Seasonal dynamics of transparent exopolymer particles (TEP) and their drivers in the coastal NW Mediterranean Sea.

Transparent Exopolymer Particles (TEPs) are a subclass of organic particles with high impact in biogeochemical and ecological processes, such as the biological carbon pump, air-sea interactions, or the microbial loop. However, the complexity in production and consumption makes TEP dynamics hardly predictable, calling for the need of descriptive studies about the in situ dynamics of these particles. We followed monthly TEP dynamics and combined them with a dataset of environmental variables during three years in a coastal site of the oligotrophic North Western Mediterranean (Blanes Bay). TEP concentration, ranging from 11.3 to 289.1μgXGeqL-1 (average 81.7±11.7μgXGeqL-1), showed recurrent peaks in early summer (June-July). TEP were temporally disconnected from chlorophyll a maxima, that occurred in late winter and early spring (maxima 1.21μgL-1), but they were significantly related to the abundance of specific phytoplankton groups (diatoms and dinoflagellates) and also coincided with periods of low nutrient concentrations. The fraction of particulate organic carbon in the form of TEP (the TEP:POC and TEP:PM ratios) were also highest in early summer, indicating that TEP-enriched particles of low density accumulate in surface waters during stratified periods. We hypothesize that the accumulation of these particles affects the microbial food web by enhancing the activity of specific prokaryotic extracellular enzymes (esterase, β-glucosidase and alkaline phosphatase) and promoting the abundance of heterotrophic nanoflagellates.