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Deep-sea cold-water coral acts as fish nursery

This rare in situ picture shows a redfish close to a sea pen. Fisheries and Oceans Canada photo


By Kelly Foss

A PhD student affiliated with the Departments of Biology and Ocean Sciences has discovered that deep-sea cold-water corals are being used as nurseries for certain types of fish. The discovery is making big waves in the ecology community and may lend strength to the argument that these corals should be protected.

Sandrine Baillon was using a microscope to study sea pens, soft corals that may exhibit a feather-like appearance, much like a quill pen, when she found the first larvae trapped amongst the sea pen's polyps. Upon checking other samples she found more and more larvae, sometimes as many as 200 on a small coral. The corals had been collected as bycatch during trawling excursions undertaken by the Department of Fisheries and Oceans (DFO) in the months of April and May.

"I studied several years' worth of frozen samples collected during those months and found the larvae on several sea pens and soft corals but none on samples collected in other months," said Ms. Baillon.

"Most people studying the deep sea are doing so with remotely operated vehicles (ROVs)," added Dr. Annie Mercier, Ms. Baillon's supervisor.

"Unfortunately the ROVs typically go out in summer when the weather is nice. What Sandrine found is that we'll never see larvae on corals collected at those times. We would miss them entirely."

Using the molecular signature of the larvae, the researchers were able to identify them as redfish, a species that is commercially fished worldwide. Some of the corals on which the larvae were found are also cosmopolitan species, so Dr. Mercier says the finding has significance around the world.

"Deep-sea corals are attracting attention in terms of conservation and researchers are trying to figure out what role they play, ecologically and in the fisheries," explained Dr. Mercier. "The best argument for conservation of corals is to classify them as essential fish habitat – that they are crucial for the growth, reproduction or feeding of fish."

She says there's some correlative evidence linking the presence of greater stocks of adult fish among other types of deep-sea corals, so they are being protected in certain regions. But deep-sea soft corals have not been classified this way so far.

"Just because you have adult fish in a certain area, it doesn't mean you will find the nursery area in the same place," said Ms. Baillon.

"Adults may like certain areas, but they go spawn and release larvae somewhere else," agreed Dr. Mercier. "That may be why people have never seen this before. They were chiefly looking for adult fish."

Dr. Mercier says what Ms. Baillon has discovered, with the presence of fish larvae in the sea pens, is the best argument so far to classify deep-sea cold-water corals as essential fish habitat. She also says that conservationists have been eagerly awaiting proof that would have the potential to help them argue for the establishment of protected areas.

A paper co-written by Ms. Baillon, Dr. Mercier, Jean-Francois Hamel and Vonda Wareham of DFO regarding these findings has been featured in the journal, Frontiers in Ecology and the Environment, a publication of the Ecological Society of America. It was also featured as editors' choice in a recent issue of Science magazine.