Gulf of Maine microplankton during 1987: Abundance, biovolume, biomass and production estimates

From February to August, 1987, preserved water column samples from six Gulf of Maine cruises were examined for microplanktonic (5-200 ;In general, diatoms were numerically dominant both nearshore and offshore, reaching maximum abundances in July (10;Nontintinnid ciliates dominated near- and offshore biomass from March to May, attaining a maximum offshore biomass of 38.2 ;Production estimates were determined from the literature and near- and offshore Gulf of Maine microplankton food web models were derived. Production by ciliates and heterotrophic dinoflagellates represented 64% of the metazoan food requirement in offshore and 43% in nearshore waters. Production estimates agreed with laboratory growth rate experiments done on Mesodinium sp. (possibly M. pulex).;Heterotrophic microplankton were found to occupy an important intermediate position in the Gulf of Maine's nearshore and offshore food webs. Findings from this study support a rethinking of the "primary production" concept in marine environments, and promote further research into the ecological role of heterotrophic microplankton.