Effects of physical forcing on COastal ZOoplankton community structure: study of the unusual case of a MEDiterranean ecosystem under strong tidal influence (Project COZOMED-MERMEX).

Abstract

International audienceThe COZOMED-MERMEX project aims at understanding how hydrodynamic forcing (currents, tides, winds)combine with anthropogenic forcing and climate to affect the variability of coastal Mediterranean zooplanktoncommunities under contrasting tidal influence. This study includes (i) a zero state of knowledge via a literaturereview of existing data and (ii) a case study on the system Boughrara lagoon - Gulf of Gabes. This ecosystemgives major services for Tunisia (about 65% of national fish production) but is weakened by its situation in aheavily anthropized area and under influence of urban, industrial and agricultural inputs. Besides this regionis subject to specific climate forcing (Sahelian winds, scorching heat, intense evaporation, flooding) whichpossible changes will be considered. The expected issues are (i) to improve our knowledge of hydrodynamicforcing on zooplankton and ultimately on the functioning of coastal Mediterranean ecosystems impacted byanthropogenic and climatic effects and (ii) to elaborate management tools to help preserving good ecologicalstatus of these ecosystems: hydrodynamic circulation model, mapping of isochrones of residence times, mappingof the areas of highest zooplankton abundances (swarms), and sensitive areas, etc. This project strengthensexisting scientific collaborations within the MERMEX program (The MerMex Group, 2011) and in the frameof an international joint laboratory (COSYS-Med) created in 2014. A first field mulidisciplinary campaign wasperformed in October 2016. The strategy combined measurements of sea level and currents (mooring of ADCP,Argonaute and tidal gauges), hydrological description of water masses (horizontal and vertical transect with aMinibat equipped with CTD, fluorescence and turbidity sensors) and discrete sampling of nutrients, DOC, POC,pico, nano, microphytoplankton and mesozooplankton. The first results allow a description of water currents andshows a good coupling between tidal cycles (ebb-flood and spring tide neap tide) and the dynamics of planktoniccompartments in the lagoon