Studying the Enriching Effect of Submarine Canyons

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.

An image showing the canyon in relief.

The du Couedic submarine canyon, south of Australia. The colour scale indicates depth, with red corresponding to the shallow area and purple to the deepest area. The canyon course (blue) allows deep ocean currents to reach the continental shelf. Image: © 2015 Conlan et al.

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.

A map.

Underwater depths off the southern coast of Australia. The two rectangles correspond to the underwater canyons where the research took place. Image: © 2015 Conlan et al. (licence: CC BY 2.0). From “Macrofaunal Patterns in and around du Couedic and Bonney Submarine Canyons, South Australia”, by K.E. Conlan, D.R. Currie, S. Dittmann, S.J. Sorokin, E. Hendrycks (PLoS ONE 10(11): e0143921; doi:10.1371/journal.pone.0143921).

David had already studied the fish and large invertebrates in these canyons. Because I specialize in small invertebrates, he generously invited me to see if they were responding in the same way.

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.

Three photos: A man grasps a sampler that hangs overhead, a sampler hangs over the surface, the ship at port.

In these images from the Southern Surveyor in February 2008, researcher David Currie operates the sampler on the ship’s deck. Images: Graham Hooper © David Currie

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.

Photo of a worm specimen with a 0.5 mm reference scale and the scientific name "Prionospio steenstrupi".

Canyon heads support numerous species, like this little polychaete Prionospio, which lives in a self-made tube and captures passing particles with its elaborate appendages. Image: © Washington State Department of Ecology’s Marine Sediment Monitoring Team (license: CC BY 2.0).

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.

This entry was posted in Animals, Fieldwork, Research, Species Discovery and Change, Water and tagged , , . Bookmark the permalink.

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