The loss of tropical corals reefs has become a symbol of the danger of climate change to the natural environment. These habitats are alive and vibrant, and may seem a world away form the cold streets of Glasgow, where world leaders gather for the UN climate summit.
Not far off the coast lie vast reefs made up of species of cold-water corals and calcified seaweed. This latter kind are commonly known as maerl beds and are created by a chalky pink seaweed filled with calcium carbonate – the same compound which makes up coral skeletons.
The UK’s western and northern sea shelves are surrounded by cold water coral reefs. They can be found at depths up to 50 metres. The UK is a European stronghold of maerl beds, especially in Scotland. They can be found all along Scotland’s west coast and around the islands.
Cold-water coral reefs or maerl bed, just like their tropical counterparts on the planet, are one of the most biodiverse ecosystems. They provide habitat for economically important species like pollack and scallops. catsharks. Sadly, despite their economic and ecological importance, climate change could erase Britain’s reefs by the end of the century.
Multiple threats are posed by climate change
Rising concentrations of carbon dioxide (CO₂) in the atmosphere are raising the planet’s temperature. The ocean has absorbed 93% excess heat since the 1970s. According to climate models, ocean temperatures could rise by more than 4°C by 2100As a consequence.
Each maerl species has evolved to thrive within a very limited temperature range. Many areas of the UK’s coastal seas are expected to become too warmFor native species, even after 2050
Scientists believe that cold water corals can withstand large temperature changes. They need to. raise their calorie intake to do so. Cold-water corals need more food to survive the effects of climate change and grow at a healthy pace. Corals are passive feeders. They use their tiny tentacles and snare any small animals, microscopic alga, or other debris that gets in their way. They will need to eat more food to weather climate change. However, they don’t have any control over it.
As the ice shelves begin to melt, fresh water is pumped into the ocean. This is expected to alter patterns of ocean circulation. The Gulf Stream – a warm ocean current which originates in the Gulf of Mexico – is already slower now than it has been for at least the past 1,000 years. This current influences the UK’s weather and climate, so any changes will have a big effect on the country’s coastal seas.
Cold-water corals are not like tropical corals that get energy from the sun. Instead, they get all their nutrition from plankton and other organic debris. The corals could be deprived of food if the currents change direction or slow down. Maerl beds can only be found where sediment is not smothered by fast currents. This allows maerl to make enough food through photosynthesis. Changes in water movement are expected to be a major factor in the loss of Scotland’s maerl beds over the coming decades.
Future for reefs
Greenhouse gas emissions don’t just heat the atmosphere. When CO₂ dissolves in seawater it makes it more acidic. The ocean is becoming more corrosive. plantsCalcium carbonate skeletons for animals. This is because cold-water corals are more sensitive than others to it, as they live in deeper waters with a pH that is already lower than the surface.
By 2100 more than 70%The waters that are corrosive for calcium carbonate are expected to be home to many cold-water coral habitats around the world. These conditions lead to weaker bones, similar to the loss of bone density in osteoporosis patients. Cold water coral reefs and maerl beds face a daily battering from animals, storms and dredging – weaker skeletons will make them more prone to damage, and may cause reefs to crumble.
For marine organisms, climate change can create multiple stress sources simultaneously. Both maerl and cold-water coral reefs will be unable to balance their energy budgets and build skeletons due to the combined effects. Both maerl (0.2mm/year for maerl), and cold water corals (0.2mm/year for maerl), grow very slowly and can live for hundreds of years. Some reefs are thousands years old. This means that their ability to recover from damage is much lower than those in faster-growing habitats like kelp forests. Loss of cold-water corals, maerl, and even a change in reef structuresThis will result in the loss of their homes for the animals and plants that live there.
The Scottish corals and maerl, from their watery vantage point would no doubt hope for positive outcomes in Glasgow. If greenhouse gas emissions do not stop, the North Atlantic’s cold-water coral reef habitat is likely to shrink. at least 79%By 2100 In the meantime up to 84%By the end of this century, the Scottish maerlbeds could be gone. But, if the global community can reduce emissions enough to limit warming to less than 2°C by 2100 (the maximum target in climate negotiations), the decline in Scottish maerl beds could be reduced to 38%.
Cold-water coral reefs and maerl beds are recognised as internationally-important habitats for biodiversity, and more recently for their potential to lock away lots of carbon. To avoid catastrophic losses in these habitats, the world must significantly curb greenhouse gas emissions and limit the effects of climate change – research suggests this will allow them to keep building their skeletons.
This story is part of The Conversation’s coverage on COP26, the Glasgow climate conference, by experts from around the world.
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