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 (similar to 29 degrees N to similar to 40 degrees 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 0.8 mg m(-3), the abundance of heterotrophic bacteria varied between <1.0 x 10(5) and >1.0 x 10(6) cells ml(-1), and that of heterotrophic nanoflagellates between <100 and >1.0 x 10(4) cells ml(-1). The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24 mu gC L-1 d(-1); and the growth rates were in the range <0.01-2.1 d(-1). In the Latitud-II cruise, Prochlorococcus ranged between <10(3) and >3 x 10(5) cells ml(-1), Synechococcus between <100 and >1.0 x 10(4) cells ml(-1), and picoeukaryotes between <100 and >10(4) cells ml(-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. (C) 2008 Elsevier Ltd. All rights reserved,