| Summary: | A comprehensive study of the ecology and photosynthetic activity of a newlydiscovered Vaucheria sp. dominated arctic microphytobenthos was addressed here. The microphytobenthos is a very diversified community of microscopic organisms from the surficial sediment of aquatic ecosystems. It typically consists of various assemblages of substrate-dwelling photosynthetic diatoms, cyanobacteria, flagellates and algae. The microphytobenthos plays a central ecological role in estuarine environment, responsible for a significant fraction of the total primary production, mediating water-sediment nutrient exchanges, enhancing benthic-pelagic coupling and efficiently stabilizing the sediment. Despite their ecological value in coastal areas, very little is known about arctic microphytobenthos ecology and photosynthetic performances. Across the arctic coastline, where large inter-seasonal variations in light, temperatures and nutrient levels are experienced along with increasing pressures, microbenthic communities have shown signs of excellent metabolic adaptations. In case, across this arctic tidal flat, Vaucheria sp. was found to show a remarkable adaptation to the local ecological parameters. We demonstrated in this ecosystem the strong impacts of both marine and freshwater co-occurrences creating Vaucheria sp. environment. The heterogeneity of Vaucheria sp. habitat was described. Locally, the water column was phosphorus-limited and a temporal shift from phosphorous to silica-limited conditions occurred throughout the sampling period, witnessing of the highly dynamic nature of this tidal ecosystem. At the ecosystem level, the strong microphytobenthos’ photosynthesis was supported by significant high water-pH values, correlated to Vaucheria sp. spatial occurrence. Even though Vaucheria sp. seemed to dominate, we found evidences of a more complex micro-phytobenthic community functioning. Vaucheria sp. community exhibited adaptability to large variations in abiotic factors. Gasometric and Chlorophyll fluorescence measurements ...
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