Role of environmental factors for the vertical distribution (0–1000 m) of marine bacterial communities in the NW Mediterranean Sea

J F Ghiglione,M Pujo-Pay,C Palacios,G Mével,M Goutx,C Labrune,N Garcia,J C Marty,P Conan

doi:10.5194/bg-5-1751-2008

Abstract

Abstract. Bacterioplankton plays a central role in energy and matter fluxes in the sea, yet the factors that constrain its variation in marine systems are still poorly understood. Here we use the explanatory power of direct multivariate gradient analysis to evaluate the driving forces exerted by environmental parameters on bacterial community distribution in the water column. We gathered and analysed data from a one month sampling period from the surface to 1000 m depth at the JGOFS-DYFAMED station (NW Mediterranean Sea). This station is characterized by very poor horizontal advection currents which makes it an ideal model to test hypotheses on the causes of vertical stratification of bacterial communities. Capillary electrophoresis single strand conformation polymorphism (CE-SSCP) fingerprinting profiles analyzed using multivariate statistical methods demonstrated a vertical zonation of bacterial assemblages in three layers, above, in or just below the chlorophyll maximum and deeper, that remained stable during the entire sampling period. Through the use of direct gradient multivariate ordination analyses we demonstrate that a complex array of biogeochemical parameters is the driving force behind bacterial community structure shifts in the water column. Physico-chemical parameters such as phosphate, nitrate, salinity and to a lesser extent temperature, oxygen, dissolved organic carbon and photosynthetically active radiation acted in synergy to explain bacterial assemblages changes with depth. Analysis of lipid biomarkers of organic matter sources and fates suggested that bacterial community structure in the surface layers was in part explained by lipids of chloroplast origin. Further detailed analysis of pigment-based phytoplankton diversity gave evidence of a compartmentalized influence of several phytoplankton groups on bacterial community structure in the first 150 m depth.

Highlights

Microorganisms represent the most abundant, biogeochemically important biological component in the oceans
Capillary electrophoresis single strand conformation polymorphism (CE-SSCP) fingerprinting profiles analyzed using multivariate statistical methods demonstrated a vertical zonation of bacterial assemblages in three layers, above, in or just below the chlorophyll maximum and deeper, that remained stable during the entire sampling period
Through the use of direct gradient multivariate ordination analyses we demonstrate that a complex array of biogeochemical parameters is the driving force behind bacterial community structure shifts in the water column

Summary

Introduction

Microorganisms represent the most abundant, biogeochemically important biological component in the oceans. The application of molecular techniques to microbial ecology has led to an increased appreciation of bacterial community changes with depth as demonstrated in a wide variety of oligotrophic seawaters, including the Pacific and Atlantic Oceans (Lee and Fuhrman, 1991), the Mediterranean Sea (Acinas et al, 1997; Moeseneder et al, 2001; Ghiglione et al, 2005, 2007), the Arabian Sea (Riemann et al, 1999) and Antarctic zones (Murray et al, 1998). The presence of the same pattern in such widely distant ocean basins suggests that vertical stratification is a very important factor determining the bacterial species inhabiting the ocean (Acinas et al, 1997)

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Discussion

Conclusion