Coral can tell us a lot about the environment it is found in, particularly if that environment is changing for the worse. Based at D’Arros Island and St Joseph Atoll in the Amirantes Islands of the Seychelles, Kerryn Bullock describes some of the ways in which researchers are monitoring local reefs.
Coral reefs are considered to be the most biodiverse ecosystems on earth, home to a multitude of different types of fish, invertebrates and turtles. They cover less than 1% of the sea floor, yet support an estimated 25% of all marine life. As well as providing feeding, refuge, spawning and nursery areas for a large variety of organisms, reefs are natural breakwaters that minimise the impact of waves from storms.
Defined as a marine polyp with a calcareous skeleton that lives in colonies, hard coral provides a prime example of symbiosis: sym meaning ‘together’ and biosis meaning ‘life’ – in other words, organisms living together. It also illustrates mutualistic symbiosis, as each organism in the union benefits from the presence of the other. The two organisms in question that live inside the skeleton of the coral colony are coral polyps and colourful, one-celled algae called zooxanthellae. The algae produce oxygen and nutrients through photosynthesis and these are used by the coral polyps. In return, the coral polyps produce carbon dioxide and calcium carbonate, which the algae need to thrive. The polyps then use the calcium carbonate to build a cup-shaped skeleton structure that is strong enough to withstand typical wave action. Coral grows only where the water is shallow enough for the sun to penetrate, enabling the algae to photosynthesise.
Sudden changes in water temperature can have a profound effect on coral reef ecosystems. In 1998 almost 70% of hard corals in the Seychelles region perished due to the uncharacteristically warm sea water. Coral bleaching occurs when above-average sea temperatures result in the expulsion of the zooxanthellae. The loss of these photosynthetic algae turns corals white, diminishes their energy resources and eventually results in their death. Therefore, given today’s changing climate and predicted coral bleaching, it is of utmost importance to monitor the temperature of the sea surface and to integrate the resulting data into surveys of coral health.
A biological field station based on D’Arros Island in the Amirantes Group, Seychelles, the SOSF D’Arros Research Centre (SOSF–DRC) conducts research on the pristine D’Arros Island and St Joseph Atoll and the waters around them. In recognition of the islands’ outstanding natural values, the research centre was established in 2004 and tasked with becoming a regional centre of excellence for marine and tropical island conservation. Initially, collaborations were established with local and international institutions and baseline ecological surveys were conducted in the various habitats. Over the ensuing years an increasing number of research projects and monitoring programmes were implemented in response to questions raised by the baseline surveys and by visiting scientists. More recently, the centre expanded its activities to include ecosystem restoration and environmental education.
Today the SOSF–DRC boasts the longest-running nesting turtle monitoring programme in the Amirantes and the most detailed and technically advanced coral reef monitoring programme in the Seychelles, making use of techniques such as stereo-video photogrammetry, photoquadrats, remote underwater video systems (BRUVs) and visual census. The research centre also maintains the largest acoustic receiver array in the Seychelles, which monitors the local movements of sharks, manta rays, stingrays, turtles and fish. Since its inception in 2004, the centre has initiated no fewer than 36 research projects in collaboration with more than 26 conservation institutions. The projects have resulted in 10 peer-reviewed scientific papers, one PhD and one MSc dissertation, five conference presentations and 27 scientific reports.