Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6383592 | Deep Sea Research Part I: Oceanographic Research Papers | 2015 | 43 Pages |
Abstract
The response of planktonic heterotrophic prokaryotes to the NW Mediterranean winter-spring offshore phytoplankton bloom was assessed in 3 cruises conducted in March, April-May and September 2009. Bulk measurements of phytoplankton and bacterioplankton biomass and production were complemented with an insight into bacterial physiological structure by single-cell analysis of nucleic acid content [low (LNA) vs. high (HNA)] and membrane integrity (“Live” vs. “Dead” cells). Bacterial production empirical conversion factors (0.82±0.25 SE kg C mol leucineâ1) were almost always well below the theoretical value. Major differences in most microbial variables were found among the 3 periods, which varied from extremely high phytoplankton biomass and production during the bloom in March (>1 g C mâ2 dâ1 primary production) to typically oligotrophic conditions during September stratification (<200 mg C mâ2 dâ1). In both these periods bacterial production was ~30 mg C mâ2 dâ1 while very large bacterial production (mean 228, with some stations exceeding 500 mg C mâ2 dâ1) but low biomass was observed during the April-May post-bloom phase. The contribution of HNA (30-67%) and “Live” cells (47-97%) were temporally opposite in the study periods, with maxima in March and September, respectively. Different relationships were found between physiological structure and bottom-up variables, with HNA bacteria apparently more responsive to phytoplankton only during the bloom, coinciding with larger average cell sizes of LNA bacteria. Moderate phytoplankton-bacterioplankton coupling of biomass and activity was only observed in the bloom and post-bloom phases, while relationships between both compartments were not significant under stratification. With all data pooled, bacteria were only weakly bottom-up controlled. Our analyses show that the biomass and production of planktonic algae and bacteria followed opposite paths in the transition from bloom to oligotrophic conditions.
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Authors
Ana Gomes, Josep M. Gasol, Marta Estrada, Leticia Franco-Vidal, Laura DÃaz-Pérez, Isabel Ferrera, Xosé Anxelu G. Morán,