Bacterial biomass, heterotrophic production and utilization of dissolved organic matter photosynthetically produced in the Almeria-Oran front

Abstract

Bacterial biomass, bacterial production and the quantitative importance of the heterotrophic assimilation of photosynthetically produced dissolved organic carbon (PDOC) were examined in relation to the hydrodynamical and biological conditions in the Almeria-Oran front area (Alboran Sea, Western Mediterranean). Although, including all data, bacterial abundance correlated with chlorophyll a ( r = 0.49), the bacteria/phytoplankton carbon ratio decreased in the core of the Atlantic jet. Bacterial integrated secondary production ranged from 124 to 199 mg C m −2 d −1. Bacterial generation times averaged 3.2 d (S.D.= 1.3) in frontal sites above the pycnocline and 25 d (S.D. = 11) under the pycnocline. In the adjacent Mediterranean waters, bacterial generation times displayed homogenous values from the surface to 150 m (mean 2.7;d; S.D. = 1.5). An isolated Atlantic water mass, at the right side of the jet, showed the longest average bacterial generation times (9.5 d). In the chlorophyll maximum layers, percent extracellular release represented 23.5% of total net primary production in the oligotrophic sites and only 6.5% in the core of the Atlantic jet. The contribution of PDOC to bacterial production exhibited large variations (17–100%). Dissimilarities among sites and hydrodynamical structures of the water masses were mostly observed in bacterial generation times and phytoplankton extracellular release.