Primary production of benthic microalgae in an intertidal sand flat of the Ria de Arosa, NW Spain

Primary production of benthic microalgae was studied in an intertidal sand flat in the Ria de Arosa (NW Spain), where a n intensive bivalve aquaculture takes place. Active and degraded pigments, organic matter, and vertical migration of algae were also studied. Total annual production. combining high and low tide values, reached 79 g C m-2, while water column production in the same place was only 6 gC m-2, which suggests that resuspended benthic microalgae can be a major food source for bivalves. Year-round production showed no clear seasonal peaks, probably due to intense sediment d~sturbance by culturing manipulations, and to high detrital supply: 94 to 98 % of organic matter in the sediment is allochtonous non-living material.