Spatio‐Temporal Distribution of Algal and Animal Communities in a Posidonia oceanica Meadow

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Abstract
Investigations were carried out in a Posidonia oceanica meadow at Ischia (Gulf of Naples) along a depth gradient from 1 to 32 m in November 1979 and May 1981.In these two months, different discontinuities were found at the sampling stations (1, 5, 10, 20, 30 m) at 10 m for leaf features, between 1 and 5 m for the algal community and the vagile fauna. The leaf features (length, surface, and biomass) along the transects show a delay in leaf production toward the deeper stations, below the thermocline.The algal community shows in both seasons and in all stations a persistence of an encrusting layer, mostly represented by Corallinaceae and the brown alga Myrionema orbiculare, while at the shallowest station (1 m) the community is characterized by a more developed upright layer.The vagile fauna of the leaf stratum, mostly represented by Polychaeta, Mollusca, and Crustacea (Peracarida and Decapoda), shows a consistent zonation in both seasons along the transect. A superficial community at I m, characterized by a low number of species and individuals and specialized for high environmental energy levels, and a deeper community, persistent in time and more strictly related to the Posidonia oceanica meadows, are identified.The influence of environmental factors and the importance of meadow structure for the zonation of the algal and animal communities are discussed.