Community metabolism in temperate maerl beds. Ⅰ. Carbon and carbonate fluxes

摘要

Maerl community respiration, photosynthesis and calcification were measured seasonally in the Bay of Brest (France). The dynamics of oxygen, carbon and carbonate fluxes at the water-sediment interface were assessed using benthic chambers. Community respiration (CR) fluctuated in accordance with the seasonal changes in water temperature, from 1.5 mmol C m~(-2) h~(-1) in winter to 8.7 mmol C m~(-2) h~(-1) in summer. Mean gross community production (GCP) varied significantly among seasons, according to incident irradiance and temperature, from 3.4 mmol C m~(-2) h~(-1) in winter to 12.7 mmol C m~(-2) h~(-1) in summer. Mean annual P_(max) for the P-E curve was estimated to 13.3 mmol C m~(-2) h~(-1). Carbonate precipitation only occurred during light incubations and varied seasonally from 0.7 mmol CaCO_3 m~(-2) h~(-1) in winter to 4.2 mmol CaCO_3 m~(-2) h~(-1) in summer. Mean annual P_(max) was 3.2 mmol CaCO_3 m~(-2) h~(-1). Annual CR was estimated to 407.4 g C m~(-2) yr~(-1), and GCP, to 240.9 g C m~(-2) yr~(-1). Maerl communities are, therefore, heterotrophic systems (GCP:CR = 0.6), and are a source of CO_2 for surrounding environments. In addition, CO_2 released by calcification averaged 39.2 g C m~(-2) yr~(-1). Maerl community annual carbonate production was estimated to 486.7 g CaCO_3 m~(-2) yr~(-1); they are therefore one of the most important carbonate producers in shallow coastal waters.