Microbial Functioning and Community Structure Variability in the Mesopelagic and Epipelagic Waters of the Subtropical Northeast Atlantic Ocean

8 pages, 7 figures, 1 table

We analyzed the regional distribution of bulk heterotrophic prokaryotic activity (leucine incorporation) and selected single-cell parameters (cell viability and nucleic acid content) as parameters for microbial functioning, as well as bacterial and archaeal community structure in the epipelagic (0 to 200 m) and mesopelagic (200 to 1,000 m) subtropical Northeast Atlantic Ocean. We selectively sampled three contrasting regions covering a wide range of surface productivity and oceanographic properties within the same basin: (i) the eddy field south of the Canary Islands, (ii) the open-ocean NE Atlantic Subtropical Gyre, and (iii) the upwelling filament off Cape Blanc. In the epipelagic waters, a high regional variation in hydrographic parameters and bacterial community structure was detected, accompanied, however, by a low variability in microbial functioning. In contrast, mesopelagic microbial functioning was highly variable between the studied regions despite the homogeneous abiotic conditions found therein. More microbial functioning parameters indicated differences among the three regions within the mesopelagic (i.e., viability of cells, nucleic acid content, cell-specific heterotrophic activity, nanoflagellate abundance, prokaryote-to-nanoflagellate abundance ratio) than within the epipelagic (i.e., bulk activity, nucleic acid content, and nanoflagellate abundance) waters. Our results show that the mesopelagic realm in the Northeast Atlantic is, in terms of microbial activity, more heterogeneous than its epipelagic counterpart, probably linked to mesoscale hydrographical variations

This research was supported by the Spanish “Plan Nacional de I D” (MEC) under the RODA (CTM2004-06842-C03-03/MAR) and CAIBEX (CTM2007-66408-C02-02) grants to J.A.; a grant of the Earth and Life Science Division of the Dutch Science Foundation (ALW-NWO; ARCHIMEDES project, 835.20.023) to G.J.H.; and a predoctoral Fellowship of the Spanish Ministry of Education and Science (AP2005-3932) and a postdoctoral grant under the MOCA (European Science Foundation – Eurocores Program Evolutionary and Ecological Functional Genomics) project to F.B. Projects MODIVUS (CTM2005-04795/MAR) and STORM (CTM2009-09352/MAR) supported J.M.G. We thank the captain and crew of R/V BIO Hespérides for their support at sea and M. Espino for the determination of nanoflagellate abundances

Peer reviewed