Water / Eau

Coraux des grands fonds du Canada Atlantique

Au cours de l’été 2002, un agrégat vivant de corail récifal fut découvert à environ 150 km à l'est de Canso, en Nouvelle-Écosse. Compte tenu des intérêts commerciaux des industries de la pêche et du pétrole, les coraux du Canada Atlantique ne sont pas à l'épreuve des impacts humains, même s'ils sont en  eau profonde et loin de la côte. En Europe, on a estimé que plus d'un tiers des coraux ont été endommagés par le chalutage. Au Canada  Atlantique, on appelle ce genre de pêche "la pêche à la drague".

En matière de gestion océanique, protéger les aires riches en coraux est une approche "écosystémique" sage, mais plusieurs des agents de protection des milieux marins croient que seule cette méthode ne garantira pas que la biodiversité marine associée aux coraux sera adéquatement protégée contre les perturbations nuisibles. Il faut mettre en oeuvre aussitôt que possible d'autres stratégies écosystémiques globales pour la protection des pêches et de notre patrimoine océanique.




























Deep Sea Corals
of Atlantic Canada

Martin Willison
N.S. Chapter of the Canadian Parks & Wilderness Society

October 2002

ost corals are colonies of small animals related to sea anenomes (coelenterates). Each individual animal is a coral polyp. It looks much like a sea anemone except that it is smaller. The polyps make a collective home for themselves by secreting a skeleton of some kind on which the colony lives. The secretions are characteristic of the species and can become very large. Some stony corals (Order: Scleractinia) form mounds called "coral reefs" that ultimately can become the size of a mountain.

(photo: John Batt, Dalhousie University, Sept. 2000)

This boulder reef was found about 3 km offshore Nova
Scotia at a depth of about 35 metres. The boulder is
covered with small soft corals called Gersemia. These
corals belong to the Order: Alcyonacea.

Many people believe that corals are found only in the waters of tropical oceans and seas. This common misapprehension is a result of the fact that near-surface coral reefs arise only in, or near, the tropics. These are easy to see, and so their absence from the shores of places like Atlantic Canada is very obvious. However, in the summer of 2002, a living aggregation of a reef-forming coral was found about 150 km east of Canso, in Nova Scotia.

The deep-water coral found near Canso is called Lophelia pertusa. It is a scleractinian, just like the reef corals of the tropics. Thousands of Lophelia reefs are known from the coastal shelves of Europe, from Portugal to northern Norway. The largest of these reefs cover several square kilometres and are 20 to 30 metres high. They are found off central Norway at depths of about 400 metres. Even though the water in which they are found is fairly cold (about six degrees), the diversity of life associated with Lophelia is similar to that found among tropical corals. Like their tropical counterparts, the deep reefs are magnets for marine life.

At of the time of writing (October 2002), three Lophelia locations have been found on the Scotian Shelf, east of Nova Scotia, but it isn't known whether all of the colonies are still alive. In Europe, several of the reefs have recently been legally protected, and a major scientific program to study them is underway. This is called the Atlantic Coral Ecosystem Study. This study has not yet been extended to the Canadian coral reefs.

Almost thirty species of corals are known from Atlantic Canada. All but one of these is not reef-forming. The other corals are either solitary (such as Flabellum), or form tree-like aggregations with a main stalk and branches (such as Paragorgia). These "tree corals" are also known as seafans. They vary in height according to species, from a few centimetres to a few metres in height. Most of them are classified as "horny corals" (Order: Gorgonacea). This name relates to the pliable skeleton that the polyps secrete. The same "magnet" principle applies to the tree-like corals. They provide habitat for many other marine animals such as fish, shrimps, and other invertebrates.

(photo: Andre Freiwald, University of Erlangen and ACES)

The reef-forming coral Lophelia pertusa is shown
here with a cusk, a
relative of cod. This photograph
was obtained in Norwegian waters, where
deep-water coral reefs are abundant

Deep-water corals feed by filtering particles from ocean currents. They eat plankton and detritus. The large ones need stable substrates to sit on, such as shell mounds, boulders and bedrock. This need for hard substrates and strong currents means that the large corals tend to be concentrated along the edge of the continental shelf. Some of the same areas are favoured by commercial fishermen and the petroleum industry.

As a result of the interests of the fishing and petroleum industries, the corals of Atlantic Canada are not immune from human impacts, even though they are in deep water, far from shore. In Europe it has been estimated that over a third of the reefs have been damaged by bottom trawling. In Atlantic Canada, this kind of fishing is called "dragging".

In Nova Scotia and Newfoundland, groundfish draggers and shrimp trawls mow down large corals, and scallopers bring up small corals. Other methods of fishing do less damage, but longlines and bottom-set gillnets also bring up corals sometimes. In addition, fishermen lose these fishing gears among corals as a result of the gear getting snagged on the corals. Lost gillnets continue to catch and kill fish after they are lost, and so the combination of the coral magnet and the fish-killing gill net is especially lethal.

With the recent collapses of many fisheries in Atlantic Canada, fishermen have moved further off shore and into deeper water in search of catches. This has brought them more into contact with previously untouched coral groves and reefs. The living Lophelia coral mound discovered on the Scotian Shelf in 2002 had, for example, been almost completely destroyed by fish draggers.

(photo: ROPOS, Sept. 2002)

These Gorgonian corals were photographed
about 100 miles south of Nova Scotia at a depth
of about 400 metres.  The Paragorgia and
Primnoa corals are around 1 metre in height.
Redfish typically aggregate around these
corals as seen here.

A large aggregation of Gorgonian corals lies in a channel between Browns Bank and Georges Bank, about 150 km south of Nova Scotia. In June 2002, the Department of Fisheries and Oceans closed part of this coral-rich area to fishing by using provisions of the Fisheries Act. This approach to protecting corals may be more widely used in future because it will benefit both life in the sea and fisheries by protecting marine habitat.

Protecting coral-rich areas is a sensible "ecosystem-based" approach to ocean management, but many marine conservationists believe that this method alone will not ensure that Canada's coral-associated marine biodiversity will be adequately protected from harm. Additional comprehensive ecosystem-based strategies for protecting both fisheries and our ocean heritage need to be implemented as soon as possible.