Since November 2023, the MAHEWA project has been conducting monthly monitoring of the Southwest Lagoon to evaluate the impact of marine heatwaves on lagoon ecosystems. This monitoring spans from Anse Vata Bay to the Dumbéa Pass and relies on a network of 17 stations where key physical and biological parameters are measured: temperature, salinity, oxygen, fluorescence, turbidity, and pH, using CTD probes and fixed sensors.
Among these stations, six are sampled for water at a 1-meter depth to extract environmental DNA (eDNA), enabling analysis of microbial biodiversity (protists, archaea, and bacteria). Additionally, passive sensors are deployed on several reefs (Maître Islet, Crouy Reef, and Aboré Reef) to study the diversity of benthic microalgae and marine phycotoxins, particularly those linked to ciguatera.
Every three months, samples of herbivorous and carnivorous fish, as well as filter-feeding mollusks, are collected to identify the presence of phycotoxins in their tissues, thereby assessing the risks of foodborne intoxications.
The collected data will help validate satellite observations by reconstructing the history of marine heatwaves in Caledonian lagoons. This research will also enhance understanding of the responses of microorganisms and phycotoxins to extreme warming events, and improve anticipation of their impacts on biodiversity and marine resources.
Photo : IFREMER/IRD Team at Sea on the Archamia (Oriane, Thierry, Jordi)
