From biological traits to ecosystem functions: a trait-based approach

English. The biological community inhabiting the sediment, the macrobenthos, is a vital and key component of the marine ecosystem. Through their biological activities, benthic animals rework the sediment in a process termed bioturbation. Bioturbation have a great impact on the benthic-pelagic coupling by modifying the gradients of geochemical properties, redistributing food and affecting the exchanges of solutes and gases with the overlaying water. However, so far, ocean models ignore the life at the sea floor and its impact on biogeochemical cycles and ecosystem functioning. Here, we propose to introduce the variability of the biological communities in an ocean model (NEMO4.2-BAMBHI), run in an operational mode by the CMEMS Black Sea Marine Forecasting center. We use a functional approach of the benthic biodiversity meaning that species are defined by their characteristics (e.g. dwelling depth, mobility) with an effect on ecosystem functioning (i.e. effect trait). We compile a macrozoobenthos dataset from 138 sampling stations covering the northwestern shelf of the Black Sea. Firstly, we determine traits related to bioturbation (e.g. burrowing depth and mobility in the sediment) for the most abundant taxa as a proxy of the macrobenthic species influence on ecosystem functioning. Then, we assess trait values present in the community for each sampling sites based on species observation and their derived traits. From punctual values, we derive continuous distribution of traits modalities over the whole shelf using interpolation tool. We show that deeper burrowing depth as well as higher mobility are found near the mouth of the Danube Delta where higher concentrations of suspended materials and nutrients are observed. At the edge of the shelf, where intrusions of anoxic waters occur, the potential of bioturbation is much reduced. Thanks to these maps of traits, that will be provided in the framework of NECCTON project, the variability of macrobenthos functions will be integrated in the parametrization of NEMO4.2-BAMBHI model. This innovative and appropriate representation of the benthic-pelagic coupling in a 3D ocean model will better predict at large scales the contribution of marine sediments to carbon sequestration, deoxygenation, nitrogen removal through denitrification at large scales.

14. Life below water