T-MEDNet: a collaborative network to track mass mortality events in the Mediterranean Sea

The Mediterranean region is a climate change hotspot. According to the United Nations Environment Program - Mediterranean Action Plan (UNEP/MAP), the region is warming at a rate of 20% faster than the global average, with repeated periods of drought and heatwaves alternating with intense rains and storms. While land and very shallow coastal habitats are well monitored by environmental agencies in some Mediterranean countries, the ability to observe and understand the phenomena occurring in deeper coastal waters remains very limited. Since the first observations of mass mortality events (MMEs) linked to marine heatwaves (MHWs) occurred in 1999, the establishment of T-MEDNet, a collaborative observation network, has been pivotal in tracking anthropogenic climate change impacts on marine coastal ecosystems. To address the lack of high-resolution temperature series in Mediterranean coastal habitats, T-MEDNet adopted a standardized protocol based on underwater temperature data loggers, gradually engaging researchers from various institutions and countries. Presently, the network boasts over 33 teams of scientific divers from 11 Mediterranean countries acquiring temperature data and conducting regular monitoring on MMEs. This enables detailed analyses of the relationship between MHWs and MMEs, enhancing our understanding of the consequences of climate change on benthic communities. Thanks to the collaborative research efforts, T-MEDNet compiled the most comprehensive database on MMEs. They mainly affected species dwelling between 0 and 40 m. The number of species affected has increased over the last two decades, involving more than 90 species belonging to 10 phyla. Cnidaria, Porifera and Bryozoa account for the largest number of the impacted species. This knowledge is critical for developing strategies to enhance the resilience of native biodiversity, ecosystem functioning and services. Yet, the network’s maintenance and expansion into unmonitored areas demand an escalating and continued collaborative effort.