A - Objectives

The objectives of this campaign were twofold: (1) Support for Public Policies regarding the MSFD and the measurement of habitat extent (Descriptor 6); (2) Research on population genetics.

The primary objective was to produce a high-resolution mapping of the reef-building coral populations Madrepora oculata and Desmophyllum pertusum (syn. Lophelia pertusa) in the Lacaze-Duthiers Canyon. Before this oceanographic cruise, the known distribution was based on observations made using the ROV Achille from Comex (Medseacan and Marum campaigns, 2009). These observations helped identify corals at the canyon head (Fabri et al., 2014; Fiala-Medioni et al., 2012). However, these dives did not allow for a comprehensive mapping of their population extent due to the camera's limited field of view. To achieve this, a systematic and exhaustive survey of the known sites in the Lacaze-Duthiers Canyon was necessary and technically feasible with the H-ROV Ariane.

The second objective of this campaign was to collect coral samples to analyze the connectivity between the Lacaze-Duthiers Canyon populations, that of the Cassidaigne Canyon, and those of the Atlantic, within the framework of the European H2020-ATLAS project (Arnaud-Haond et al., 2017; Becheler et al., 2017a; Becheler et al., 2017b; Dubois et al., 2016).

B - Expected Results

The analysis of video footage enabled the production of distribution and density maps for both coral species in the Lacaze-Duthiers canyon. These species form vulnerable marine ecosystems with fragmented habitats (Davies et al., 2017). These findings helped fill gaps in knowledge about deep-sea ecosystems, as highlighted by the MSFD, and provided valuable data for the European IDEM project (Implementation of the MSFD in the Deep Sea Mediterranean).

The results concerning population genetics contributed to the ATLAS project (European H2020 Project: A Trans-Atlantic Assessment and Deep-Water Ecosystem-Based Spatial Management Plan for Europe, 2016-2020). Although focused on Atlantic ecosystems, ATLAS included a significant data acquisition component aimed at understanding past and present connectivity (both oceanographic and biological) between the Atlantic and the Mediterranean, as well as its influence on species distribution across both ocean basins.

Additionally, the two reef-building coral species were part of the eDNAbyss project (France Génomique Grand Project), which included the sequencing of their genomes at Génoscope. Genome sequencing requires a large amount of DNA from a single individual (in this case, a single colony with no suspected anastomosis of fragments from different origins). Fresh tissue samples, specifically conditioned for this purpose, were collected for D.pertusum (syn. L. pertusa), a species for which existing collection samples did not meet the necessary quality or quantity standards. As a result, its genome was successfully sequenced in full.