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 Pmax 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 CaCO3 m-2 h-1 in winter to 4.2 mmol CaCO3 m-2 h-1 in summer. Mean annual Pmax was 3.2 mmol CaCO3 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 CO2 for surrounding environments. In addition, CO2 released by calcification averaged 39.2 g C m-2 yr-1. Maerl community annual carbonate production was estimated to 486.7 g CaCO3 m-2 yr-1; they are therefore one of the most important carbonate producers in shallow coastal waters.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Lavigne and Gattuso, 2011) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI).

Supplement to: Martin, Sophie; Clavier, Jacques; Chauvaud, Laurent; Thouzeau, Gérard (2007): Community metabolism in temperate maerl beds. I. Carbon and carbonate fluxes. Marine Ecology Progress Series, 335, 19-29