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 population 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 density, demographic structure and a size/CaCO3 conversion, was 682 g CaCO3 m(-2) yr(-1). Assuming that the molar ratio of CO2 released to CaCO3 precipitated varied with temperature between 0.66 and 0.73, this production 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 source of CO2 to the atmosphere

A closed-chamber CO2-flux method for estimating intertidal primary production and respiration under emersed conditions

This paper describes a closed-chamber method for measuring CO2 fluxes in intertidal soft sediments during periods of emersion. The method relies on closed-circuit incubations of undisturbed sediment and measurement of CO2 exchanges using an infrared gas analyser. The method was assessed during field experiments, both in light and dark conditions, on an exposed sandy beach and in an estuary. The rates of gross community production measured under moderate diance (4.2 mg C m(-2) h(-1) on the exposed sandy beach and 35 mg C m(-2) h(-1) in the estuary) are in good agreement with rates reported in the literature. In conjunction with appropriate sampling strategies, this method can be useful for estimating and comparing production of intertidal areas or for assessing factors that influence production