Background: A strong behavioural plasticity is commonly evidenced in the movements of marine megafauna species, and it might be related to an adaptation to local conditions of the habitat. One way to investigate such behavioural plasticity is to satellite track a large number of individuals from contrasting foraging grounds, but despite recent advances in satellite telemetry techniques, such studies are still very limited in sea turtles.Methods: From 2010 to 2018, 49 juvenile green turtles were satellite tracked from five contrasting feeding grounds located in the South-West Indian Ocean in order to (1) assess the diel patterns in their movements, (2) investigate the inter-individual and inter-site variability, and (3) explore the drivers of their daily movements using both static (habitat type and bathymetry) and dynamic variables (daily and tidal cycles). Results: Despite similarities observed in four feeding grounds (a diel pattern with a decreased distance to shore and smaller home ranges at night), contrasted habitats (e.g. mangrove, reef flat, fore-reef, terrace) associated with different resources (coral, seagrass, algae) were used in each island. Conclusions: Juvenile green turtles in the South-West Indian Ocean show different responses to contrasting environmental conditions -both natural (habitat type and tidal cycle) and anthropogenic (urbanised vs. uninhabited island) demonstrating the ability to adapt to modification of habitat.

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Ocean warming is increasing the incidence, scale, and severity of global-scale coral bleaching and mortality, culminating in the third global coral bleaching event that occurred during record marine heatwaves of 2014-2017. While local effects of these events have been widely reported, the global implications remain unknown. Analysis of 15,066 reef surveys during 2014-2017 revealed that 80% of surveyed reefs experienced significant coral bleaching and 35% experienced significant coral mortality. The global extent of significant coral bleaching and mortality was assessed by extrapolating results from reef surveys using comprehensive remote-sensing data of regional heat stress. This model predicted that 51% of the world’s coral reefs suffered significant bleaching and 15% significant mortality, surpassing damage from any prior global bleaching event. These observations demonstrate that global warming’s widespread damage to coral reefs is accelerating and underscores the threat anthropogenic climate change poses for the irreversible transformation of these essential ecosystems.

Monitoring and health state 2007 of coral reefs of Mayotte Island.— The principal characteristics of Mayotte Island are the length of the reef-barriers delimiting one of the widest lagoon of the area, a double reef-barrier (uncommon geological structure) as well as a general dynamics being equivalent to that of a series of eight reef-lagoon complex being able to function independently. Specifi cities of the environmental parameters combined with the particular characteristics generate a singular dynamics of the ecosystem and addicted communities. The objective of the Observatory of the Coral Reefs of Mayotte is to ensure, on the long term, the acquisition of reference data on the coral ecosystems of the island in order to evaluate the spatio-temporal evolution of the benthic and ichtyologic communities, this associated with more specifi c objectives (will ciguatera, whitening, SIG, coordination and management). To succeed in doing that, regular surveys are carried out (station of reference ORC, fringing reef, Reef Check), associated with specifi c studies and initial states. More than 9 years after the phenomenon of massive whitening, the results of the ORC show a continuous and encouraging evolution of the coral growth. However, the dynamics of substrate recolonization by new individuals varies according to the three types of reefs present.

Coral reefs of Réunion Island in 2007 : status report and monitoring network.— Réunion Island is 2500 km2 and belongs to the outermost regions of European Union (EU). The population attained 774 600 inhabitants in 2004 with 25 % living in the western part of the island, 80 % in the littoral zone (called «bas»). The gross domestic product (GDP) per capita is less than 50 % of the mean index of the EU. The rate of unemployment was of 33 % in 2004. Coral reef ecosystems extend over 12 km2 along 25 km of the west and south coasts of the island. In addition to the natural infl uence of climatic events (global change) coral reef ecosystems are impacted by direct and indirect influences of the increase of human population. Direct impacts are mainly due to human overfrequenting of reef flats and overfishing. Indirect impacts are due to urbanization and to industrial, agricultural and urban pollutions. The competence in marine environment is assumed by an administration (Direction Régionale de l’Environnement). Researches on coral reefs are run by research institutes and NGO. The first coral reef monitoring network was set up in 1998 on the Saint-Gilles/La Saline reef. Since then, it was extended to the three other main reef units (Saint-Leu, Étang-Salé, Saint-Pierre) and the data are gathered since 2001 by ecoguards of the association «Parc Marin de la Réunion», with the partnership of the university (Laboratoire d’Ecologie Marine). Data are stored in a database (COREMO) and analysed by ARVAM (Agence pour la Recherche et la Valorisation Marine). The operation is funded both by the state administration and a local administration (Conseil Régional). Réunion Island is a part of the South-West Indian Ocean node of the Global Coral Reef Monitoring Network (GCRMN). It is regularly involved in the writing of the «Status of coral reefs of the world». At the same time another network involving stakeholders is built using the Reef Chek protocole. At the present time, coral reefs of Réunion Island are deteriorated. If the density of the targeted species of fi sh has not changed since 1999, the surface of live corals has shown a significant decrease on half of the 14 stations, particularly after two bleaching events in 2003 and 2004. The various negative impacts due to human activities contribute to weaken these ecosystems and to decrease their resilience. Hence, they are less and less able to resist exceptional climatic events (hurricanes, swells) and the bad impacts of global change (bleaching). To face to the stake of long term development, 75 % of the reef units of the island are protected since February 2007 by the status of «Réserve Naturelle Nationale Marine» (35 km2 of marine protected area).