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Oasis of the Deep: Cold water corals of Atlantic Canada
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 and produce much needed food
from the sun’s energy to share with their animal hosts. Cold-water corals do not contain
microscopic plants 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. There are many varieties of cold-water corals which exhibit a wonderful
diversity of shapes, colours and sizes.
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.
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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 group 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, this skeleton lies within the body wall of the
polyps. This 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
thousands of years old. In some species, each year of growth manifests itself in the form of
distinct growth rings, similar to a tree. These rings are providing scientists a valuable window
into the ocean climate of the past.
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 significant populations of
corals in the deep waters off Newfoundland and Labrador.
In the deepest waters yet explored in Atlantic Canada -- some 2.5 kilometers --, 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
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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! Usually sea pens stay in one spot but they are able to uproot themselves and
gradually relocate to take advantage of favourable currents. Some can also forcibly expel water
out of themselves propelling them deep into the sediments in the blink of an eye!
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. Polyps of the
bamboo corals are unable to retract. 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
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abundantly where fishing takes place and are probably the best known of the cold-water coral
species.
Scientists have been researching and collecting information on cold-water corals in Atlantic
Canada.
Research has focussed on collecting more detailed information on their distribution, abundance
and physiology.This knowledge is being used to make informed management decisions regarding
their protection from human activities.
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 also provides 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 make 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 public and government agencies.
As part of an integrated approach to oceans management, the conservation and protection of
corals is a key objective for monitoring and maintaining the variation of life forms – or,
biodiversity – within these unique areas. This includes, working with the fishing industry,
regulators, scientists and the public to identify areas of research and management concern. For
example, scientists have been working with fish harvesters and independent at-sea observers to
identify and collect corals caught as by-catch.
Scientists are working to understand and assess the impacts of human activities on deep-water
corals. Based on the available information, measures have to be taken to conserve the health of
vulnerable coral communities and minimize the impacts from human activities on coral habitats.
Where necessary, there is also the need to restrict human activities to protect and restore the
more important coral habitats.
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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 is a large submarine canyon on the eastern seaboard of North America and is located
on the Scotian Shelf, South of Halifax near Sable Island.
The Gully MPA 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 there, including many species of cold-water corals. These corals are present in
many parts of the underwater canyon and many types of activities are restricted or limited.
The world of the cold-water corals remains a mystery. Continued exploration off the deeper
waters of Canada’s coasts is needed to document their life history, distribution and habitats. So
little is known about cold water corals that 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 made.
While great progress has been made, if this 1 week excursion is any indication, then much more
research and exploration needs to be done to gain a more thorough understanding of deep-water
corals. This 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, and continue to contribute to the amazing diversity of
Canada’s marine ecosystems for generations to come.
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