THE ROLE OF MICROPHYTOBENTHIC PRIMARY PRODUCTION IN A MEDITERRANEAN MUSSEL CULTURE AREA

The production and biomass of microphytobenthos in a Mediterranean mus sel farm was studied during 1991-92. Gross and net microphytobenthic p roduction and respiration were calculated from oxygen fluxes in transp arent and black bell jars at two stations; sediments under a mussel ta ble and reference sediments, both located at 5 m depth. Net oxygen flu xes were mainly negative under the mussel tables (average -19.5 mg O-2 m(-2) h(-1), CV=132%), and microphytobenthos production could not mee t the sediment oxygen demand; in the reference sediments, microphytobe nthos production was responsible for net oxygen production (average +1 3.0 mg O-2 m(-2) h(-1), CV=118%). Benthic respiration rates were, on a verage, 47.3 mg O-2 m(-2) h(-1) (CV=82%) under the tables and 27.7 mg O-2 m(-2) h(-1) (CV=45%) in reference sediments. Aerobic respiration c ould mineralize less than 2% of the biodeposited carbon under the tabl es, implying that a large amount of organic material is accumulating u nder the tables, microphytobenthos was more productive than phytoplank ton in bottom waters. Per unit area, phytoplankton was more productive than microphytobenthos at both stations, especially in the area of th e mussel tables, where phytoplanktonic production was enhanced by the excretion products of mussels. Microphytobenthos was composed mainly o f diatoms in the sediments under the tables, while in reference sedime nts, the population was more diverse, with algae containing chlorophyl l b also present. Chlorophyll a concentration in sediments under the t ables was 207 mg m(-2) (CV=73%) and 895 mg m(-2) (CV=28%) in reference sediments; the stock of plant pigments was increased under the tables by biodeposition. Microphytobenthos constitutes a compartment with an important contribution in biomass, but also in oxygen production. (C) 1997 Academic Press Limited.