- A new study has found that warming ocean waters and increased acidification could weaken the skeletal structure of Canada’s iconic glass sponge reefs.
- The potential loss of glass sponge reefs, which were thought to have gone extinct 40 million years ago, would imperil the regionwide and distinct ecosystem, including potentially hundreds of fish species.
- Researchers say the Canadian government must take climate change more seriously or risk losing an ecosystem found nowhere else.
When scientists first discovered glass sponge reefs in British Columbia’s waters in the late 1980s, they couldn’t have been more surprised. Prior to this, they believed that glass sponge reefs went extinct 40 million years ago.
“If you think of it, it’s like stumbling upon a whole herd of dinosaurs in our backyards,” says Angela Stevenson, a researcher based in British Columbia who studies glass sponges intensively.
Glass sponge reefs may have outlived the dinosaurs, but they may not survive much longer. In May, Stevenson and her colleagues published a study in Scientific Reports that warns that the impacts of climate change will likely weaken glass sponges’ skeletal strength and filter-feeding ability.
The team from the University of British Columbia (UBC) explored the dual impacts of ocean warming and acidification on one of the only three reef-building glass sponge species in the world, the cloud sponge (Aphrocallistes vastus). Working in a lab, the scientists placed the sponges in conditions mimicking future projected warming and acidification, based on scenarios from the Intergovernmental Panel on Climate Change (IPCC).
While individual glass sponges are found worldwide, glass sponge reefs are unique to the Northeast Pacific Ocean. These deep-sea reefs can grow to 19 meters (62 feet) in height, and rise to 22 meters (72 feet) below sea level, allowing for scientists in British Columbia to dive to the ancient reefs and study them closely.
Warming temperatures and acidification weaken reefs
Global warming, driven by the burning of fossil fuels, affects the ocean in two key ways. The first is ocean warming, when rising global temperatures heat the surface water. More frequent storms and currents mix the warm surface water with the deeper waters of the oceans, increasing overall ocean temperature.
The second is the increased levels of carbon dioxide absorbed by the oceans. This causes a series of chemical reactions that lower the pH level of the water, leading to ocean acidification.
The process of acidification is more common than one may realize.
“When you add carbon dioxide to water, the water becomes more acidic,” says Chris Harley, a professor at UBC and co-author of Stevenson’s study. “This happens in fizzy sodas, and also happens in the ocean.”
Stevenson wanted to study how both ocean warming and acidification impact the reefs separately and also in combination with each other, which more closely represents real-life circumstances. To do this, she separated the sponges into three groups, each experiencing a different condition: warming, acidification, and a combination of both.
Stevenson observed that all three conditions decreased the cloud sponges’ filtering capacity and skeletal stiffness. The sponges’ cage-like skeletal structure, made up of tiny particles known as spicules, became more brittle under all three scenarios. (Spicules are made from silica, the same compound that forms glass, hence the name “glass sponge.”)
Stevenson found that when the conditions reduced the sponges’ skeletal stiffness, their filtering capacities also declined. This could affect the whole regional ecosystem as glass sponge reefs are vital filter feeders, combing through approximately 100 billion liters (26 billion gallons) of water daily and removing 75 to 90% of microbes that pass through them. The benefits go both ways: the reefs maintain water quality by filtering bacteria, and at the same time, the bacteria serve as a source of nutrition for the sponges.
“Alterations to the skeleton, especially in terms of reduced stiffness, could reduce feeding efficiency and lower the sponges’ critical water flow threshold,” Stevenson says.
After four months, Stevenson found that the sponges were more sensitive to ocean warming than acidification. The warming conditions reduced the cloud sponges’ filtering capacity by 5.5 times, the acidified conditions by two times, and the combined conditions by levels in between.
“In nature, acidification and warming are intertwined, and their fluctuations are not linear,” Stevenson says. Yet, when comparing the two, she finds that “warming is the biggest problem for these sponges.”
All three scenarios reduced the sponges’ skeleton stiffness by half. Stevenson also warns that rising temperatures may not only weaken existing cloud sponges, but also curtail future reef formation as a whole.
Deep-sea cities of silica
The decline of cloud sponge ecosystems will also harm its inhabitants.
“[Glass sponge reefs] provide a home to a rich community of fish and invertebrate species, who depend on them for protection, nursery grounds, and food,” Stevenson says.
In all, scientists have documented 106 species of fish and invertebrates living among glass sponge reefs, including rockfish, prawns and crabs. Stevenson says these reefs will experience biodiversity loss due to warming and acidification.
“Imagine what would happen if a big city like Vancouver or New York City were destroyed,” she says. “As these cities collapse, so does everything depending on it for food and shelter.”
Like cities, the reefs serve as a haven of resources for local inhabitants. Whether it’s protecting small invertebrates from larger predators or acting as breeding grounds for rockfish, they are vital infrastructure for the survival of marine creatures. That makes the potential impacts of warming and acidification on these reefs and their inhabitants disastrous.
More conservation needed
Local marine conservation groups are working with the Canadian government to advocate for greater protection of glass sponge reefs. One of the most prominent groups is the Marine Life Sanctuaries Society (MLSS), based in British Columbia.
Over the past few years, MLSS has brought up the importance of glass sponge reefs to the Canadian government, urging it to protect the reefs from human activity. In 2019, Canadian department of fisheries and oceans enacted the Strait of Georgia and Howe Sound Conservation Initiative, which bans bottom trawling and other bottom-contact fishing in areas with glass sponge reefs.
As the current president of MLSS and the first person to discover glass sponge reefs in Howe Sound, Glen Dennison is actively pushing for governmental protection of the reefs. He says he’s grateful that the government has banned bottom-contact fishing in the Strait of Georgia and Howe Sound’s marine refuges, but adds the current enforcement efforts are not strong enough.
“We have seen a noticeable decrease in trapping and damage from prawn traps to glass sponges, but we still need to put more resources on it,” Dennison says. “We need more boots on the ground out there.”
He recalls in particular seeing a prawn trap go down in a reef area, making a 0.4-square-meter (4-square–foot) cookie-cutter hole in a pristine reef. When he checked the area a year later, he found “[t]he trap had killed multiple sponges in that site. The reefs will not withstand that.”
Harley also agrees the government should boost enforcement of the fishing ban, as well as work in collaboration with local communities to reduce the need for illegal fishing.
“Coastal communities that depend on the ocean for food or for income may benefit from governmental help to change the way they fish or what they rely on for food,” he says.
The next domino to fall
While illegal fishing poses a direct physical threat to glass sponge reefs, Stevenson’s study shows how ocean warming and acidification imperil the reefs over the long term.
“The government needs to stop talking about climate action and actually implement the laws and policies they have formed, not in a couple of years, but now,” Stevenson says.
The urgency is real: Stevenson and her colleagues have already encountered water temperatures that surpass what they exposed the sponges to in the lab.
“As the world continues to change,” Harley says, “glass sponge reefs may be the next domino to fall.”
Citation:
Stevenson, A., Archer, S. K., Schultz, J. A., Dunham, A., Marliave, J. B., Martone, P., & Harley, C. D. G. (2020). Warming and acidification threaten glass sponge Aphrocallistes vastus pumping and reef formation. Scientific Reports, 10(1), 1-11. doi:10.1038/s41598-020-65220-9
