The sea urchin Diadema antillarum Phillipi, 1845 influences the diversity and composition of the mobile mega-invertebrate community on rocky bottoms off the Canary Archipelago

The effect of the sea urchin Diadema antillarum density over the diversity and composition of the mobile megainvertebrate community (\u3e 2 cm) inhabiting shallow rocky reefs off the Canary Archipelago (eastern Atlantic) is described. Specifically, it was predicted that (1) high densities of D. antillarum produce a low diversity of the mobile megainvertebrate community, and (2) the composition of this community changes between rocky bottoms (= reefs) under different densities of D. antillarum. The presence of megainvertebrate taxa, and the density of D. antillarum individuals were recorded visually using 2 x 2 m quadrats (n = 16 replicates) in each of 24 locations (three locations in each of the eight main islands of the archipelago), which were visited in four occasions between February-2003 and October-2004. Thritythree taxa of mobile mega-invertebrates were observed. We registered a decline in the richness of such assemblages with increasing densities of D. antillarum (rs = -0.20; PD. antillarum (\u3c 2 ind. m-2). However, species richness was always low (\u3c 9 species) in those locations with high densities of D. antillarum (\u3e 8 ind. m-2). A CAP ordination analysis showed significant differences in the composition of the mega-invertebrate community between rocky bottoms under different densities of D. antillarum, and we registered a negative correlation between the presence of some taxa and the densities of sea urchin. Consequently, the sea urchin D. antillarum influences the diversity and composition of the mobile mega-invertebrate community on rocky bottoms off the Canary Archipelago