Coral reefs at risk
These vital ecosystems are under threat, but some are surviving the warming waters
The Natural History Museum
By Roween Rawat
A clearwater reef by Nadia SantodomingoThe Natural History Museum
Covering 70% of the planet, the ocean consists of all sorts of habitats teeming with life. It provides half a billion people around the world with food and income and it’s also our protector...
Snorkelers in the Great Barrier Reef (2020) by Phil WarringOriginal Source: Tourism Australia Image Gallery
The ocean has absorbed 90% of the global warming that has occurred in recent decades due to our fossil fuel burning. This has shielded us from unsurvivable temperature increases, but at a cost to ocean habitats, such as coral reefs.
Australian corals by Nadia SantodomingoThe Natural History Museum
What are coral reefs?
Coral reefs are incredible ecosystems. Despite covering just 0.1% of the ocean floor they support 25% of all marine life.
‘Corals are made up of colonies of tiny animals called polyps that are related to jellyfish,’ adds Natural History Museum coral scientist Ken Johnson.
A close-up of a coral skeletonThe Natural History Museum
Microscopic algae live within these polyps. Through photosynthesis, they supply the coral with food and in return receive nutrients and shelter. But this relationship is fragile. ‘When ocean temperatures get too warm, this relationship breaks down,’ notes Ken.
What’s harming coral reefs?
When the algae are ejected from the polyps, the coral’s white skeleton is revealed. This is called coral bleaching. Without algae present, corals starve.
Marine heatwaves are becoming hotter and more frequent, so bleaching is happening more often. But that’s not all.
Other threats include:
- overfishing animals that graze on marine algae, leading to it smothering reefs
- lethal diseases such as stony coral tissue loss disease
- water pollution, leading to algal blooms that stop sunlight reaching corals, preventing photosynthesis
A selection of fossil corals from IndonesiaThe Natural History Museum
Rising oceans might also pose a threat to reefs, but ‘if corals are healthy, they can grow as fast as sea levels rise,’ says Ken. ‘In the fossil record, we can see that they managed to keep up with the ocean rise due to glacial melt over the past 2.6 million years.’
Coral skeletonThe Natural History Museum
‘Reefs build up through depositing calcium-carbonate skeletons, essentially building limestone walls,’ he expands. These walls break incoming waves and protect coastal communities from storm surges and tsunamis. Without this, these communities will be left vulnerable.
Why are coral reefs important?
Why are coral reefs so important?The Natural History Museum
Acropora millepora coralThe Natural History Museum
Resilient reefs of the future
While conservation teams around the world are working hard on regrowing corals to restore reefs, another potential solution might come from looking at the corals that aren’t struggling in warming seas.
Elkhorn coral, Acropora palmataThe Natural History Museum
Ken’s team are studying reefs that grow in cloudy waters and seem to be more resistant to bleaching events. The team think this may be the result of intense light accelerating bleaching, so corals that grow in lower light conditions, such as murky or deeper water, are protected.
Stony brain coral, Oulophyllia speciesThe Natural History Museum
‘Reefs that live in this middle-light range don’t seem to bleach like their clearwater counterparts,’ shares Ken. ‘Worldwide, we need to identify the reefs that are likely to survive, document them and identify the most resilient species.’
Brain coralThe Natural History Museum
‘They’re not as pretty as clearwater reefs, so often go overlooked. But these turbid reefs might be the ones to survive climate change,’ adds Ken.
‘We’re investigating if clearwater reefs die, could they be repopulated by turbid reefs?’
These overlooked reefs may hold the key to sustaining coral reef habitats, but we must also tackle the main cause of bleaching: higher ocean temperatures.
We need to limit our greenhouse gas emissions to prevent further warming to give coral reefs the best chance of survival.
