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Aquatic Microbial Ecology

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AME 26:235-246 (2002)  -  doi:10.3354/ame026235

Low grazing impact of mesozooplankton on the microbial communities of the Alboran Sea: a possible case of inhibitory effects by the toxic dinoflagellate Gymnodinium catenatum

Albert Calbet*, Elisabetta Broglio, Enric Saiz, Miquel Alcaraz

Institut de Ciències del Mar, CMIMA (CSIC), Departament de Biologia Marina i Oceanografia, P. Marítim de la Barceloneta 37-49, 08003 Barcelona, Catalunya, Spain

ABSTRACT: The grazing impact of the mesozooplankton community on algae and protozoans was assessed during September 1999 in the Alboran Sea (SW Mediterranean). Ingestion rates were obtained by incubating aliquots of net-collected mesozooplankton with natural seawater. The results showed a weak pressure of mesozooplankton on algae and protozoans, with grazing impacts on community stocks averaging 1.3, 1.4 and 1.5% for phytoplankton, ciliates and dinoflagellates, respectively. Chlorophyll a (chl a) >5 μm was grazed at higher rates than chl a <5 μm, and in some stations dinoflagellates were preferred over ciliates. In general, ingestion rates were low, yielding to daily rations ranging from 2 to 20% of body carbon, which were too low to cover the metabolic demand of mesozooplankton in most of the stations. We hypothesize that this unexpected result could be in relation to the presence of the toxic dinoflagellate Gymnodinium catenatum in the study area.

KEY WORDS: Mesozooplankton · Phytoplankton · Ciliates · Dinoflagellates · Gymnodinium catenatum · Ingestion · Grazing · Alboran Sea

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