Far beneath the cold waters off British Columbia, an extraordinary ecosystem is thriving in near-total darkness, a vast network of reefs made not from tropical coral, but from animals whose skeletons are built from silica, the same material found in glass.These are glass sponge reefs, and for decades scientists believed reef-building sponges of this kind had disappeared from Earth roughly 40 million years ago.Then, in 1987, Canadian scientists discovered that they were still alive.According to Fisheries and Oceans Canada (DFO), four major glass sponge reefs were discovered that year in Hecate Strait and were found to be more than 9,000 years old. The discovery revealed that an ecosystem once thought extinct had survived in the deep waters off Canada’s Pacific coast.Today, these extraordinary formations are often described as the “Sea of Glass.”
Reefs built by animals, not coral
Glass sponges are marine animals whose intricate skeletons are made from silica. Unlike the soft-bodied sponges familiar from shallow waters, these deep-sea animals create rigid, glass-like structures.Some species are capable of building reefs. New generations of sponges settle on the skeletons left behind by previous generations, gradually creating enormous mounds and ridges on the seafloor.DFO says the reefs can grow to hundreds of square kilometres and reach heights of up to 25 metres. The largest reefs in Hecate Strait and Queen Charlotte Sound lie between about 140 and 240 metres below the surface.The four major Hecate Strait reefs cover an area of about 1,000 square kilometres and are considered the largest living examples of glass sponge reefs that were once widespread during the Jurassic period.
A prehistoric ecosystem that survived
Glass sponge reefs were discovered alive in Hecate Strait in 1987 after being thought extinct for 40 million years. (Photo: DFO, Sally Leys, University of Alberta, CSSF ROPOS)
The story of these reefs goes back hundreds of millions of years.Glass sponge reefs were once common around the world, particularly during the Jurassic period. Fossil evidence shows that they formed extensive reef systems long before modern coral reefs dominated many marine environments.Scientists believed living reef-building glass sponges had disappeared approximately 40 million years ago.That assumption was overturned when Canadian scientists mapped the seafloor off British Columbia in the 1980s.Natural Resources Canada scientist Kim Conway, who was involved in the expeditions, recalled that researchers initially encountered unusual mounds and ridges without immediately understanding what they were. It took several expeditions and years of investigation before scientists determined that the formations were reefs created by sponges.The discovery was formally confirmed in 1987.
Why these reefs exist off British Columbia
Glass sponges can be found in oceans around the world, but the enormous reef formations are exceptionally rare.According to DFO, British Columbia’s glass sponge reefs occur in Hecate Strait, Queen Charlotte Sound, the Strait of Georgia and Howe Sound. Most are found at depths between about 90 and 300 metres, although some reefs in Howe Sound occur much closer to the surface.The reefs require a particular combination of environmental conditions, including cold, nutrient-rich water and sufficient dissolved silica for the sponges to build their skeletons.These conditions have allowed the animals to survive and build reef structures over thousands of years.
A giant filtration system beneath the Pacific
The 9,000-year-old reefs survive today in Hecate Strait, Queen Charlotte Sound and Howe Sound. (Photo: DFO, Sally Leys, University of Alberta, CSSF ROPOS)
The reefs are not simply remnants of prehistoric life. They are functioning ecosystems that continue to play an important role in the modern ocean.Glass sponges pump seawater through their bodies and filter microscopic organisms and particles from the water.Their enormous reef structures also provide shelter, refuge and nursery grounds for marine species, including rockfish, finfish and shellfish. DFO describes the reefs as important habitat for numerous aquatic species.The intricate structures effectively transform sections of the deep seafloor into complex underwater habitats, creating an oasis of marine life in otherwise relatively flat areas of the Pacific.
Thousands of years to build, but easily damaged
The extraordinary age of these reefs also makes them extremely vulnerable.Their skeletons are made of silica and can be broken by physical contact. DFO warns that fishing gear and other activities that disturb the seafloor can damage the structures, while increased sediment can smother the sponges and interfere with their ability to survive.Recovery is exceptionally slow.DFO notes that individual glass sponges can live for more than 200 years, while recovery from significant reef damage could take tens to several hundreds of years. If the skeletons of dead sponges are destroyed or buried, new generations cannot use them as the foundation for further reef growth.Climate change is adding another concern, with scientists investigating how warming and changing ocean chemistry could affect the fragile organisms and the ecosystems they support.
Canada created a marine protected area
The discovery eventually led to major conservation measures.In 2017, Fisheries and Oceans Canada designated the Hecate Strait and Queen Charlotte Sound Glass Sponge Reefs as a Marine Protected Area.The protected area covers approximately 2,410 square kilometres and was created to conserve the biological diversity, structural habitat and ecosystem functions associated with the ancient reefs.The reefs are also on Canada’s Tentative List for potential UNESCO World Heritage recognition because of their geological, biological and paleontological importance. Parks Canada describes them as a unique window into prehistoric marine ecosystems.
One place where divers can see them
Most of British Columbia’s glass sponge reefs remain far too deep for recreational divers.But Howe Sound offers a remarkable exception.According to DFO, glass sponge reefs in Howe Sound can occur at depths of just 22 metres.At Halkett Point near Gambier Island, the reef lies in approximately 30 metres of water, making it one of the few places in the world where glass sponge reefs are accessible to both scientists and scuba divers. BC Parks says the marine area was specifically expanded in 2016 to protect the rare reef.For non-divers, conservation organisations have created educational resources and digital maps that allow people to explore the “Sea of Glass” without descending into the deep.
A prehistoric world still alive
The glass sponge reefs of British Columbia are remarkable precisely because they are not fossils.They are living ecosystems, descendants of a reef-building lineage that flourished when dinosaurs roamed the planet.For millions of years, scientists believed these reefs had disappeared. Their discovery in 1987 proved otherwise, revealing a hidden world that had continued growing in the darkness of the Pacific.Today, the “Sea of Glass” is both a scientific wonder and a conservation priority, an ancient ecosystem that survived for thousands of years, yet remains vulnerable to damage in a rapidly changing ocean.
