Shallow rocky bottom benthic assemblages as calcium carbonate producers in the Alboran Sea (southwestern Mediterranean)

Zonation patterns and species composition of the different assemblages encountered along the bathymetric axis are considered in order to quantify the biomass and calcium carbonate content of communities thriving in rocky bottoms of La Herradura (southwestern Mediterranean) between 0 and 50 m depth. Algal biomass is lower but total biomass is slightly higher to values recorded in other Mediterranean areas due to the high biomass of suspension feeders. Since most of the animals and algae with high biomass have calcareous skeletons, the calcimass is rather high (1 100 to 2400 g . CaCO3.m(-2)) when compared to other temperate and Mediterranean sites. A tentative estimate of yearly carbonate production yields 1 000 g . CaCO3.m(-2).y(-1) for the rocky bottoms of the infralittoral zone and 680 g . CaCO3.m(-2).y(-1) for the circalittoral zone. This relatively high carbonate production may be related to the particular hydrographic processes which take place in this area (mixing of Mediterranean and Atlantic waters, upwelling of Mediterranean deep waters). (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.