When Canadian scientists discovered ancient glass sponge reefs off B.C.’s coast 40 years ago, they were both elated and concerned.
Elated because the reefs — which look like futuristic condos and grow as tall as eight-storey buildings — were thought to have gone extinct 40 million years ago. One excited researcher said it was like “discovering a herd of dinosaurs on land.”
And concerned because large chunks of the reefs, which are deep-sea biodiversity hot spots, were dead.
Did the reef die-offs occur hundreds or thousands of years ago — or did they occur more recently, due to changing ocean conditions? Did human activity cause their demise? And is there any hope the dead areas can grow back?
Federal research scientist Anya Dunham and five of her colleagues set out to answer those questions by studying glass sponge reefs in Howe Sound near Vancouver, Chatham Sound near Prince Rupert, and Hecate Strait near Haida Gwaii.
Their research, which will be published in August in the journal Estuarine, Coastal and Shelf Science , shows that damage caused by bottom-contact fishing likely killed the reefs, some of which are more than 9,000 years old.
“It points the finger to humans as the culprit of reef demise,” Dunham, who works for Fisheries and Oceans Canada, told The Tyee.
But there’s good news as well.
In both living and dead reef areas, researchers found baby glass sponges — teeny creatures the shape of a vase — searching for a place to anchor.
If what’s left of the reefs remains healthy, the living sponges “could send their larvae, the baby sponges, into those damaged areas,” Dunham said.
“If the dead skeletons of the previous generations are solid enough, those baby sponges might be able to anchor and continue growing. And if that happens, then those areas would become functional again.”
‘Cities of glass’
Glass sponges are found in oceans all over the world. But living glass sponge reefs exist only along the Pacific Northwest coast, where the water is cold and contains high concentrations of silica.
The sponges filter silica out of the water and make spicules, which form the skeleton of the sponge. New sponges settle on top of skeletons from previous generations to build what Dunham calls “cities of glass.”
The living reefs filter water and provide homes for more than 100 species, including rockfish, spot prawns, sea stars and squat lobsters. The reefs also sequester about the same amount of carbon per square metre daily as kelp forests and old-growth forests, according to Dunham.
Glass sponges filter water and provide homes for more than 100 species, including rockfish, spot prawns, sea stars and squat lobsters.
Photo via BC government .
Scientists already had evidence that bottom-contact fishing, such as trawling and dredging, destroys and damages glass sponge reefs.
But Dunham said this is the first time that researchers have matched historic fishing records to the dates that large sections of the reefs perished, ruling out death from natural causes.
The study’s findings counter the argument that glass sponge reef protections aren’t needed because the reefs died a long time ago, so “maybe it’s not humans that are causing the damage,” she said.
To date the reefs, Dunham and her colleagues used remotely operated vehicles and ship-based sampling to drive tubes into the sea floor and extract sediment samples. They couldn’t use radiocarbon for dating because glass sponges, unlike corals and bivalves such as clams, don’t contain carbonates.
Dunham said the age of the sediment around a reef reveals when death occurred.
All the areas the scientists sampled had died over the past 70 years. Parts of the Carmelo Point glass sponge reef in Howe Sound, near Bowen Island, died over the past 20 years.
“Many of those areas had been quite heavily fished in the past, and some of that happened even before the reefs were known to science,” Dunham said.
Fishing can damage reefs by crushing them, either through trawling, trolling or placing traps on the delicate reefs. “But there’s also damage through sediment disturbance, [from] dragging gear across the sea floor,” she said.
Four glass sponge reefs in Hecate Strait and Queen Charlotte Sound are safeguarded in a marine protected area.
But the 12-kilometre-long Chatham Sound reef — one of the largest living reefs ever discovered — is not protected, though the sound has been closed to the groundfish trawl fishery since 2012 as part of a coast-wide habitat protection initiative.
The Chatham Sound reef was discovered in 2013 by crews surveying for a proposed underwater liquefied natural gas pipeline route.
When Dunham and her colleagues surveyed the reef, they found about 90 per cent of it was dead, with some areas looking like “glass sponge rubble.” But they also saw baby sponges everywhere.
“So there is some hope that that area can come back to life, and perhaps especially so if protection is extended to that area,” Dunham said.
Glass sponge reefs nee…
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