Over the last seven years, Canadian Museum of Nature marine biologist Kathy Conlan and her colleagues identified more than 500 species collected in two submarine canyons on the South Australian coast, comparing the marine life inside and outside of the canyons. This and other studies are demonstrating the importance of submarine canyons to coastal marine life worldwide.
Submarine canyons incise the shelf and slope of all the continents in the world and nearly 6000 are known so far. They are created by river flows from the continents and by sediment failures along the shelves.
Submarine canyons focus deep-ocean currents onto the continental shelves, where the currents inject nutrient-rich water at shallow-enough depths for phytoplankton to take advantage of them. They also funnel land waste downwards so that they have become a convenient underwater garbage pit. Fish tend to congregate in canyons to feed on zooplankton concentrations there, so these canyons are also a favourite target for fishing.
In 2009–2010, I took a year’s sabbatical in Australia at the South Australian Research and Development Institute with David Currie, Ph.D., and at Flinders University with Sabine Dittmann, Ph.D.
David had recently collected samples from two submarine canyons on the South Australian coast. These canyons were thought to be important to the survival of a nearby sea-lion colony and to support the lucrative tuna, sardine and anchovy fishery there.
These critters, which live on the sea floor or burrow underneath, are good indicators of environmental effects because they aren’t very mobile, so they can’t get out of the way of pollution or natural changes. So their distribution patterns would likely reflect the effects of the canyons.
David methodically sampled inside and outside the canyons at 100, 200, 500, 1000 and 1500 m depths. He used a grab that sampled a known area of sea floor so that we would be able to compare abundance and biomass at each of the 27 sites.
That was a feat in itself: targeting precise locations from a rolling ship with a sampler hanging from a 1000 m of cable or more that frequently failed at such great depths.
My job seemed much easier: pick out of the mud the roughly 3000 animals that he had captured, then identify, count and weigh them, and finally, analyse their distribution patterns to see if we could see a canyon effect.
This looked like a simple job until I realized that Australia has a way more diverse marine fauna than Canada. Fortunately, Shirley Sorokin, Ed Hendrycks, Val Tait and Shea Cameron joined the project.
The result was the discovery of 531 species of worms, clams, snails, starfishes, sponges, shrimps and many, many more. Their abundance, biomass and diversity were highest on the continental shelf, and species composition shifted at the canyon heads.
This shift indicated that the canyon heads had strong currents that were enriching the coast. Our results were published last autumn by the open-access journal PLoS ONE, thanks to support from the Canadian Museum of Nature and a Visiting Scholar grant from Flinders University.
This collection is now housed at the South Australian Museum, where we hope it will be useful for other researchers. Our identification of such a rich area is being used as ammunition to convince policy makers to protect this coast better.
Canada has many submarine canyons of its own. Perhaps the most famous is the Gully, a designated marine protected area near Sable Island off the coast of Nova Scotia.
Canyons may be sanctuary for many undescribed species—just ask Jean-Marc Gagnon, Ph.D., a marine biologist here at the Canadian Museum of Nature who recently identified a new species of file clam from the Gully.