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Climate Conversations: The Rainforests of the Ocean

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Our Climate Conversations series continues with a look at how the current climate is affecting the ocean. 

Vital to our oceans, corals are highly threatened by humans. Climate change means that warm water corals are at very high risk of severe damage by the end of the century. But is all hope lost? Can we save our corals?

Coral reef in the Red Sea at Eilat, Israel, Daviddarom/Public domain

The Rainforests of the Ocean

Coral reefs have been described as the ‘rainforests of the oceans’. Like the rainforest, reefs are full of life, yet they manage to thrive on very little. Full of colour and movement, reefs are home to around a quarter of marine life. They are important places for fish to feed and breed. Crabs, sea slugs and other molluscs shelter in their rocky architecture.

What are corals?

Corals may look like stony outcrops, but in fact they are alive. Small animals called polyps produce a chalk-like substance (calcium carbonate) which forms the reef around them. The polyps use tentacles to catch food from the water. Algae (simple plants) live alongside the polyps and help them to harvest food. Where the sea is shallow, light passes through the water and stimulates the algae, making the reef highly productive. The algae are also responsible for giving corals their colour.

Where can we find corals?

Corals occur in warm tropical waters where the temperature is between 18 and 30oC. For example, the Great Barrier Reef runs for 1600 miles along the north-eastern coast of Australia. Corals are also found in the Red Sea, Indian Ocean, East Africa and around the Caribbean, Mexico and Florida.

Corals in the UK?

In contrast to the warm water reefs, cold water corals grow slowly in the deeper, darker waters off north and west Scotland, the west of Ireland and the south-west coast of England. Cold water corals can be found as far north as Alaska. Fishing boats dragging equipment along the sea-bed (known as trawling) can smash coral to pieces and so has been banned in some of these areas.

What does climate change mean for coral?

A scientist studies corals in the Virgin Islands National Park, photo: NS CC BY 2.0

Climate change is a major threat to corals. This is because it poses two very significant risks: rising temperatures and ocean acidification, both of which can cause coral reefs to weaken and die.

Rising temperatures

High temperatures are a major cause of coral bleaching. Coral bleaching is when the coral loses its colour and turns white. Corals are usually bright and colourful because of the algae that lives inside it’s body. When temperatures rise, it causes stress to the coral which makes it expel the algae. The corals that are bleached can recover, but if temperatures stay high enough for a long time they may eventually starve and die.

Bleached coral. Elapied at French Wikipedia.CC BY-SA 2.0 FR

Coral skeleton from the Booth Museum of Natural History

Bleaching can happen when the water temperature is 1oC above its normal maximum. Such high temperatures are likely to be more common, more extreme and longer lasting as a result of climate change. Several global-scale bleaching events have already happened, including one in 2016 which damaged large stretches of the Great Barrier Reef.

If temperatures rise by 1.5 oC as a result of climate change, warm water corals will be at very high risk of severe and irreversible damage. Currently, we are on course for temperatures to increase by nearly double that amount. Even if countries around the world meet their current pledges under the Paris Agreement on climate change, then temperatures could be 2.8 oC higher by 2100.

It’s not just climate change…

Corals are also threatened by over-fishing and fishing in damaging ways including trawling and dynamiting reefs. Tourism and shipping cause problems for reefs if they are badly managed. For example, if people collect or damage coral, if sun-screen gets into the water, or if boats pump oil and waste into the sea.

Urgent action is needed!

Countries around the world have been taking steps to protect reefs from fishing, pollution and other types of damage. This includes setting up marine protected areas (also known as marine conservation zones). These are parts of the sea where damaging activities are either limited or banned altogether. International bodies have called for 30% of the sea to be protected globally, although only around 2.5% to 5% is well protected currently.

Find out about the UK and Sussex’s Marine Conservation Zones.

What can I do?

  • As a consumer, you can choose to eat fish and sea-food that has been caught in a sustainable way and to avoid fish (such as the orange roughy) that comes from cold-water coral reefs.
  •  Avoiding sun-screen containing oxybenzone.

While these measures will help, coral reefs will be in danger unless major steps are taken to cut back the fossil fuels that cause climate change.

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Diana Wilkins, former Climate Scientist and Booth Museum volunteer