Sponge Blob Rare Plants

March 4, 2015

At 160 metres beneath the ocean waves, it's snowing hard. Streams of sediment, particulates, and bacteria drift past the wide-angle lenses of the robotic submersible as it descends. "We're getting close, guys," University of Alberta biologist Sally Leys tells its pilots. "I see the bottom. Slow…" From the grey/brown sea floor loom shrubs of sea sponges in pale yellow and dish-glove orange. "Aren't they pretty?" Leys asks. Images of tubular sponges — like a cross between a brass instrument and giant cannelloni — fill the video feeds.

This is the first day of Leys's annual research cruise off the Vancouver coast studying the glass-sponge reefs and how they make their living in the deep. Already she and doctoral student Amanda Kahn have discovered that sponge reefs filter massive quantities of water (9,000 times their body mass in a day), fertilize the oceans with nitrogen, and sequester huge amounts of carbon. It turns out these sponge reefs, an ecosystem no one even knew existed in the Georgia Strait until 2001, are a hidden but invaluable part of the marine ecosystem.

The next question is just how much oxygen these sponges need to make a decent living.

Deep-sea glass sponges span the Pacific coast from Washington up to Alaska, but only in B.C. do they form such massive reefs, growing over their dead ancestors like coral. The reef shown on the camera feeds aboard the Canadian Coast Guard research ship Vector rises off the benthic floor as high as 20 metres and is estimated to be between 6,000 and 9,000 years old.

 

There are a dozen such reefs between Vancouver and Vancouver Island. This one, the Fraser Ridge Reef, curves like a banana for almost a kilometre. Such sponge reefs, fossil walls of which can still be seen all over Europe, used to limn the ancient Earth's shores. When sponge reefs were found extant in Hecate Strait in the late '80s, it was akin to finding a living fossil: people had believed they were long extinct.

On this research cruise, the robotic submersible will be manipulated from Vector to insert oxygen and flow sensors into the sponges' inch-wide chimneys. It's delicate work. The sponges have the consistency of meringue, while the submersible — ROPOS, or Remotely Operated Platform for Ocean Science — is the size of a small walk-in cooler and weighs over three tonnes. "I'm thinking about that one there," says ROPOS supervisor and pilot Keith Tamburri as he steers it over to an outcrop. "I bet we could thread the needle on that one." He gestures to the camera feed, pointing out a particularly fetching chimney. Once deployed, the sensors will record water flow and oxygen draw, helping to paint a picture of the sponge's metabolism and energetics.

"Studying sponges' ability to exist with low oxygen and how much food they take up is sort of like a window into a very long past," says Leys. To look at a sponge reef is like going back to a time before the seas were even that salty and long before they became the domicile of fish. "This is what the early ocean looked like," Leys says, pointing to the murky greenish-blue sea floor, dotted with shrublike sponge growths, on the screen. "Only there was no organic snow, because plants hadn't colonized land yet."

There is something both profound and comforting about beholding one of Earth's earliest animal life forms. To see such an ancient relative thriving a stone's throw from Canada's busiest port is remarkable, and to know that this life form was already on the planet some 545 million years ago is one of the most comforting thoughts I've had regarding the natural world. It humbles our existence to the point that all the worries of today drift away. On the ocean floor, life is dark, it is peaceful, and it just is.

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