Any ocean research and surveyance crew heading into the sea hopes to make exciting discoveries. For those at the Geological Survey of Canada in the 1980s, their trips were no different. “Our objective was to map and understand submarine geo-hazards that posed a risk to coastal populations and seabed infrastructure, provide an interpretation of Quaternary marine geoscience, including present-day issues such as sea level, and map benthic habitat,” says Dr Vaughn Barrie, now Emeritus Research Scientist at the Geological Survey of Canada at the Institute of Ocean Sciences.
When the side-scan sonar first picked up unexpected mound features in the Hecate Strait and Queen Charlotte Sound, which runs along the west coast of Canada, nobody expected them to be ancient yet living glass sponge reefs, especially since reef-building glass sponges were thought to have gone extinct during the Cretaceous period.
Glass sponges, or to give them their formal name, Hexactinellids, turn dissolved silica in the seawater into long shards called spicules from which they build intricate and captivating skeletons. “The first [glass] sponge I saw was a boot sponge [Rhabdocalyptus dawsoni], beautifully white inside and completely mucky on the outside – a stubby tube hanging out from a cliff at about 100 feet [30 meters]. Everything else there is dark and small, so it definitely captivated me,” says Dr Sally Leys, who has since become a leading sponge expert at the University of Alberta.
Glass sponges come in two flavours – those with spicules that are loosely placed, held together by tissue, and a special group that can fuse those spicules together secondarily to form a rigid 3D structure. Leys boot sponge has loose spicules. In a few locations where the water is particularly cold, such as in Antarctica, in some submarine caves in the Mediterranean, the fjords of New Zealand, and the waters of British Columbia, Canada (where Leys boot sponge was), they live in relatively shallow depths. Most, however, live in depths of 500 metres or more.
The species that form reefs, like the cloud sponge Aphrocallistes vastus, settle on other individuals and fuse to them, creating large, robust, three-dimensional structures. “When I dove on cloud sponges, they were more awesome. You knew you would encounter them at about 100 feet (30 meters) or deeper, so your eyes scoured the depths as you slowly dropped until Boom! there they were in front of you, a billowy yellowness,” explains Leys.
When a reef-building sponge dies, other sponges will fuse to and grow on the skeleton left behind. An individual sponge can reach heights of one and a half metres over its 200-year life. Collectively, the reef can reach heights of over twenty metres.
Multiple surveys lead to the discovery
Seabed mapping technology in the 80s was quite different than it is today. “There was no multibeam sonar, no GPS, and limited digital technology,” explains Barrie. Alongside other factors such as expedition track, perhaps it is unsurprising that the “discovery of glass sponge reefs was not an instantaneous event,” explains Barrie. “The first geophysical survey that passed over the sponge reefs occurred during one the earliest exploratory scientific surveys as part of the research ship Hudson’s circumnavigation of the North America [which ran from 1980 to 1981],” says Barrie.
It wasn’t until a major survey in the late 80s that the secrets of the reefs revealed themselves to Barrie and his colleagues, Dr Kim Conway and Dr John Luternauer. “At this point, we were aware of these curious mound features and determined to identify them,” says Barrie. “Using sub-bottom profiling, side-scan sonar, sediment cores, and bottom photography, Dr Kim Conway made the bold interpretation of what these features [glass sponge reefs] were on the ship and was proven to be correct.”
The discovery made waves in the scientific community. “At first, I couldn’t believe it. We thought that glass sponge reefs had gone extinct about 40 million years ago, and then all of a sudden, here is this ancient ecosystem alive and well off the coast of Canada,” Dr Manfred Krautter, a paleoecologist who was based at the University of Stuttgart (Germany), told the Canadian Parks and Wilderness Society, who have been at the forefront of campaigns to give the reefs greater protection. Before the discovery in Canada, Krautter’s study of glass sponge reefs was limited to fossilised remains. His expertise was essential in confirming that the Canadian researchers had found “a living dinosaur,” says Barrie. In 1999, Krautter joined Conway, Barrie, and colleagues for a research trip that included submersible dives – the “first direct human observation of a reef type that was widespread during the Age of Dinosaurs,” as Conway wrote in their paper published in Geoscience Canada in 2001.
