In December, 36 artificial reefs will be installed across multiple sites in the cove of Cortiou in Marseille. This operation, called REXCOR (Experimental Ecological Restoration of the shallow marine environment of the Calanque of CORtiou), is intended to be experimental. The modules, specially created for the occasion, aim to bring back marine life to this now barren cove.
Situated at the outlet of the city’s wastewater, the Calanque of Cortiou had been polluted by Marseille’s discharges from the 19th century until the 1980s. Following the installation of a wastewater treatment plant capable of processing 325,000 m3 of polluted effluents per day, and recent sanitation works, the water quality seems to have returned to an acceptable level. “Today, the waters of Cortiou are of good quality and the conditions are in place to implement this project and bring back marine life,” explains Didier Réault, chairman of the board of directors of the Calanques National Park. This artificial reef project is supported not only by the Park, but also financially by the Water Agency Rhône Méditerranée Corse and by the Pôle Mer Méditerranée.
Three modules for three distinct functions
Following a call for ideas, the innovative artificial reefs project by the Egis group – in association with CDC Biodiversity and Architeuthis – was selected: three types of modules were specially crafted for this project. Depending on their shape and location of installation, each will have a very specific purpose.
- – The fractal reef: formed of large concrete petals, placed at different levels and exposures, its aim is to recreate the conditions of a reef. With parts more or less protected from currents or light, it should facilitate the establishment of various species. In theory, its main function would therefore be the habitat of marine species.
- – The cave reef: composed of superimposed concrete slabs, separated from each other by more or less significant gaps, it allows for the installation of species that appreciate rocky crevices. Corbs, sea breams, groupers, or lobsters should appreciate this reef facilitating their shelter. This reef is intended as a habitat but could possibly serve as a breeding site.
- – The connectivity reef: made with long mesh tubes filled with oyster shells and plant fibers, it offers numerous spaces for juveniles to shelter. Located in shallow coastal waters, its primary purpose is to serve as a nursery for different species (groupers, sea breams, wrasses, comber fish, scorpionfish…).
Regular monitoring for three years
The modules will be placed between 100 and 1,500 meters from the discharge of the treatment plant, across four distinct sites. This being an experimental operation, there is no certainty regarding its effectiveness in bringing marine life back to the Calanque of Cortiou. Furthermore, the usefulness of the experimental modules, with their innovative shapes, is not guaranteed. The next three years will be critical: monitoring will be conducted on the sites to observe the development of the reefs, in the hope of seeing them colonized. In the event of this trial’s success, a larger-scale operation could be considered to restore the entire seabed of the Calanque of Cortiou.
The installation of the modules is expected to take place in the coming days, and we will update this article once it is done.
Margot Harty