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The resilient coral reefs surviving ocean warming
Coral reefs are incredible ecosystems that support a quarter of all marine life. But these underwater habitats are under threat from coral beaching caused by ocean warming.
Museum scientists are studying bleaching-resistant reefs that may help sustain these vital marine environments.
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...
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 vital ocean habitats, such as coral reefs.
What are coral reefs?
Healthy coral reefs are teeming with life. © Andrea Izzotti/ Shutterstock
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.
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.
Corals are living colonies of polyps, tiny animals that secrete a hardened skeleton around themselves. This coral skeleton shows where the polyps lived when the coral was alive.
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
Reefs help to slow down waves and so protect coastal communities. © Edward Haylan/ Shutterstock
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.”
“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.
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.
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.
“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.”
“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?”
This stony brain coral specimen came from a healthy coastal reef that continues to thrive despite increasing ocean temperatures. Resilient species like this could be used to recolonise areas where bleaching has decimated other corals.
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.
