Long-term comparison of algal assemblages dominated by Cystoseira crinita (Fucales, Heterokontophyta) from Cap Corse (Corsica, North Western Mediterranean)

Abstract

Species composition and abundance of present rocky shore assemblages at Cap Corse (Corsica, North Western Mediterranean) dominated by the fucalean alga Cystoseira crinita are compared with similar data obtained almost 50 years ago. Fifteen sites at five different localities where dense C. crinita assemblages were present in the past were revisited in June 2007. Possible differences between the two sampling times were investigated, applying various multivariate analysis techniques available in the statistical package PRIMER v.6. Dense assemblages dominated by C. crinita were found at 14 out of the 15 surveyed sites, showing a similar structure and composition to the assemblages studied in the past. PERMANOVA indicated slight differences in species composition and abundances between old and new surveys. These differences can be summarized as a higher abundance of encrusting species (up to 3 times greater cover), and more sciaphilic turf-forming species (3 to 60-fold greater, depending on the species) and Cladophora spp. (20 times greater) in the present study than in the old study. Furthermore, the present assemblages showed a lower abundance of photophilic turf-forming species. These differences could be due to different taxonomic competence between observers, seasonal fluctuations or long-term changes. Assemblages dominated by Cystoseira crinita in Cap Corse were confirmed to be common, as they were found and sampled at 22 new sites around the island.