Ecological status of the coral reefs of Reunion Island 2021-2023 - Activity report 3 - UTOPIAN
Etat écologique des récifs coralliens de La Réunion 2021-2023 - Rapport d'activité 3 - UTOPIAN
Abstract
The UTOPIAN project started in 2021. For the first year, UTOPIAN will be co-financed by the University of La Réunion and the BESTRUN association with LIFE4BEST funding. From 2022 to 2024, the project will be managed by the BESTRUN association with funding from IFRECOR (SOS Corail). UTOPIAN has three main objectives: (i) to map the state of health of coral reefs on Reunion Island, (ii) to understand the spatial distribution of state of health in the light of environmental pressures, and (iii) to provide decision support tools for public authorities to take greater account of coral reefs in territorial planning.
This progress report, which focuses on objective 1, highlights the fact that only 18% of the hard reef substrates of Reunion Island, from the shallow areas to 15 m depth, are covered by Scleractiniaria, with the genus Acropora accounting for 15% of the coral population. Comparing this result with data from the literature, it appears that there has been a loss of around 50% of coral cover over the last 40 years, a loss that has accelerated since 1998 as a result of increasing soil sealing and ongoing global changes. There are still some remnant areas, such as the outer slope of Grande Anse, which could serve as a reference state for Reunion's reefs in 2023, with a very well-structured coral cover of over 50%. The reefs of Trois Bassins and Saint-Pierre - Terre Sainte also contain some very fine remnants of plateaux with transverse orientations, anastomosing colonies and scattered elements, some of which show a tenacious capacity for resilience.
In the case of ichthyofauna, the densities of Scaridae and apical predators were estimated to be higher in the high protection zones (Zone de Protection Renforcée and Zone de Protection Intégrale) than in the zones outside the reserve. However, the beneficial effects of high protection zones are not limited to fish. In fact, independent of each other, reef complexes in high protection zones show on average better levels of structural integrity and vitality of their benthic populations, possibly due to more numerous and larger ichthyological populations (especially herbivores).