Tuesday, April 26, 2016

Coral Bleaching Basics & the 2016 El Nino

We have noticed the usual colours draining from our beautiful corals over the last few weeks. This phenomenon is known as Coral Bleaching, and is caused by excessive stressful conditions in the seawater. We have been collecting data to document this event, but before we share our findings, we wanted to help our readers to understand coral bleaching and why it is happening. To do this we must first understand what coral really is…

Tiny coral animals live together in colonies
Coral is made up of hundreds of tiny jelly-like creatures, all stuck together. Like a jellyfish, they have stinging tentacles that are used to catch plankton in the water for food. Their skin is see-through, but living within are thousands of plant or algal cells called zooxanthellae. Not only do these algal cells give the corals their colours (browns, greens and yellows), but they also provide the coral animals with lots of energy. In fact, about 90% of the energy that coral needs to survive is taken from these algal cells as they convert sunlight into sugars through photosynthesis. With this energy, the coral animals are able to build a hard, limestone skeleton by accumulating naturally occurring calcium and carbonate ions from the seawater. This skeleton is white, and this is what we see during coral bleaching events.

Some resistant or shaded corals evade bleaching...
...Others bleach bright white
The current bleaching is happening because of an increase in water temperature. We have all noticed the hot, calm weather recently. This is caused by El Nino- a weather phenomenon affecting the Pacific Ocean which is so influential that the whole world can feel the effects. Here in the Indian Ocean, we experience a rise in temperature. Since 1900, the world has endured 26 El Nino events, and this year’s El Nino is set to be the strongest in recorded history, with sea surface temperatures already rivaling that of the 1997/1998 El Nino, with an average increase of 2.3°C!

Acropora nasuta is almost fluorescent in a bleached state
The beautiful greens and purples are natural pigments usually
hidden by the zooxanthellae
These unusually high water temperatures are damaging the delicate relationship between the coral animal and algae, which live together symbiotically. The animal respires by taking in oxygen and releasing carbon dioxide as a waste product (just like humans), whereas the algae respires in the opposite fashion; by taking that carbon dioxide ‘waste’ and releasing oxygen. Thereby, the coral and algae use each other’s waste and live in a perfect balance. When the temperature increases, the algae start to release oxygen radicals, or bad oxygen molecules, which can damage animal tissues. Because of this, the animal must spit out what has become harmful algae. As the algal cells are ejected, the coral loses its colour. This coral is not dead, rather it is surviving in a stressed state, where it must try to gain all of its energy by capturing plankton. In this bleached state, without those energy making algal cells, coral can only survive for about 3 weeks, by which time the coral starts to metabolise its own tissues and, in effect, it starves. If the normal temperatures return, the corals can capture new algal cells for storage, recovering its colour and its vitality.

In 1998, the previous El Nino event was responsible for the loss of an estimated 80% of the coral in the Maldives! This current event is expected to be worse, where this hot weather will likely continue through until May. If this happens it could take between 10-15 years for many reefs to make any kind of recovery. El Nino events are increasing in severity and frequency- this is a direct cause of anthropogenic Climate Change. If the Maldives loses its reefs, it will lose its fisheries, its tourism and eventually its islands. These reefs are intrinsically linked to Maldivian survival- don't sit by and watch. Do your bit to help the planet. it is so important for us to try and reduce our carbon footprint, both as individuals and within our businesses! Help the planet and our coral reefs (and also your wallet) by saving energy, streaming for renewables, and reducing emissions!

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