While the rate of artificalisation of the whole of the French Mediterranean coast is 12,27 %, wide differences are apparent from region to region:
- For the coast of Languedoc-Roussillon, the rate is 17,06 %,
- for the coast of Provence-Alpes-Côte d’Azur (not including Monaco and the Etang de Berre), the rate is 21,98 %,
- for the coast of Corsica, it is 2,68 %.
Within regions or counties (départements), distinct differences are also apparent:
- for the coast of the département of the Gard, the rate is 17,25 %,
- for the coast of the Alpes-Maritimes, it is 35,35 %,
- for the coast of the Bouches-du-Rhône (not including the Etang de Berre), 0,00 %,
- for the coast of the Principality of Monaco, it is 88,96 %,
- for the coast of the Etang de Berre, 42,02 %,
- for the coast of Corse du Sud, 2,47 %.
Apart from the impact on the landscape, the artificialisation of the coast represents an impact with regard to the qualitative and quantitative distribution or species which only live at sea level. The ecosystems situated at sea level (superficial part of the infralittoral zone and of the mediolittoral zone) are constituted of species possessing:
- high tolerance for variations in temperature (during periods of anticyclone the species are above the water level and thus tolerate over the year the terrestrial variations in temperature (-5 °C at the coldest point of the winter to +40 °C in the sun) with sudden changes when they are underwater– where the temperature ranges from 12.5 °C to 27.5 °C)
- high tolerance of variations in salinity (during anticyclones, the species are above the water level and thus tolerate considerable variations in salinity: from 0 (when it rains) to +50 ‰ when the species are out of the water and the sea water which soaks them evaporates.
This ensemble of species highly adapted to live in this narrow strip of coast is not found anywhere else (underwater, the species are not at all tolerant of variations in salinity or temperature). Thus their habitat is strictly limited to a frieze of 0.5 m to 3 m width along the coastline.
Among these species developing in this small space, there are the large brown algae (Stramenopiles of the genus Cystoseira) and calcareous red algae forming over time concretions (Rhodophytes of the genera Lithophyllum and Titanoderma). The species of this kind which constitute the main biomass at sea level (and therefore serve as support or shelter for other animal or plant species adapted to this environment) recolonise very poorly the artificial substrates (concrete, rock, etc.) The inventory of the distribution of the Cystoseires off the French Mediterranean coast shows that less than 0.5 % of the artificial coastline has been recolonised by species of this kind (Thibaut et al., 2008,2009,2010 et 2011).
The artificialisation of the coast thus engenders a local decline of the biodiversity (quantitative and qualitative) at very long term.

trottoir lithophyllum sur roches naturelles

Pavement of concretions formed by the red algae (Rhodophyte) Lithophyllum tortuosum on natural rocks. (Photo : A. Meinesz)

ceinture cystoseira sur roche naturelle

Belt of brown algae (Straménopiles) Cystoseira stricta var amentacea on natural rock. (Photo : A. Meinesz)

exemple littoral articicialise film cyanobacteries

Example of artificialised coast with only a film of brown Cyanobacteria visible on the rocks at sea level (Photo : A. Meinesz)