Congrès et conférences

Estaque T., Bianchimani O., Cheminée A., Garrabou J., Hartmann V., Sartoretto S., Schull Q., Mérigot B.

Marine heatwaves (MHWs) have been intensifying in frequency and magnitude, posing significant threats to marine biodiversity, particularly to sessile benthic species such as the red gorgonian, Paramuricea clavata. This study examines the status of P. clavata populations in the upper mesophotic zone (30 m – 60 m) of the French Mediterranean, a depth range that may offer partial refuge from MHW events. By analyzing data from more than 40 populations, we evaluate the health, density, and growth dynamics of these populations in the context of rising temperature anomalies and anthropogenic pressures. The findings provide insights into the vulnerability of mesophotic ecosystems and underscore the need for targeted conservation strategies in collaboration with Marine Protected Areas to mitigate the impacts of climate change on these critical habitats and support sustainable management initiatives.

Richaume, J., Estaque, T., Cheminée, A., Chemisky, B., Fargetton, M., Monfort, T., Drap, P., Bianchimani, O.

Photogrammetry, a technique to determine the shape, dimensions, and location of objects from multiple images, has been extensively used in marine environments for over 15 years. While one-camera photogrammetry is common, stereo-photogrammetry offers distinct advantages. To enhance 3D modeling and monitoring of marine habitats, we developed “KarKam,” a tool featuring two synchronized full-frame DSLR cameras on an aluminum platform with continuous lights and strobes, attached to a Suex xj37 underwater scooter.

This system accommodates various lenses, ensures exposure control, and automates photogrammetric image processing and calibrated scaling through scripted textured models. Using closed-circuit-rebreathers (CCR) divers and KarKam’s lighting autonomy enables coverage of approximately 500m² per session.

This study evaluates the effectiveness of stereo-photogrammetry for underwater 3D data acquisition, comparing it to traditional one-camera photogrammetry. To model the Liban wreck, one-camera photogrammetry captured 4,480 images with a ground resolution of 3mm/px over 15 sessions, while stereo-photogrammetry captured 26,588 images with a ground resolution of 0.547mm/px over 7 sessions. Stereo-photogrammetry provided continuous coverage and higher model reliability, though it is less practical for closed environments.

The second part of the study compared mono and stereo-photogrammetry for modeling and scaling accuracy on the Miquelon wreck (50m depth). Using Agisoft Metashape, three modalities were tested: left camera only, right camera only, and both cameras. Stereo-photogrammetry required 180 minutes of diving and 11 hours of modeling from over 20,000 pictures, providing better alignment and scaling accuracy with a mean error of 0.009m compared to 0.15m with one camera. Iterative Closest Point (ICP) comparisons highlighted the superior accuracy and robustness of the stereo model.

These findings underscore the importance of stereo-photogrammetry for high-precision underwater modeling. The KarKam system is an efficient tool for large area coverage with high chromatic quality, ensuring better accuracy with stereo scaling. A standardized approach would enable the comparison of quantitative data across different labs and stakeholders, enhancing marine ecology documentation and monitoring.

Gatti G., Barth L., Grancher T., Bastard–Bogain S., Blondeaux V., Bianchimani O., Estaque T., Monfort T., Richaume J., Cheminée A.

CIGESMED for divers is a citizen science program developed in 2016 by an international scientific team. It aimed to provide a scientifically–based simplified protocol for recreational divers to get involved in the monitoring of coralligenous reefs. Between 2016 and 2021, about 150 observations were collected by volunteer divers in and around the area of the Calanques National Park (Marseilles, France). The data collected allowed the qualitative and semi–quantitative description of the benthic communities of 27 diving sites and the assessment of some natural and anthropic pressures. Data were analysed by gathering observations over three consecutive years to get enough data to reduce the observer bias, and to allow temporal comparisons of the most frequented diving sites. It was then possible to characterise the abundance of the main taxa, as well as the pressures that occurred in this habitat. Their variation over time was also highlighted. Considering the limitations imposed by scuba diving to citizens’ involvement, as well as the lack of knowledge from recreational divers and diving instructors regarding coralligenous communities, those results were only made possible because of the enthusiastic coordination of a local network. Indeed, a diving and scientific organisation (Septentrion Environnement) proposed, every year, training sessions (theory and practice) and scheduled dives dedicated to CIGESMED for divers. By encouraging a feedback flow with the participants, it promoted the long–term involvement of citizens. CIGESMED for divers has proved to be an effective tool for the long–term monitoring of coralligenous reefs, particularly for local management purposes. It has also demonstrated to be a great tool for educational and training activities.

Dedet J., Bart L., Gatti G.

Le programme de sciences participatives CIGESMED for divers est dédié à l’observation de la biocénose coralligènes. Sur la période 2016-2018 des plongeurs volontaires ont collecté environ 80 observations au sein du Parc national des Calanques. Parmi les différents résultats issus de l’analyse des données collectées, nous avons présenté au Congres mondial de la Nature UICN un e-poster qui montre l’abondance et la distribution des espèces vulnérables / en danger et protégées, ainsi que de certaines pressions naturelles et anthropiques.

Berman L., Bianchimani O., Garrabou J., Drap, P., Payrot J., Accornero-Picon A., Clement A.-L., Cheminée A.

Dans le cadre de la gestion de deux AMP (le Parc National des Calanques récemment mis en place et l’AMP de Banyuls vieille de 30 ans) les populations de Corallium rubrum (Cnidaria) ont été étudiées afin de fournir aux gestionnaires des données utiles pour la gestion des populations. Des données sur la morphologie, le recrutement et la structure par taille de la population ont été collectées dans les deux AMP à l’aide de nouvelles méthodes photogrammétriques permettant des mesures tridimensionnelles précises. Nous avons évalué les structures de taille et la dynamique des populations et les avons liées aux niveaux de protection des deux AMP.

Cuadros-Casado I. A., Cheminée A., Vidal-Cejuela E. M., Thiriet P., Bianchimani O., Basthard-Bogain S., Francour P., Moranta, J.

We studied effects of depth and Cystoseira balearica forests canopy height on coastal juvenile fish assemblages of Minorca Island. Results showed a clear differentiation of juvenile fish assemblages due to depth: assemblage in the shallowest range (3-4 m) was characterized by higher densities of Thalassoma pavo, deeper ones (6-8, 10-12 m) by higher densities of Coris julis. Smallest juveniles of both species were more abundant within forests displaying the highest canopy height; meanwhile largest juveniles were more abundant within low Cystoseira forests. Also, both species showed predominantly a cryptic behavior on forest of higher canopy height, and a temporal one when canopy was lower. This study supports the importance of preserving healthy Cystoseira forests in order to preserve their nursery value for these two Labrid species