Kerry MacKay sets out the causes and ongoing impacts of coral bleaching, and what we all can do to mitigate the contributing factors
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ENVIRONMENT
Losing colour
Kerry MacKay sets out the causes and ongoing impacts of coral bleaching, and what we all can do to mitigate the contributing factors
Most of us think the impacts of climate change are something that will happen in the future. Just as most of us think of the 90s as being“ not that long ago”( psst, that was 30 years ago!).
Perhaps the increase in storms and heat waves is the most noticeable change topside. We divers stand a better chance of noticing impacts in the seas compared to other people, and perhaps the easiest to spot is coral bleaching.
Coral is famous for many reasons. It’ s beautiful; it’ s home and a nursery to other species; it provides food for people and creatures, and is perhaps best known as many divers’ dream holiday destination.
Coral is also famous in scientific circles. It is what is called a‘ Keystone’ species( granted, there are many species of corals). This means they are one of the most important species in a particular ecosystem, and without them, that whole ecosystem would crumble.
It is a symbiotic organism that lives in partnership with brightly coloured algae called zooxanthellae. The coral provides a safe place for the algae to live within its tissue. In return, the algae
photosynthesise and give the coral food.
Corals bleach when they are stressed, which can be due to pollution, too much sunlight, and / or temperature changes. In fact, a change of just 1-2 ° C above the normal summer maximum can trigger bleaching!
When the coral and zooxanthellae get stressed, the zooxanthellae create harmful chemicals, so the coral expels them. This leaves the coral appearing white or pale due to the colour of its calcium carbonate skeleton.
Coral can survive a bleaching event if it is short and not too severe. Once conditions return to a tolerable range, the zooxanthellae can re-colonise the coral, returning it to its familiar colours in a few weeks. However, it can take the coral years to fully recover. This leads to poorer overall health of the reef and makes them much more vulnerable to future bleaching events.
The Paris Agreement, signed in 2015, set the target of limiting global warming to no more than 1.5oC rise above preindustrial levels by 2100. This is the level of climate change that scientists predicted will be manageable for humanity. However, our average global temperature has already risen by 1.3 ° C above pre-industrial levels. The ocean’ s surface layer( top 700 metres) has warmed by 0.9 ° C on average. In May of both 2024 and 2025, we saw record-breaking marine heatwaves in the UK. The entire west coast of the UK was 2.5 ° C above average this spring. Just off Tyne and Tees, temperatures were 5 ° C higher than average.
The ongoing global coral bleaching event, which began in 2023, is the worst yet. Heat stress has impacted 83.9 % of the world’ s coral reefs. In the southern Great Barrier Reef in 2024, certain types of coral, such as Acropora, had a staggering 95 % mortality rate.
Scientists estimate we could lose 70-90 % of coral reefs by 2045 due to bleaching and other warming impacts.
This is such a complex global issue that I cannot give you one simple action that will xxxxxxxxxxxxxxxxxxxxxxx
save coral. But, I can give you one simple action to dramatically reduce your personal impact on the climate, which will help coral.
Electricity generation is the single biggest source of greenhouse gases. Switch your electricity provider to a 100 % renewable tariff. Get your workplace and community buildings to switch too. Ecotricity, 100Green, and Octopus Energy are all highly rated for their‘ green’ efforts. Switch today to enjoy coral dive holidays in the future. �
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