Structures of benthic prokaryotic communities and their hydrolytic enzyme activities resuspended from samples of intertidal mudflats: An experimental approach

21 Resuspended sediment can increase plankton biomass and the growth of bacteria, thus 22 influence the coastal planktonic microbial food web. But little is known about resuspension 23 itself: is it a single massive change or a whole series of events and how does it affect the 24 quantity and quality of resuspended prokaryotic cells? We simulated the sequential erosion of 25 mud cores to better understand the fate and role of benthic prokaryotes resuspended in the 26 water column. We analyzed the total, attached and free-living prokaryotic cells resuspended, 27 their structure and the activities of their hydrolytic enzymes in terms of the biotic and abiotic 28 factors that affect the composition of microphytobenthic biofilm. 29 Free living prokaryotes were resuspended during the fluff layer erosion phase (for shear 30 velocities below 5 cm.s -1 ) regardless of the bed sediment composition. At the higher shear 31 velocities, resuspended prokaryotes were attached to particulate matter. Free and attached 32 cells are thus unevenly distributed, scattered throughout the organic matter (OM) in the 33 uppermost mm of the sediment. Only 10-27% of the total cells initially resuspended were 34 living and most of the Bacteria were Cyanobacteria and Gamma-Proteobacteria; their 35 numbers increased to over 30% in parallel with the hydrolytic enzyme activity at highest 36 shear velocity. These conditions released prokaryotic cells having different functions that lie 37 deep in the sediment; the most important of them are Archaea. Finally, composition of 38 resuspended bacterial populations varied with resuspension intensity, and intense 39 resuspension events boosted the microbial dynamics and enzyme activities in the bottom 40 layers of sea water. 41