The bigger European artificial reef is from Marseille

Innovation for marine biodiversity: the world-renowned Cortiou artificial reef

Marseilles is home to the largest artificial reef in the Mediterranean, but also in Europe, and is recognized worldwide as an innovation for marine biodiversity. Do you know the history behind this gigantic installation?

Until the end of the 20th century, the waste water from private individuals and industrialists was discharged directly into the waters of the Marseille coast, around the Prado area, more specifically into the “Calanque de Cortiou”. Marseille was one of the last coastal cities in France to have a wastewater treatment plant, which is why until 1975, the sea was polluted up to 47km off the coast. This pollution implied the disappearance of marine biodiversity, fish, corals, algae, everything  was gone.

In 1987, the treatment plant was set up, and many actions were undertaken to improve the quality of the water discharged into the sea. Although the quality of the water has clearly improved since these installations, nature still had great difficulty in regaining its rights, and marine biodiversity was still very low.

Hence the REXCOR project (Experimental Restoration of the shallow coastal waters of the CORtiou cove) was born, built from a proposal of ideas from different companies involved in biodiversity (EGIS, Architeuthis and CDC Biodiversity). The latter stipulated that the return of marine life would not occur as long as the substrate to be colonized would be of poor quality (because marked by many years of pollution), even if the water quality is very good. This is why they proposed to create new substrates on which life could once again be able to develop. Good substrate quality is essential for marine life. This substrate will condition the reproduction of species, allow animals and plants to grow, protect themselves from predators and weather phenomena, as well as to find food.

For this project, 10 million euros have been invested (6 million for the construction and installation of the reefs, 4 million for operating costs and the studies necessary for monitoring). The project has allowed 401 reefs to be submerged at a depth of 25 meters, with several shapes, in order to attract and shelter different species. They are located between the Corniche and the Friuli archipelago and are differentiated according to 3 types of morphology.

The 3 types of reefs installed :

• Fractal reef: Large concrete slabs placed at different levels, to recreate the conditions of a reef, its main function is the habitat of underwater species.
• Ragged reef: Superimposed concrete slabs, separated by a more or less wide space, allowing the habitat and reproduction of species.
• Connectivity reef: Mesh tubes filled with oyster shells and plant fibers, allowing juvenile species to take refuge there, as a kind of nursery.

 

In 2018, Marseille celebrated the 10th anniversary of the installation, with a rather positive balance sheet. In total, the number of fish species has tripled and the general marine biodiversity is growing. The results are very conclusive and are a source of hope both ecologically and socio-economically for lives that depends on the sea. Moreover, 10 years of monitoring are not sufficient to affirm the real effectiveness of the project. This is why a 4-year study will be set up to confirm this impression.