Microbial plankton abundance and heterotrophic activity across the Central Atlantic Ocean

Abstract: The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator–prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean (∼29°N to ∼40°S). Latitud cruises were performed in 1995 between March–April and October–November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8mgm−3, the abundance of heterotrophic bacteria varied between <1.0×105 and >1.0×106 cellsml−1, and that of heterotrophic nanoflagellates between <100 and >1.0×104 cellsml−1. The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24μgCL−1 d−1; and the growth rates were in the range <0.01–2.1d−1. In the Latitud-II cruise, Prochlorococcus ranged between <103 and >3×105 cellsml−1, Synechococcus between <100 and >1.0×104 cellsml−1, and picoeukaryotes between <100 and >104 cellsml−1. Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto- and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic Ocean. [Copyright &y& Elsevier]