Comparison of the epifauna spatial distribution in Posidonia oceanica, Cymodocea nodosa and unvegetated bottoms: Importance of meadow edges

In order to detect the influence of seagrass, the most important habitats o f shallow soft-bottom along the Mediterranean coast, on spatial distributio n of epifauna, four different types of habitat were sampled: Posidonia ocea nica, Cymodocea nodosa, edge of Posidonia meadow and sandy bottoms. Samplin g was carried out, using the hand net method, in Various random sites and a t different times (April 95, August 95 and February 96) on the Alicante coa st (SE Spain). A double taxonomic approach was used in order to detect spat ial and temporal changes in the abundance of the main taxonomic groups and amphipod species. The differences among habitats were detected by non-param etric multidimensional scaling (MDS) for community structure and by analysi s of variance for groups and amphipod populations. The community structure defined by the abundance of taxonomic groups was not significantly modified by the habitats. Single abundance of taxonomic groups also had no signific ant preference for the type of habitat except in the case of Acari, a group linked to Posidonia. However, certain trends of preference, such as mysids on Posidonia edge and isopods on Cymodocea, were detectable. On other hand , the amphipod assemblage showed important differences among habitats. Some species changed significantly in abundance depending on the habitat consid ered, e.g. Dexamine spiniventris and Perioculodes longimanus. It was possib le to conclude that there is an important influence of Posidonia and Cymodo cea on epifauna distribution by diversification of habitat structure on san dy bottoms, but it was more important at the species level than when consid ering taxonomic groups. Furthermore, sandy bottoms and the meadow edges had a relatively high importance on fauna distribution, depending on taxa and the period of the year. (C) 1999 Editions scientifiques et medicales Elsevi er SAS.