Seasonal dynamics of extracellular polymeric substances (EPS) in surface sediments of a diatom-dominated intertidal mudflat (Marennes–Oléron, France)

Abstract

Numerous field-based investigations have highlighted that the production of extracellular polymeric substances (EPS) is physico-chemically and ecologically important for intertidal mudflats. EPS are largely secreted by marine benthic diatoms and their quantity and quality are environmental-dependant. This paper focused on the dynamic pathways, concentration rates and monosaccharides composition of colloidal, bound and residual carbohydrates extracted by using a cationic exchange resin from a diatom-dominated intertidal mudflat (Marennes–Oléron, France) during two different sampling periods: winter (February 2008) and summer (July 2008). A wide range of biotic and abiotic parameters were also studied to better understand the effect of environmental parameters, e.g., chlorophyll a, salinity, pore water amount, emersion time, luminosity, C:N ratio and tidal coefficient. Multiple colorimetric assays coupled to gas chromatographic analyses were carried out to perform the biochemical characterizations. Firstly, the quantity of carbohydrates produced during winter (5.28μg·μgchl a−1) was more important than during summer (2.04μg·μgchl a−1). Yet, more proteins were found during summer for the colloidal and bound fractions (0.73 and 1.04μg·μgchl a−1). Further investigations showed that the dynamic pathways were equivalent between winter and summer: bound carbohydrates (BC) quantities increased during the sediment emersion periods on the contrary to colloidal carbohydrates (CC) which tended to drop throughout the emersion time. The quality in monosaccharides was fraction-dependant, whatever the season. CC were always glucose-rich confirming their role of carbon source. BC were mainly composed of rhamnose whose the ratio increased during the emersion period, thus conferring adhesive properties to the extracellular matrix bounding diatoms cells. Residual carbohydrates (RC) were composed of various monosaccharides and a major increase of glucose content was found at the end of emersion, corresponding to intracellular C-storage in prevention to immersion times. Summer-RC were composed of fucose, a monosaccharide specific to these fractions and which was non-present during the winter campaign. Environmental parameters, such as salinity, pore water amount, and tidal coefficient could have a significant impact on the concentration rates and pathways of carbohydrates.