Corals are part of the cnidarian phylum, which means they are biological relatives of sea anemones and jellyfish. Corals are formed by a multitude of tiny genetically similar animals called polyps. These polyps are usually colonial, and able to produce a calcium carbonate skeleton that provides them with shelter and protection. Corals live in symbiosis with unicellular algae called zooxanthellae. These symbionts leave within the coral tissue, and are able to transform light energy into chemical energy and sugars (photosynthesis). Those sugars are directly transmitted to the coral host, and represents 80% of the coral nutritional input.
When corals face environmental stress such as an increase in the sea surface temperatures they start to eject their symbiotic zooxanthellae as they have started to over-photosynthesise and produce toxic levels of oxygen. This stress response, despite what it may seem, is actually a survival tactic for the coral. By reducing the number of zooxanthellae in their cells they reduce the amount of oxygen that is produced, however, by doing this the corals’ colouration is also removed, leaving them much paler than normal and sometimes completely white. It is at this point that we say the coral has bleached.
Despite their pale appearance, the loss of their algae does not explicitly mean they are dead. These stressed colonies are able to survive for up to a few weeks through active feeding mechanisms alone. During this time, corals are able to regain their algae should environmental conditions return to a manageable, stable level.
Coral Bleaching In The Maldives
Each year at the end of the ‘dry’ North East monsoon, the Maldives archipelago experiences an increase in sea surface temperatures and the effects of this can be observed on the coral reefs. Each year we expect to see some paling in color of the corals and even a little bleaching, with some colonies turning completely white. However, the sea surface temperatures during 2016 have reached a new high of approximately 34 °C. This unusually high temperature is due in part to the El Niño in the Pacific Ocean. The last major El Niño event was documented in 1998, which resulted in the approximate death of 95% of the coral in the Maldives. It is predicted that the event this year could cause as much damage, and maybe more.
Their Reefscapers Coral Reef Restoration program provides an opportunity to actively select fragments from coral colonies that are more resilient to the effects of temperature change. They have implemented to monitor of the bleaching on a weekly basis, and have already seen distinct variation in resilience between sites as well as species and frame age. Many frames like KH1124, located in our shallow Turtle site, have shown noticeable paling. Unfortunately conditions are expected to worsen in the near future, however, we hope that these species will recover in time.
It is important to recognize the significance of this fragile ecosystem and the part we play in these unprecedented variations in climate. Coral reefs are essential to the survival of thousands of species and without them we will see detrimental trends in species diversity and abundance, as well as consequential effects to tourism and fishing sectors that many countries like the Maldives rely on.