Oasis of the Deep: Cold Water Corals of Canada


Narrator: Two-thirds of the surface of the earth is covered by the ocean and ninety per cent of that lies beyond the continental margins in depths greater than 2 kilometres.  These areas remain largely unexplored, making the deep ocean truly the last frontier on earth. 

Living in these deep waters are animals that have adapted not only to the lack of sunlight and the cold temperatures which rarely go above 2 degrees Celsius but also to the pressure of the water which can reach 1000 kilograms per square centimetre!

Yet in this seemingly inhospitable environment there is a wealth of life, including a group of animals known as cold- or deep-water corals.

When we think of corals we usually think of coral reefs which are found in shallow, tropical waters.  These more familiar relatives of the cold-water corals are restricted to the sun-lit waters because they rely on microscopic plants which live in their cells, producing and produce much needed food from the sun’s energy to share with their animal hosts.  Cold-water corals do not contain these algal symbionts and so are free from the shackles of the sun and are able to live at depths in excess of 4 kilometres.

Even though the existence of cold-water corals has been known since the 18th century, it is only recently, in the last decade or so that scientists have been able to observe them in their natural habitats.  This has been made possible by the use of deep-water cameras and submersibles, such as the Canadian-made Remotely Operated Platform for Ocean Science (ROPOS). ROPOS and other deep-sea submersibles have given researchers the ability to collect videos and still images, to measure organisms with calibrated lasers, and to retrieve samples during deep-sea surveys. 

Corals share many characteristics with the anemones and jellyfish and are grouped together with them and others in the Phylum Cnidaria.  Of these, the corals and anemones are the most closely related.  They both belong to the Class Anthozoa which itself is divided into three major groups.  One group, the Subclass Octocorallia, includes the soft corals, sea fans, bamboo corals and sea pens.  The Subclass Hexacorallia includes stony corals, and black corals belong to the Subclass Ceriantipatharia.

Coral colonies are composed of anemone-like animals called polyps. A single coral polyp may be as large as a dinner plate or smaller than the head of a pin.  Polyps may be solitary but more commonly, many work together to form a co-operative colony. These colonies capture passing food particles from the water which includes both dead material and live animals. For one group called the octocorals, the polyps all have 8 finger-like tentacles which capture food particles from the surrounding water. Virtually all octocoral species form colonies. 

In contrast, stony or hexacoral polyps have multiples of 6 tentacles and are different from octocorals in that most of the species within this group are single polyps, with only about a quarter of them forming colonies. Stony corals are also the only groups which are able to form extensive deep-sea coral reefs. 

Corals are able to extract calcium carbonate from the seawater to produce a skeleton to support the polyps.  In soft corals, sea fans and sea pens, the skeleton lies within the body wall of the polyps. This inner skeleton helps strengthen the coral while maintaining flexibility. The stony corals have employed a different tactic: each polyp secretes a cup-shaped skeleton around itself forming a hard outer covering. 

Both soft and stony corals can support massive colonies, and the bubblegum coral Paragorgia arborea has been recognized as the world’s largest marine invertebrate species, with confirmed reports of colonies reaching 6 metres in height and unconfirmed reports of 10 metres! Coral colonies also provide habitat for many fish and bottom-dwelling creatures, like sea stars, shrimp, and anemones. 

Many cold-water coral species are slow growing and tremendously long lived.  In fact, there are records of individual corals of some species reaching nearly 1,000 years, while coral reefs can be many thousands of years old.  In some species, each year of growth manifests itself in the form of a distinct growth rings, similar to a tree.  These rings are providing scientists a valuable window into the ocean climate of the past.

Dr. Evan Edinger: “This is a skeleton of Primnoa resedaeformis. There is a great deal of interest in the skeletons of deep-sea corals because they are very good oceanographic recorders and they record water temperature or particular variations in water masses that affected the coral while it was growing.  This species Primnoa resedaeformis is particularly good for that because the nature of its skeleton is that it has these very fine growth bands recorded in it.  It’s in alternating layers of calcite and a protein called gorgonin.  So from the calcite we can extract information about the temperature of the water in which the coral grew and from the gorgonin we can extract information about what the coral was eating or information about different water masses that affected it while it was growing.”

Narrator: More than 700 species of cold-water coral occur world-wide.  Off Nova Scotia and New Brunswick at least 45 species have been documented and it is likely that more remain to be discovered. Many species of cold-water corals are common throughout Atlantic Canada, in both shallow and deep waters. Knowledge of the corals' distribution has been gained from both fish harvesters and the scientific community. Atlantic Canadian fishing communities are aware of many types of cold-water corals as samples have been retrieved by their fishing gear. Some species have developed very specialized habitat requirements.  Most corals grow on stable bottoms such as boulders and bedrock, but some are anchored in soft sediments. 

The large deep channels of the continental slope off both Nova Scotia and Newfoundland are home to the greatest abundance and diversity of deep-water corals in Atlantic Canada.  Some of the most studied areas to date include the Northeast Channel, the Gully, and the Stone Fence, an area along the steep continental slope.  As well, there is evidence of a significant population of corals in the deep waters off Newfoundland and Labrador.

In the deepest waters yet explored in Atlantic Canada -- some 2.5 kilometres  --  sea pen fields project above the featureless ocean bottom.  About a dozen species have been identified and not all look like the old-fashioned quill pens from which they take their name.  Unlike other octocorals, a sea pen's polyps are specialized to specific functions: a single polyp develops into a rigid, erect stalk called the rachis, and loses its tentacles, forming a bulbous "root" called the peduncle, which anchors the sea pen in the soft sediments of the sea floor.  Sea pen stalks can be over a metre long! Some can also forcibly expel water out of themselves propelling them deep into the sediments.

