Bacterial activity and diffusive nutrient supply in the oligotrophic Central Atlantic Ocean

Abstract

Growing evidence of inorganic nutrient limitation on oceanic bacteria suggests a global dependence of bacterial activity and production on rates of nutrient supply. The present study examined whether surface bacterial abundance is significantly related to water column stability, and whether bacterial activity and growth rate are related to the rate of diffusive supply of inorganic nutrients to the mixed layer in the Central Atlantic during 2 meridional cruises. The 2 cruises were run under very different oceanic conditions, with relatively low values of bacterial activity in spring 1995 and relatively higher values in fall 1995. We obtained depth-resolved data in the second cruise and found that the integrated value of bacterial production was also related to the rate of nutrient supply, while integrated particulate primary production and chlorophyll concentration were not. There was also no relationship between particulate primary production and bacterial production. The relationship between nutrient supply and integrated bacterial production was tested with data from a mesocosm experiment showing a good fit to the pattern obtained in the Atlantic. Average bacterial production was ~21% of primary production in the Central Atlantic, with values ranging between 5 and 100%, and higher values in the tropical areas. The demonstration of a direct relationship between nutrient supply and bacterial activity helps to explain a relatively large bacterial biomass as compared to phytoplankton biomass, a low bacterial growth efficiency, and a high bacterial carbon demand relative to contemporaneous primary production often measured in the open ocean, as well as the accumulation of dissolved organic carbon (DOC) observed in nutrient-limited oligotrophic seas.

High bacterial carbon demand and low growth efficiency at a tropical hypereutrophic estuary: importance of dissolved organic matter remineralization

“…Indeed, previous studies performed in tropical estuarine waters showed lower BR rates (BR max =0.7 µM C h LEE et al, 2009;RAM et al, 2003). Nutrient availability also plays a major role in regulating bacterial carbon metabolism (ASMALA et al, 2014;BERGGREN et al, 2010;GASOL et al, 2009;KEMP, 2003). Bacterial uptake of DOM follows a rather constant ratio: C:N:P ~ 50:10:1 (FAGERBAKKE et al, 1996;GOLDMAN et al, 1987).…”

Nutrient supply controls picoplankton community structure during three contrasting seasons in the northwestern Mediterranean Sea

“…Similar patterns were described by Corno et al (2007), who used lower euphotic zone stratification to describe patterns in the composition of the picoplankton community at the ALOHA time-series station. As far as we know, previous studies that focused on the relationship between bacterial abundance and nutrient supply are limited to the study by Gasol et al (2009), who described a positive relationship between water column stratification and heterotrophic bacterial abundance.…”

Global-scale distributions of marine surface bacterioplankton groups along gradients of salinity, temperature, and chlorophyll: a meta-analysis of fluorescence in situ hybridization studies

“…1B & 1C in Table 4), indicating a lower response of bulk bacterial abundance to increasing phytoplankton biomass in oligotrophic conditions (i.e. Gasol & Duarte 2000, Gasol et al 2009). Whilst bacterial community structure was not analyzed in these previous studies, one can consider that such low slopes found at the bulk level in offshore systems may indicate that the bacterial groups exhibiting similar weak regression slopes would be those mainly driving the relationship.…”

“…This would in turn support the idea proposed by Yokokawa & Nagata (2005) that particular ecological traits (DOC uptake, bacterial production and growth, grazing rates) can be detected using broad phylogenetic probes, when an ecological trait of a broad group largely reflects the trait of the dominant subgroup in the community. Low coupling between SAR11 and chl a might also indicate the use by this dominant bacterial group in oceanic waters of non-contemporaneous primary production, something that has been suggested to occur for the bulk community across the central Atlantic gyre (Gasol et al 2009). …”