We monitor the health of the coral reefs around D’Arros Island and St Joseph Atoll using various indicators, including ambient environmental parameters, benthic cover and composition, coral recruitment and coral bleaching events. Data collected from our long-term monitoring of reef fish communities are also incorporated as an indicator of reef health. The work to acquire this data is extensive, including a lot of dive surveys, photo analysis and environmental monitoring. Our staff take about one month of every year to fulfil all field-work requirements.
The aim of this project is to assess trends in the health of coral reefs at D’Arros Island and St Joseph Atoll.
The dynamics of coral reef ecosystems are complex and varied, with many different processes interacting. There is a need to monitor reef dynamics and health over the long term to better understand their function and the causes of bleaching events, as well as the ability of reefs to recover from them.
Coral reefs form the basis of some of the most diverse marine ecosystems in the world. Despite only occupying 0.1% of the world’s ocean area, they provide a home for about a quarter of all marine species at some point in their lives. In terms of their value to us, coral reefs are a huge food and tourism resource that supports millions of livelihoods. They absorb energy from waves and contribute to environmental protection by reducing coastal erosion.
Research has shown the widespread destruction of reefs in recent decades and the associated population declines of reef-dependent marine species. One third of reef-building corals are currently on a trajectory to extinction. Coral reef bleaching is a major component of this destruction and occurs when corals expel symbiotic organisms called zooxanthellae. This expulsion is a stress response by corals that is most often brought about by increases in water temperature that, due to global climate change, are occurring more frequently and for longer periods.
In the face of ever-growing threats to reef systems, dedicated and long-term research can uncover patterns in coral reef health and disturbance regimes.
The key objective of this project is summarised in four sub-objectives that each address different indicators of coral reef health:
To supplement much of the research conducted on site (e.g. coral monitoring and reef fish surveys) and to help better understand the lives of the animals using D’Arros Island and St Joseph Atoll, it is important to measure and monitor environmental conditions. One of the most important of these is sea temperature. A series of small loggers deployed at different areas and depths around the islands constantly record the water temperature. Additionally, via our on-site weather station, we collect meteorological data every day, including on wind, rainfall and air temperature.
D’Arros Island and St Joseph Atoll have been identified as one of the most important areas in Seychelles and the broader Western Indian Ocean for hawksbill Eretmochelys imbricata and green Chelonia mydas turtles, with both species using the beaches for nesting. We continually monitor their presence at the islands, collecting data both from individual animals present on the beaches and from the tracks they leave behind. From these we can estimate the population sizes and growth of these two turtle species.
A large population of reef manta rays Mobula alfredi occupies the near-shore waters of D’Arros Island. Each of these rays has unique markings on its ventral surface (belly) that enable us to identify different individuals. From this we gather information about how many mantas are using the site, where they spend their time and for how long. We use various photograph and video techniques to identify manta rays at D’Arros, including the deployment of cameras at a regularly visited cleaning station. Working with the Manta Trust, we incorporate our data into a broader regional understanding of the population and ecology of these threatened animals in Seychelles.