When hearing the term ‘corals’, it is easy to slip into vacation daydream-mode, picturing warm waters, vibrant colors and an occasional turtle spotting. But what if we told you that more than half of all coral species alive today take residence in icy, and much deeper waters? That holiday dreamscape is drastically altered.

Arctic Corals: A Fascinating Life

As much as conventional wisdom and island getaway advertisements would have us believe, corals are not limited to the crystal clear, warm archipelagos and lagoons of the tropics. In fact, corals thrive in the icy waters and unforgiving environments of the Arctic. These deep water corals are also found in almost all of the world’s oceans, particularly occupying continental shelves, fjords and even submerged volcanoes known as seamounts, from the harsh Canadian Arctic across the Northwest Atlantic to the more sheltered Norwegian shores. They were first discovered centuries ago when fishermen found coral fragments entangled in their deep-sea nets. It has only been in recent years with the development of sophisticated underwater technology that scientists have been able to investigate these extremely cold and deep‑water environments. Such expeditions have since revealed that not only do corals exist in these harsh waters, but that they are able to form dense and giant reefs.

Deep- And Cold-Water Coral

Cold and deep-water corals are made up of three primary groupings: stony corals, those that form the reef itself; true soft corals that float in a dandelion-esque fashion; and black corals, distinguishable by their dark chitin skeletons and surrounded by polyp webs. Together, the species in these groups create three-dimensional, coral forests spanning the sea floor; much like their warm-water cousins when examined for size and complexity. Although cold-water corals are technically restricted by their affinity for cold temperatures between 4–12˚C, this does not in fact limit their habitat all too much; they are found in both cool shallow waters towards the polar latitudes, as well as at depths of 4 km in deeper waters closer to the tropics.

Importance of Coral Reef Ecosystems

Although studies on the significance of deep-coral reefs are new and ongoing, existing research has demonstrated that these coral systems are immensely rich in diversity and species abundance, suggesting that they are hot spots for biodiversity in the deep Arctic waters. Because of their nutrient-rich existence, cold-water coral reefs provide ideal habitats for many marine species. In essence, they serve as ecosystem islands, providing nursery grounds for a wide variety of species, including many commercial fish species.

 “Coral reefs are the only living organism visible from space”

Their unique ability to build hard interconnected skeletons earned corals the nickname ‘oceans architects’, and are considered the only living organism to be visible from space. Particularly, the dense, banded skeletal structure of cold-water corals provides scientists (and anyone interested in natural life cycles) with great environmental archive indicators, serving a similar purpose to that of tree rings. Within these ancient reefs, details of past weather conditions are forever tattooed in their growth bands, exciting scientists with reef development cues dating back to the last glacial period (meaning, 8000 BC!). Even with the limited research conducted on these cold-water systems to date, it is easily recognized how important these ecosystems are for extreme underwater environments.

Adapting to The Arctic

In such extreme environments, growth and development is a slow process. For coral reefs to form their characteristically complex and dynamic structures that we know and love of them, it can take thousands of years. This complexity contributes to their niche function in the otherwise flat, featureless and seemingly endless surroundings of the arctic seafloor. Although cold-water corals are long-living, their slow growth and fragile nature leaves them particularly vulnerable to damage, of which the biggest culprit is, of course, us. 

Unlike their warm-water counterparts, cold-water corals live in the dark and so do not have the luxury of depending on light-symbiotic algae for ecosystem functioning. Without a mutualistic relationship to rely on for food, these azooxanthellate corals are entirely dependent on particulate organic matter and zooplankton for all of their nutritional needs. Cold-water corals have adapted to stretching out tentacle-like structures to act as filters that trap dead algae and decomposing animal matter caught in passing currents. (If these terms are already making your eyes cross, head over to this post that sums up coral basics really well.) 

Despite obviously being able to withstand cold Arctic temperatures, these corals are even better adapted to changes in water temperature. The Gulf Stream that encroaches on Arctic waters, as well as the regular down-welling of warmer surface waters, means that coral ecosystems need to be able to handle large temperature fluctuations anywhere from 5–15˚C. Studies have shown that they do this without showing any significant stress levels or mortality responses. This adaptability may provide a basis for further studies on how cold‑water coral ecosystems serve as keystone organisms in their response to global climate change.

Threats to Arctic Coral Reefs

Regardless of the depth at which these corals and their dense reefs occur, human activity has an immense negative impact on them, being evident in almost every cold-water coral study and/or survey undertaken to date. Both filmed and photographic evidence shows the clear destructive impact of towed fishing trawlers on the seabed, with corals lying in disconnected ruin from their once-dense reef. Their slow-growing and fragile nature means that damaged reefs have a long recovery road ahead of them, with some potentially never reforming.

Another unfriendly human population vice threatening cold-water coral reefs is in response to rising atmospheric CO2 levels as a direct consequence of fossil fuel burning. Increased CO2 levels in seawater forces alkalinity and calcium carbonate saturation ability to drop, resulting in increased acidity levels. As seawater becomes more acidic, cold- and deep‑water corals struggle to build the calcium carbonate skeletons necessary to form reefs.

Many governments have woken to the importance of the mysterious environments of the deep seas, with Norway leading the globe in their cold-water coral conservation work, while some are putting protection plans in place and others outlining future policies aimed at conserving deep-water coral reefs from excessive fishing activities. With these positive steps taken based on a relatively small amount of available data and research, we can be hopeful that with further efforts from the public and curious minds, these ecosystems will have considerable forces standing behind them.

What Can You Do for These Hidden Beauties?

1.   Educate yourself and others

If this article tugged at your exploratory heartstrings, be sure to look up organizations doing ocean research. And almost every single coastal university has one lecturer or research fellow with an oceanic passion project, just begging for interested minds. Some examples of organizations: Deep Sea Conservation Coalition; The Marine Diaries; Oceans North and World Wide Fund For Nature Canada.

2.   Joining the new generation of scientists

One rung up in the ‘educate yourself’ ladder! In order to continue this valuable research, and in some cases, pioneer efforts in new waters, a new generation of scientists is needed that are willing to explore what lives down in the dark and extremely chilly deep seas of the Arctic, as well as many unexplored regions of the ocean. In this way, these ‘new gen’ scientists will inform the public, and in turn politicians and law-makers, about what treasures are hidden down there and why it is important to protect them.

3.   Donate

As mentioned above, there are wonderful organizations out there doing their utmost to make deep-sea exploration both more accessible and available. All of these organizations and many smaller, local-to-your-area non-profits will most definitely welcome donors in the form of volunteering or monetary donations.