Faunal and Floral diversity ofhard substrate from the CHERLOC experimental dike

Aurore Raoux (1) , Mael Deloor (2) , Mathilde Charbonnelle (1) , Pascal Claquin (2) , Robin Van Paemelen (1) , Etienne Cunge (3) , Lise Delatte (1) , Jean-Claude Dauvin (1) , Dominique Mouazé (1) , Anne-Marie Rusig (2) , Isabelle Mussio (2) , Jean-Philippe Pezy (1)

1 M2C - Morphodynamique Continentale et Côtière
2 BOREA - Biologie des Organismes et Ecosystèmes Aquatiques
3 Artelia Eau & Environnement [Echirolles]

More than 60% of the world's population live within 150 km of the coasts. Natural shorelines are therefore very arti cialized and sometimes lose their role as bu er zones. Moreover, the context of global warming is leading to a rise in the sea level and a potential change in the intensity and frequency of storms, implying a need for reinforcement of coastal defense in some place. In this context the main objective of the CHERLOC engineering project is to study on two pilot sites in Normandy two new types of arti cial blocks integrated existing dikes. CHERLOC support a multidisciplinary approach, which seek to assess their interest in coastal engineering, but also on marine biodiversity and social acceptability. The ecological study carries out an inventory of the benthic diversity (flora and fauna) recorded on both sites (Ouistreham and Cherbourg) before the blocks implantation during four sampling campaigns conducted on the hard substratum of the mediolittoral. The collected samples were sorted and analyzed in the laboratory. In addition, every quarter a monitoring of the artificial blocks was made at each site and thus during two years. For the fauna, there is a dominance of the barnacle crustaceans Semibalanus balanoides which represents 80% of the individuals sampled on all the stations of the two sites. Moreover, at Ouistreham a second species the bivalve mollusk Mytilus edulis represents 17% of the total. Although due to the dominance of these two species the diversity index is low, the ecological status of both sites is classi ed as very good. For the flora, Fucoid species (Fucus spiralis, F. serratus and F.vesiculous) dominate the upper parts of each site. The lower part of the site outside the Cherbourg harbour and the Ouistreham site are devoid of algae. The lower part of the site inside the large Cherbourg roadstead is dominated by an assemblage of gigartinales; Chondrus crispus and Mastocarpus stellatus with respectively 2% for both in October then 20% and 3% in March. The qualitative state from a macroalgal point of view of the sites at Ouistreham, outside the large Cherbourg harbour and inside the large Cherbourg harbour are respectively Poor (36/100), Average (51/100) and Good (70/100). According to the EUNIS typology, the faunal and floral assemblages made it possible to classifies the study areas, the sites of corresponds to a marine intertidal rock habitat under strong hydrodynamics with a biocenosis with mussels and/or barnacles (A1.11). Ouistreham lower mediolittoral sampled in October corresponds to the sub-level A1.111 habitat and the upper, medium and lower mediolittoral sampled in March at the sub-level habitat A1.112. At Cherbourg the distinction between the two sub-habitats is clearer; the lower mediolittoral corresponds to the sub-habitat habitat A1.1131 and the upper to the sub-habitat A1.1133. Taxonomic Richness and abundance show high seasonal changes at both sites with minima in winter and maxima at the end of the summer. The authors thank Normandy Region and the FEDER for co-funding the collaborative CHERLOC project. They also thank Ports de Normandie for their assistance during the project.

Domains: Environmental Sciences; Biodiversity and Ecology

Aurore Raoux, Mael Deloor, Mathilde Charbonnelle, Pascal Claquin, Robin Van Paemelen, et al.. Faunal and Floral diversity ofhard substrate from the CHERLOC experimental dike. Premières Rencontre de l'Ingénierie Maritime, Jun 2022, Caen, France. ⟨hal-03853356⟩