Biodiversity and biogeographical patterns of molluscan assemblages in vegetated and unvegetated habitats in the northern Alboran Sea (W Mediterranean Sea)

This paper evaluates the influence of habitat heterogeneity, inter-habitat connectivity, and biogeograhical patterns in the context of a biodiversity hotspot in an Atlantic-Mediterranean marine transition area. We analyzed some biological and ecological aspects of molluscan assemblages inhabiting different habitats located in the northwestern Alboran Sea, in order to elucidate the inter-habitat connectivity among coastal habitats, and to understand the contribution of each habitat to the integrity of the infralittoral ecosystem. The assessment of molluscan assemblages was performed by combining information regarding (1) feeding guilds, to analyze trophic strategies; (2) microhabitat preference, to study the link between habitat heterogeneity with biodiversity; and (3) biogeographical affinities, to identify distributional patterns of molluscs. A total of 354 molluscs were identified, with vegetated habitats harbouring the highest number of species. A wide variety of trophic strategies were observed, with infaunal filter feeders, specialized carnivores living on sessile invertebrates and microalgal grazers dominating the assemblages. Most of the species have a wide distribution while few strictly Mediterranean species have been collected. The presence of subtropical species highlights the uniqueness of this area in European seas. The high β-diversity value obtained is indicative of high habitat heterogeneity and a high amount of uncommon species, some of them displaying their sole European populations. The different assemblages enrich the global taxocoenosis through complementarity, with an important inter-habitat connectivity reflected by the different temporal ordination of samples according to both micro-habitat affinities and feeding guilds. This work highlights the balanced contribution of soft and vegetated bottoms as reservoirs of biodiversity.