THE TRIPLE PLANETARY CRISIS
Shallow-water coral bank in Chilean fjords, photo credit: Vreni Häussermann & G. Försterra
Cold- or deep-water corals build and maintain an ecosystem where the water is icy cold and the light dim or absent.
These corals and gorgonians are so-called ecosystem engineers, the 3-dimensional structures they build are called marine animal forests. Here many invertebrates find habitat, protection and food.
In the depths of the ocean, where the water is frigid and light barely penetrates, lies an unexpected wonderland of corals. Surprisingly, vibrant coral gardens thrive in these extreme conditions, reaching depths of up to 6,000 meters. Contrary to popular belief, the majority of coral reefs aren’t nestled in tropical shallows but rather in the deeper, colder realms of the ocean (1). These lesser-explored ecosystems, known as cold-water coral reefs (2, 3, 4.), have garnered increasing attention in recent years due to their fascinating biodiversity and their important role as nursery for many economically important fish. However, these ecosystems face numerous threats such as bottom trawling and ocean acidification caused by climate change.
While the depths of the ocean pose challenges for research, some regions offer glimpses into these mysterious worlds. Fjords, such as those in Chilean Patagonia, provide unique opportunities to study cold-water coral communities up close. In some fjords of Northern Patagonia, corals that were previously only known from the continental slope have been discovered thriving at diving depths, adding to our understanding of these enigmatic ecosystems (5).
While the depths of the ocean pose challenges for research, some regions offer glimpses into these mysterious worlds. Fjords, such as those in Chilean Patagonia, provide unique opportunities to study cold-water coral communities up close. In some fjords of Northern Patagonia, corals that were previously only known from the continental slope have been discovered thriving at diving depths, adding to our understanding of these enigmatic ecosystems (5).
Corals are animals. Like shallow-water corals, deep-sea corals may exist as individual coral polyps, or as colonies containing many polyps of the same species. Many individuals or colonies can make up coral banks or coral reefs. Individual polyps are much larger than those of their tropical counterpart and can grow up to more than 40 cm in length and 7 cm in diameter. They live in water as cold as -1ºC and depth down to 6000 m. Unlike their shallow-water counterparts, deep-sea corals don’t rely on symbiotic relationships with algae which need sunlight for survival. Instead, they derive their energy and nutrients from capturing tiny organisms carried by ocean currents. Over the past two decades, advancements in technology have allowed
To date, more than 3,300 species of cold-water corals are known, and new species are continuously discovered (6). They come in a great variety of colours – yellow, orange, red, purple and more. The shapes of these deep-water corals are highly variable including branched, fan-shaped, and feather-shaped. Their size equally varies from the size of a grain of rice, to tree-like colonies as tall as 10 m, and massive reefs that stretch for example from Norway to the coast of Africa.
To date, more than 3,300 species of cold-water corals are known, and new species are continuously discovered (6). They come in a great variety of colours – yellow, orange, red, purple and more. The shapes of these deep-water corals are highly variable including branched, fan-shaped, and feather-shaped. Their size equally varies from the size of a grain of rice, to tree-like colonies as tall as 10 m, and massive reefs that stretch for example from Norway to the coast of Africa.
Not only are deep-sea corals more diverse than ocean scientists ever imagined, they are also amazingly old. A gold coral (Gerardia sp.) found off the coast of Hawaii was about 2,742 years old and a black coral (Leiopathes sp.) about 4,265 years old. These coral colonies are the oldest recorded marine organisms. Due to the continuous regeneration of new polyps, some deep-sea coral reefs have been actively growing for as long as 40,000 years. And there may very well be even older deep-sea coral reefs or colonies out there..
The distribution of deep-sea corals spans the globe, from the waters of Canada, the UK (5 min. documentary narrated by Sir David Attenborough), Ecuador, and New Zealand to the icy depths of Antarctica. They live on continental shelves and slopes, in deep-sea canyons, and seamounts. In some regions, they can also be found in shallow waters, e.g. in fjords of Chile (7) and Norway. Deep-sea corals are so-called “ecosystem engineers” and play a crucial role building habitats (called marine animal forests: 8) for a myriad of marine life, including many commercially important fish, shrimps, and crabs. The corals offer food, places to hide from predators and nurseries for juveniles, and a solid surface where invertebrates can take hold. Moreover, these ecosystems hold potential for the discovery of new medicines, with some organisms found in deep-sea coral habitats showing promising bioactive properties.
The distribution of deep-sea corals spans the globe, from the waters of Canada, the UK (5 min. documentary narrated by Sir David Attenborough), Ecuador, and New Zealand to the icy depths of Antarctica. They live on continental shelves and slopes, in deep-sea canyons, and seamounts. In some regions, they can also be found in shallow waters, e.g. in fjords of Chile (7) and Norway. Deep-sea corals are so-called “ecosystem engineers” and play a crucial role building habitats (called marine animal forests: 8) for a myriad of marine life, including many commercially important fish, shrimps, and crabs. The corals offer food, places to hide from predators and nurseries for juveniles, and a solid surface where invertebrates can take hold. Moreover, these ecosystems hold potential for the discovery of new medicines, with some organisms found in deep-sea coral habitats showing promising bioactive properties.
Deep-sea corals also serve as archives of Earth’s climate history, with their skeletons providing valuable insights into past ocean conditions. By studying these ancient structures, scientists can decipher the effects of climate change and ocean acidification over time. The layers of coral growth, akin to tree rings, offer a timeline of environmental changes, enabling researchers to understand the long-term impacts of human activities on marine ecosystems.
Technological advancements, such as multibeam sonar and underwater vehicles, have revolutionized our ability to explore and study deep-sea coral habitats. These tools allow scientists to create detailed 3D maps of the ocean floor, pinpointing areas where deep-sea corals might thrive. Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) enable researchers to venture into the depths, capturing close-up images and collecting samples for further study.
Technological advancements, such as multibeam sonar and underwater vehicles, have revolutionized our ability to explore and study deep-sea coral habitats. These tools allow scientists to create detailed 3D maps of the ocean floor, pinpointing areas where deep-sea corals might thrive. Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) enable researchers to venture into the depths, capturing close-up images and collecting samples for further study.
Despite their resilience, deep-sea corals face numerous threats (9, 10), including damage from fishing gear, oil and gas exploration, and climate change-induced ocean acidification. Excess amounts of carbon dioxide from the atmosphere is absorbed by the ocean and changes its chemistry, causing slower growth and weaker skeletons in corals and other animals which rely on calcareous skeletons. Bottom trawling poses another significant risk to deep-sea corals: decades of this destructive fishing practice has resulted in habitat destruction by smoothing out the sea floor. Additionally, accidents such as oil spills can have devastating effects on deep-sea coral communities, leading to long-term damage and slow recovery.
More and more people are recognizing the critical importance of preserving deep-sea corals, also for the benefit of many fisheries since the habitats constructed by these ecosystem engineers are home to the juveniles of many economically important species. Conservation efforts are necessary to protect these fragile ecosystems, including the establishment of marine protected areas and sustainable fishing practices. However, individual actions are also crucial: by reducing carbon emissions, making informed seafood choices, and supporting organizations dedicated to coral protection, we can all contribute to preserving these invaluable treasures of the ocean.
Corals have existed for millions of years, but now their future is in jeopardy. Better protection alone is no longer enough to ensure their survival on a large scale. Combating climate change is a top priority and lies in our own interest as well. Local stress factors such as overfishing and pollution must be eliminated. At the same time, reefs must be actively supported by applying restoration
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