CALCIUM-CARBONATE PRODUCTION OF A DENSE POPULATION OF THE BRITTLE STAR OPHIOTHRIX FRAGILIS (ECHINODERMATA, OPHIUROIDEA) - ROLE IN THE CARBON-CYCLE OF A TEMPERATE COASTAL ECOSYSTEM

The production of calcium carbonate by a dense Ophiothrix fragilis pop ulation was calculated in order to investigate its role in the carbon budget of a temperate coastal ecosystem (Dover Strait, eastern English Channel). Production, calculated using monthly data of population den sity, demographic structure and a size/CaCO3 conversion, was 682 g CaC O3 m(-2) yr(-1). Assuming that the molar ratio of CO2 released to CaCO 3 precipitated varied with temperature between 0.66 and 0.73, this pro duction would result in the release of 4.8 mol CO2 m(-2) yr(-1). This calculation reinforces the suggestion that this coastal system is a so urce of CO2 to the atmosphere.