factors affecting meiofaunal communities, while organic matter content appeared to play a minor role, although highest densities were reported from beaches close to the Entella River estuary characterized by large amounts of organic detritus. Meiofaunal community structure in sheltered beaches was characterized by the dominance of nematodes and turbellarians, whereas high-energy beaches showed the dominance of harpacticoid copepods. Meiofaunal density and number of taxa increased with increasing sediment sorting. Meiofaunal community structure displayed clear changes between summer and winter: nematodes were generally the dominant taxon in winter (on average 77.3% of the total meiofaunal density) whilst copepods generally dominated in summer (on average 62.5% of the total meiofaunal density). The results of this study suggest that different parameters might have different roles in meiofaunal characteristics: 1) the very low absolute meiofaunal densities are consistent with the low sedimentary OM content; 2) changes in meiofaunal densities appear characterized by a clear seasonality (related to temperature); and 3) grain size and/or exposure degree might have a preeminent role in affecting community composition and aggregation.