Abstract
The autotrophic plankton assemblage along the subtropical coastal embayments of the South Brazil Bight is dominated by the cyanobacteria Synechococcus. This investigation evaluated the contribution of photosynthetic carbon fixation to the total Carbon metabolism within the planktonic system of Mamangua Ria, a sub-system of the Bay of Ilha Grande, southeast Brazilian coast. Our results reveal the Carbon budget inside the Ria is not balanced by autotrophic production. Net community production is generally negative throughout the year, with a deficit ranging from 0.5 to 1.5 mg m-2 d-1 below what is necessary to sustain the local plankton ecosystem. We argue that the offset between daily primary production and heterotrophic Carbon consumption may be balanced by grazing of nano-heterotrophs on heterotrophic bacteria. Our conclusions apply to the majority of the Brazilian inner shelf waters outside of estuarine plumes and upwelling systems, thus with meso-oligotrophic conditions
Highlights
Coastal waters constitute less than 10% of the total oceanic area, yet account for ca 25% of the global oceanic primary production (Berger et al, 1989)
The carbon biomass stocked in heterotrophic bacteria may return to the classic food chain through bacterivory by microheterotrophs which in turn may be predated by larger zooplankton
C-14 uptake experiments were conducted in the Bay of Ubatuba (Teixeira, 1973; Teixeira and Gaeta, 1991; Gaeta et al, 1995, 1999) south of the Mamanguá Ría, which according to Ikeda and Stevenson (1980) is dynamically connected with the BIG through coastal water circulation
Summary
Coastal waters constitute less than 10% of the total oceanic area, yet account for ca 25% of the global oceanic primary production (Berger et al, 1989). The carbon biomass stocked in heterotrophic bacteria may return to the classic food chain through bacterivory by microheterotrophs (e.g., flagellates and ciliates) which in turn may be predated by larger zooplankton. This alternate trophic pathway, a microbial loop (sensu Azam et al, 1983), drives back the excreted dissolved organic matter toward the classic food chain. Detritus sedimentation, and/or advection are additional losses of organic carbon that are more difficult to assess quantitatively
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