Aquaculture America 2023

February 23 - 26, 2023

New Orleans, Louisiana USA


Julie E. Le Ray*, Béatrice L. Bec, Annie Fiandrino, Lauryn Olla, Franck Lagarde, Nicolas Cimiterra, Vincent Ouisse, Sylvain Rigaud, Julie Régis, Marion Richard


MARBEC, Univ Montpellier, CNRS, IRD, Ifremer, Sète, France


Anoxic crisis are recurrent in the Thau lagoon, a Mediterranean lagoon exploited by shellfish farming. For this experiment, we investigated the triggering and consequences of anoxia in function of the benthic compartment. The use of in situ benthic mesocosms made it possible to confine the lagoon waters with or without macrophytes. Oxygen dynamics, nutrient and H2S concentrations, bacterial abundances and phytoplankton community structure were studied during 11 days near the bare sediment, Halopithys, and Zostera community. These were the main species found under oyster rearing table.

The responses from the different benthic communities, were highly contrasted according to the community. Near the bare sediment, hypoxic conditions were observed for four days, then concentration went back up. In presence of Halopithys, the system switched to anoxia, raising significantly NH4+ and PO43- concentrations (respectively: 57.8 µmol·l-1 on day 7 and 13.06 µmol·l-1 on day 11). High bacterial abundances were measured (14.55 x 106 cells·ml-1, on days 4, 5 and 6), but the phytoplanktonic biomass lowered (final concentration: 0.33 µgChla·l-1). In presence of Zostera, oxygen levels stayed above hypoxic levels, even during the night. They were the most resistant community among the three treatments.

These results highlight the importance of monitoring and restoring seagrass meadows in lagoonal ecosystems. This is especially important when the lagoon is exploited by aquacultural activities making then more prone to anoxic crisis and mass mortalities.