Also found on these soft sediments are at least three species of solitary cup coral.  This is a stony coral which is widespread along the continental margin of North America.  One of these, Flabellum alabastrum, is being used by scientists as a climate change indicator, providing a record of changing sea temperatures within its hard skeleton.

The rocky ledges and walls along the continental margin and other hard bottom areas support the sea fans or gorgonian corals. These are amongst the largest of the coral species and are attached to the bottom by a holdfast – similar to the root of a plant.  From this comes a large, flexible, branching tree-like structure that supports the polyps and then orients these towards the prevailing currents.  These colonies can be over a century old.  Fishers refer to these as “trees” which has led to the term “forest” being used to describe the extensive concentrations of these species which can occasionally occur.  Their bright colours and large size make them an unforgettable feature of the deep-water ecosystems.  The Northeast Channel is an area with a high abundance of these colonies, including both Primnoa resedaeformis, also known as sea corn, and the previously mentioned Paragoria arborea, or bubblegum coral.

Also growing on hard ocean bottoms are the Bamboo corals, which although they are octocorals, develop a bony internal skeleton.  Their skeleton is formed by hard calcareous segments intersected with small bands of protein. When dead, the coral skeleton is exposed and resembles bamboo.  When alive the long lightly-branched fronds sway in the currents.  One of the deepest recorded occurrences of all deep-water corals is a bamboo coral which was discovered at almost 5 kilometres below the surface of the ocean.

The black corals are named for the black or brown colour of their skeleton -- not their outer appearance.  They are rarely encountered in Canadian waters but can be recognized by the tiny protective spines along their branches.  These spines give them their other name of thorny coral.

Of these many species only one is capable of forming underwater reefs.  That is the coral, Lophelia pertusa, also known as spider hazards.  Lophelia is a stony coral and is easily recognizable by its’ brilliant white colour, although it can also be shades of pink or yellow.  Lophelia reefs can form mounds to 35 metres high, as the small layer of living colonies grows on top of the old skeletons.  Their reach can be hundreds of metres wide, and the largest recorded reef can be found off Norway and measures 13 kilometres long.  The only known lophelia reef in Canada is found at the Stone Fence, although small colonies have been discovered in the Gully Marine Protected Area (MPA).

The top of the banks in some coastal waters, and the crests of the continental margin are dominated by the soft corals.  These smaller corals are soft and fleshy as their name suggests and when disturbed some are able to retract into what looks like pincushions.  Soft corals are found abundantly where fishing takes place and are probably the best known of the cold-water coral species.

Recent advances in non-destructive sampling technology by submersibles, has allowed Atlantic Canadian researchers to collect genetic samples used to assist in the identification of corals. Analysis of coral genetics can also provide insights into how they reproduce and how different populations of coral are related to one another.

So far genetics have been used to prove that photos of what were thought to be a coiled wire coral were misidentified.  The genetic fingerprinting revealed it actually to be an egg-case of a flatworm!

Scientists have also learned that the bubblegum corals in the Northeast Channel Coral Conservation Area are highly inbred, resulting in reduced genetic diversity, and do not reproduce by forming an exact replica of the parent through budding or fragmentation, but rather by some form of sexual reproduction.

Many corals contain potent chemicals of interest to biology, medicine and industry. For example some species of gorgonian sea fans are considered a medical resource for their high level of hormone-like compounds. Other corals have been found to possess anti-tumour promoting characteristics which are being used in cancer treatment trials.

Their upright and fragile nature makes many species of coral vulnerable to physical contact.  Human activities such as fishing and hydrocarbon extraction have the potential to seriously damage cold-water corals.  As many corals are also slow growing, recovery from disturbances may take many years.  As well, corals may be very vulnerable to the effects of climate change as some species rely upon specific temperatures for survival.  As a result, the conservation concerns for cold-water corals have come to the attention of the public and government agencies.

Since 2002, Fisheries and Oceans Canada (DFO) has implemented specific conservation measures under both the Fisheries Act and the Oceans Act to protect key coral habitats.

In June 2002, DFO established a 424-square kilometre Coral Conservation Area in a portion of the Northeast Channel with the objective of protecting high densities of intact octocorals -- mainly bubblegum and seacorn coral.

In September 2003, DFO scientists observed mounds of the reef-building coral spider hazards -- or lophelia pertusa -- at the Stone Fence, southeast of Cape Breton, Nova Scotia. The reef is made up of both living and dead coral, and has been damaged by fishing activity over the past few decades. The 15-square kilometre Lophelia Coral Conservation Area was put in place in June 2004 and a small area surrounding the entire reef was closed to all bottom fishing.

The Gully MPA (Marine Protected Area) was designated by regulation in May 2004 under Canada’s Oceans Act.  One of the objectives for the creation of this MPA is to protect the rich diversity of marine habitats and species found in the Gully, including many species of cold-water corals. These corals are present in many parts of the underwater canyon and numerous activities are restricted or limited.

With so little known about cold-water corals, each scientific mission brings new and exciting discoveries.  In just 1 week of working in both the Gully MPA and Stone Fence Coral Conservation Area in 2007 eight new records of coral species in Canadian waters were observed.  While great progress has been made, much more research and exploration needs to be done to gain a more thorough understanding of deep-water corals, their life history, distribution and habitats This new information will give DFO the tools needed to effectively and efficiently protect these long-lived, vulnerable species.  In return, deep-water corals will help scientists understand the changes in the ocean’s temperatures, provide habitat, and continue to contribute to the amazing diversity of Canada’s marine ecosystems for generations to come.