Spatial and temporal dynamics of nano- and pico-size particulate organic matter (POM) in a coastal megatidal marine system

Surface water samples of size selected seston (0.7-20μm) were collected from April to September 2013 at three similar coarse-sand benthic habitats, characterized by Glycymeris glycymeris and congregations of Venus verrucosa. Additionally, seston sampling was performed at a fixed location throughout a complete tidal cycle (2014). A combination of fatty acid, isotope, and flow cytometry analyses were used to determine the quality and quantity of nano- and pico-sized particulate organic matter (POM). High variability was found between fatty acid replicate samples. Similar temporal patterns were observed at two sheltered sites, while the exposed site displayed less pronounced seasonal changes. Lower concentrations of 16C and 18C polyunsaturated fatty acids (PUFA) were found during low tide sampling. Isotope enrichment factors suggest that bivalve feeding at Chausey was maximal during ebb tide. Globally, POM was dominated by picoeukaryotes, with concentrations exceeding 50,000 cells/mL, and (16:4ω3+18:3ω3)/Σω3 is proposed as novel biomarker of picoeukaryotes in this region.