MEPS 335:31-41 (2007)  -  doi:10.3354/meps335031

ABSTRACT: Maerl community ammonium (NH₄⁺), nitrate + nitrite (NO₃^– + NO₂^–), dissolved silicic acid (DSi) and phosphate (PO₄^3–) fluxes were measured seasonally in the Bay of Brest (France). Nutrient exchanges at the sediment–water interface were assessed using benthic chambers. Nutrient fluxes differed between light and dark conditions, and fluctuated seasonally, with minimum values in winter and spring and maximum values in summer and autumn. In the dark, net community fluxes of NH₄⁺, NO₃^– + NO₂^–, DSi and PO₄^3– varied from 53 to 226 µmol N m^–2 h^–1, –107 to 70 µmol N m^–2 h^–1, 18 to 180 µmol Si m^–2 h^–1 and 5 to 19 µmol P m^–2 h^–1, respectively. In the light, NH₄⁺, NO₃^– + NO₂^–, DSi and PO₄^3– fluxes ranged from 17 to 110 µmol N m^–2 h^–1, –223 to –10 µmol N m^–2 h^–1, –34 to 112 µmol Si m^–2 h^–1 and 1 to 12 µmol P m^–2 h^–1, respectively. Temperature, community respiration, gross community production and bottom water dissolved oxygen and nutrient concentrations mainly controlled seasonal fluctuations of benthic nutrient fluxes. Annual net community fluxes of dissolved inorganic nitrogen (DIN), DSi and PO₄^3– were 6 g N m^–2 yr^–1, 10 g Si m^–2 yr^–1 and 2 g P m^–2 yr^–1, respectively. Annual gross community uptakes of DIN, DSi and PO₄^3– were 12 g N m^–2 yr^–1, 9 g Si m^–2 yr^–1 and 1 g P m^–2 yr^–1, respectively. Nutrient supply from the maerl community to the water column contributed potentially to between 18 and 55% of the annual phytoplanktonic production in the Bay of Brest.

KEY WORDS: Calcareous algae · Community metabolism · Nutrient fluxes · Nitrogen · Phosphorus · Silicon