Unique systems under threat
Since those surveys in the 1980s, the glass sponge reefs have become the focus of much scientific attention. Four glass sponge reefs have been confirmed in Hecate Strait and Queen Charlotte Sound, covering a combined area of 1,000 square kilometres. The largest reef is 35 kilometres long, 15 kilometres wide, and 25 meters high. Radiocarbon dating suggests the reefs started forming some 9,000 years ago. A few other smaller reefs have since been located further south in the Strait of Georgia and Howe Sound in Canada, in Washington State, USA, and further north in southeast Alaska, USA.
These “glass sponge reefs are unique because they are only found in the Northeast Pacific,” says Leys. “That’s unusual indeed, and it says a lot about the very precise conditions that they need to build reef structures.” Studies suggest those conditions are a combination of cold temperatures (between nine and ten degrees Celsius), low light, low sediment loads, high levels of dissolved silicate, and a hard substrate, primarily the skeletons of other sponges, to grow on. We also know that the reefs are critical habitats for many other marine species, including commercially fished species that use the reefs as a nursery ground. As filter feeders, when they pump water through their bodies to extract the bacteria they like to feast on, they also clean the water.
However, much of their biology and ecology remains a mystery. “Not a lot of people study the biology of glass sponges because they’re deep [dwelling] and hard to keep in tanks,” Leys explains. Among the mysteries Leys would love to solve are those around action potentials, electrical signals that allow the different cells in sponges to communicate with each other and coordinate their activities. In the absence of a brain or nervous system, action potentials that run through the unique syncytial tissues allow glass sponges to react quickly to changing conditions. For example, if there is a lot of sediment in the water, they will stop pumping water so they don’t become clogged. “I think understanding how the action potential works will allow a better appreciation of the sensitivity of these animals to disturbances,” Leys explains. “They’re picky, liking a little sediment to cement things together. Not a lot, though, as it makes them ‘cough’,” Leys offers as an example.
Indeed, the glass sponge reefs are fragile ecosystems. Research from Leys lab has shown how sediment plumes created by human activities, like bottom trawling, can stop the sponges feeding, even if that activity occurs several kilometres away. Arguably, the most significant threats take place much closer to the reefs. When Leys and colleagues took a remotely operated submersible (ROV) down to the reef-building cloud sponge Aphrocallistes vastus, the team had “time to absorb how delicate [the sponge’s] tops are that waft in the wash of the ROVs propellers.”
Sadly, the side-scan sonar taken from Barrie, Conway, and Krautter’s 1999 research trip found clear evidence of threats to these delicate animals; abundant bottom trawl fishing tracks and “areas of sponges lying broken off at the seafloor.” At one site, they also found “a linear ridge or berm of sponge skeletal debris to a height of approximately 40 centimetres.” The scientists concluded that this ridge “probably represents a ploughed reef surface where the skeletal remains of sponges have been piled up by mobile fishing gear.” Since the reefs are slow-growing, recovery could take hundreds or even thousands of years.
Protection for the Hecate Strait and Queen Charlotte Sound reefs
The reefs are no longer hidden beneath the sea’s surface, which means how people interact with the reefs has changed. In 1999, Fisheries and Oceans Canada asked groundfish trawlers to avoid the reefs. By 2002, the voluntary scheme became a regulated closure, with shrimp trawlers also asked to voluntarily avoid the reef areas to avoid catching the sponges from above. Four years later, in 2006, fishing gear restrictions became stricter. A buffer zone around the restricted area was also created to provide additional protection.
However, it isn’t just fishing activity that can damage the delicate sponges or create sediment plumes that can smother them. Other threats include cable laying, oil and gas extraction, and anchoring. It took another decade of campaigning before the Hecate Strait and Queen Charlotte Sound reefs formally received marine protected area status. This higher level of protection includes an adaptive management zone running out along the sea floor and a vertical adaptive management zone to tackle threats from the waters above the reef.
As of May 2023, the other glass sponge reefs in Canadian waters are protected by marine refuges – fishery closures designed to protect species and ecosystems from fishing activity only. Organisations like the Canadian Parks and Wilderness Society would like to see these reefs have marine protected area status too. As for the Hecate Strait and Queen Charlotte Sound reefs, given that sediment plumes originating kilometres away can impact the sponges, Leys says the protected areas need to be larger. “The boundaries…were set before the science was done, but [they] have not been changed after the science showed they are too small by far,” Leys explains.
Seabed mapping was the first step in bringing these reefs into the light, improving our understanding of these delicate, ancient systems, and putting protection in place, even if that protection is not perfect. Now, as we explore other less well-mapped parts of the ocean, we could very well find other equally important jewels hidden beneath the waves.