Microbiomass structure and respiratory activity of microneuston and microplankton in the northwestern Mediterranean Sea influenced by Rhone river water

Abstract

Surface microlayers collected in the northwestern Mediterranean Sea showed significant enrichment of particulate organic carbon (POC), ATP, chlorophyll, muramic acid (a specific bacterial biomass indicator) and total and viable bacterial count. Mean enrichment factors for muramic acid (52.6) and total bacterial count (38.4) were clearly higher than that for chlorophyll (19.8). Although phyto- and bacterioneuston appeared to have lower ATP levels, particularly in brackish water areas, compared with plankton, the bacterioneuston exhibited higher viability than bacterioplankton found in the corresponding underlying waters. Biochemical Oxygen Demand (BOD) and Electron Transport Systems (ETS) measurements clearly showed enhanced respiratory acitivities (up to 765.1 mu l O2/l h) in the microlayers compared to underlying bulk waters. Data comparison between BOD, ETS, POC, salinity and microbiomass estimates suggests that the measured respiratory activities (BOB and ETS) were well associated with bacterial populations in both the microlayer and bulk waters.