Relationships between algae, benthic herbivorous invertebrates and fishes in rocky sublittoral communities of a temperate sea (Mediterranean)

In situ surveys were used to examine the contribution of benthic herbivorou s invertebrates and fishes to the organization of Mediterranean rocky subli ttoral communities. Shallow (1-3 m) and deep (6-8 m) sampling sites, in nat ural areas and on man-made structures, were characterized by a structural c omplexity index (cavity index and mean size of cavity aperture), algal cove r (encrusting, turfy, shrubby and arborescent algae) and the density of ben thic herbivorous invertebrates and fish. A relationship between structural complexity and biota was only evident for some fish species (Diplodus spp. and Sarpa salpa) at deep sites, where they not only feed but also shelter. Three benthic herbivorous invertebrates, the sea urchins Paracentrotus livi dus and Arbacia lixula, and the limpet Patella caerulea, are associated wit h communities dominated by encrusting algae. Variations in their abundance and role in structuring algal communities follow a depth gradient: P. caeru lea and A. lixula are mainly present at shallow sites and P. lividus at dee p sites. These benthic herbivorous invertebrates may account for the struct ure of shallow algal communities. In contrast, at deep sites, fishes (the o mnivorous Diplodus spp. and the herbivorous S. salpa) have a potential impo rtance in controlling sublittoral algae, in addition to invertebrates. It i s suggested that the ecological impact of herbivorous and omnivorous fishes in temperate seas could be greater than is generally thought. Experiments should be designed to validate this postulate. (C) 2000 Academic Press.