What is
T-MEDNet?

Climate change effects such as shifts in species distribution and mass mortality events have been related to the warming trend observed in the Mediterranean Sea. However, despite the notable exceptions of very few long-term series, there was an enormous gap of knowledge on temperature conditions in coastal waters as well as on ecological effects, which hindered an in-depth analysis of climate change impacts on marine coastal biodiversity.

Since obtaining representative data sets on in situ thermal regimes is crucial to describe the marine environment and analyze impacts. Late in the 1990s, Dr. J.G. Harmelin (Centre d'Océanologie de Marseille) set up the first temperature surveys using autonomous data loggers at three depths (1, 24 and 42 m) in the Marseille area (France). Since then, temperature surveys have been progressively extended to a growing number of sites using the same data loggers and protocols for continuous long-term monitoring, generally at standard depths, every 5 m from the surface to 40 m depth or more.

To date, T-MEDNet involves more than 30 public research institutions and 30 MPAs from 11 Mediterranean countries, under the scientific coordination of the Institute of Marine Sciences (ICM-CSIC). Continuous T-series are now undertaken in +70 sites, resulting in a unified quality checked database of more than 20 million T-samples. Furthermore, T-MEDNet is contributing to track the mass mortality events and shifts in species distribution, the main ecological effects of marine heatwaves and warming, in more than climate change are being monitored in 150 areas across the Mediterranean resulting in the most comprehensive datasets on ecological climate change impacts.

The implementation of these monitoring activities proved to be crucial for increasing our detection, understanding and forecasting abilities on climate change effects in Mediterranean coastal ecosystems.

These abilities will be key to develop realistic climate change impacts and vulnerability assessments and implement sound management plans for the conservation of the rich Mediterranean biodiversity.

T-MEDNet data base allowed for the very first time the characterization of the coastal waters (5-40 m) local stratification dynamics from hours to years. In the NWM, contrasted conditions are experienced by coastal benthic communities at different spatial scales.

Not only under the influence of general circulation, but also due to local topography, bathymetry and wind driven processes such as upwellings (top and bottom right) or downwellings (bottom left). Contrarily, in the Balearic islands, stable and deep stratification prevails.

T-MEDNet data base has been crucial for the analysis of the inter annual variability of coastal waters (5-40 m) stratification dynamics under various climatic forcings, including the regional heatwaves of summers 2003 and 2006 (the warmest August and July over France since 1950 respectively).

In 2006, the strong climatic anomaly resulted in contrasted seawater stratification patterns depending on localities. The high resolution temperature series also allowed to better characterize warm conditions as shown here with the number of days above 23 and 25 °C. Years during which mortality events occured are shown in red.

T-MEDNet climatic series have already been used to evaluate 3D hydrodynamical models in coastal areas over a range of hydroclimatic conditions. So far, MARS3D-MENOR and -RHOMA realistic models developed by IFREMER benefited of this evaluation, showing for instance, that in the Marseille area, upwelling process and annual cycle are quite well reproduced by the simulations.

Qualification of the high resolution model MENOR that covers a vast domain are being conducted for all T-MEDNet available sites and years. Overall, together with dedicated simulations work, this should permit to better anticipate impact of climate change on coastal habitats and ecosystems.