Coral Reefs in Seychelles Face New Dangers of Bleaching

Reprinted from the Save our Seas Foundation:

The islands of the Seychelles lie north of Madagascar in the Indian Ocean and are a mecca for tourists with stunning blue seas and palm fringed beaches. The islands and atolls, surrounded by fringing coral reefs, have also long been a strong attraction for thousands of divers every year, in particular those looking to encounter the endangered whale sharks and turtles. The area’s coral reefs, which support a large local fishing industry and were once claimed to be the most stunning in the Indian Ocean, were decimated by a coral bleaching event in the El Nino event of 1998, which damaged many reefs throughout the Indian Ocean.

Coral bleaching occurs when the tiny photosynthetic algae, called zooxanthellae, present within the coral polyp’s tissue leaves due to stress, such as that caused by an increase in water temperature. The zooxanthellae are essential for the survival of the coral as they provide each polyp with approximately 80% of its energy requirement. The exact mechanism via which corals bleach remains elusive, but it can result from a variety of factors (eg. changes in temperature or water chemistry) causing coral colonies to lose all colour and on most occasions starve to death. Soon, all that remains is a ghostly white skeleton.

Recovering coral in the Seychelles. Photo by Rainer von Brandis.

After the 1998 El Nino event the damaged coral in the Seychelles had severe knock-on effects for all marine life. What was once an area of pristine coral reefs transformed into expanses of barren rock and algae, much to the detriment of all organisms up the food chain. However, now more than a decade has passed and the marine life in the Seychelles seems to have been back on track for recovery; some stunning diving can be had similar tothat of the time before El Nino and many fish stocks have returned to healthy levels.

But, in recent weeks, there has been concern of further bleaching being caused by unseasonably high water temperatures…

SOSF cameraman Owen Bruce states ‘I spend a lot of time in the Seychelles. I love it here… it’s such a fascinatingly diverse place and I’ve had some incredible underwater encounters with all forms of marine life. One of the highlights for me is always returning to familiar dive sites and checking up on the development of new young coral colonies that in the last two years in particular have started to do really well. In the last month or two though the water has been noticeably warmer (a local dive guide told me the water temperature reached 31 degrees celsius in March) and the number of newly bleached coral colonies is quite alarming. The glowing skeletons are visible below as soon as you get into the water.‘

Even without the threat of coral bleaching, the Seychelles is an archipelago subject to various pressures on the marine environment such as unsustainable over fishing practices, including shark finning by local and foreign vessels and the harvesting of numerous marine species from shells and sea cucumbers to hawksbill turtles. The recent bleaching of coral, and the concern that 2010 may prove another El Nino year, is worrisome to those who fear that another large bleaching event may be disastrous for the marine life of the Seychelles and all who depend on it for their livelihoods.

Recent bleaching on a reef in the Seychelles. Photo by Rainer von Brandis.

Leader of the SOSF hawksbill turtle project in the Seychelles added ‘The bleaching was indeed quite bad this year. Here at D’Arros it was certainly the worst year since the 1998 event. I estimate that in excess of 50% of the remaining corals of the genus Poccillopora alone have perished. The entire month of April was calm with very clear water and this led to an extended period of high sea surface temperatures. Often coral polyps can survive short periods of bleaching but now that the temperature has reduced again (27 degrees at present), it is evident that most have died.‘

Further coral bleaching will affect all forms of marine life in the Seychelles, some in more direct ways than others. It will damage the foraging ground of endangered hawksbill turtles, affect the plankton on which the whale sharks come to feed and will disrupt local fisheries by removing a resource on which so many fish species depend.

Increasing frequency of severe bleaching events around the world is of growing concern in the current context of ongoing climate change.