You don’t have to be a scientist to have heard about coral bleaching. Over the past 50 years, this topic has gained growing attention from both the media and ocean lovers. But do you know what coral bleaching is and what causes it? Let’s delve into it!
What is coral bleaching?
Coral bleaching is a stress response of corals that results in the loss of their primary source of food and colour. Corals live in symbiosis with tiny algae called zooxanthellae, that they host in their skin. These microalgae are responsible for the bright colourations of corals. Moreover, they provide corals with 90% of their energy intake. Under certain environmental conditions, this symbiotic relationship ends, and the corals expel the zooxanthellae, turning white.
What triggers coral bleaching?
Coral bleaching can be triggered by multiple factors such as extremes of temperatures, pollution and pathogens. However, the recent large-scale bleaching events have been attributed mainly to increased seawater temperature linked to climate change.
What happens after bleaching?
A bleached coral is not dead, or at least not yet. A coral can survive in this state for a few weeks. If the environmental conditions that triggered coral bleaching return to normal, corals can regain their symbiotic algae (and colour) and survive. However, prolonged warmer water temperatures will ultimately lead to the death of the bleached corals.
Coral bleaching in the Maldives.
We talk about mass coral bleaching when the area affected by this phenomenon spans several kilometres. In the Maldives there have been two major mass bleaching events, in 1998 and 2016, and two minor ones in 2003 and 2010. Maldivian reefs have been severely affected by these events, which are increasing in frequency and intensity. After the major bleaching event in 2016, the national coral cover declined rapidly, reaching the second-lowest percentage ever recorded in the country. However, coral cover appears to be increasing since then.