Glass Sponge Reefs
Once thought to have gone extinct millions of years ago, in 1989, the first ever living glass sponge reef was found in Hecate Strait, near the Haida Gwaii. Then, in 2001, after glassy shards were found washing ashore on Galiano Island, the reefs were found to be growing at several locations in the Strait of Georgia. These “living fossils” are the only discovered glass sponge reefs in the world, and are the subject of much recent research. The sponges, which are extremely slow growing, provide shelter and habitat for many bottom dwelling animals that would otherwise be unable to live on the barren deep-sea floor.
Location and AccessCoordinates: 48°55’N 123°17’W / 49°14’N 123°48’W / 49°22’N 124°17’W / 49°25’N 123°45’W / 49°05’N 123°20’W
There are five discrete reef clusters in the Strait of Georgia. They are located off the east coast of Galiano Island, about halfway betweenValdez Island and Richmond, off the northeast tip of Gabriola Island, between Parksville and Lasqueti Island, and the largest, just off the mainland coast between Sechelt and Gibsons.
All of the reefs are located between 90m and 290m in depth, beyond the limits of traditional SCUBA diving, and require sophisticated equipment to visit. Several different teams have utilized the Vancouver built scientific submersible ROPOS (remotely operated platform for ocean science) to explore the reefs, providing scientific data on the sponges’ habitat as well as high quality underwater photo and video.
Not much is known about how a sponge reef begins to form, though it is clear that they need a site that is deep, cold, and relatively free of active sedimentation. As filter feeders, they also need a considerable amount of turnover, and as such tend to colonize areas with a plenty of water movement. There are seven varieties of sponges on the reefs, three of which do the building (the finger goblet sponge, the cloud sponge, and Farrea occa). These sponges incorporate silica from the water into their bodies, and over hundreds of years, the glass skeletons can reach 14m in height. Overall in BC, the sponges cover a combined area of 700km2.
Life on the reefs:
The sponges themselves comprise seven members of the Hexactinellida class of sponges, all of which incorporate four or six pointed silica fragments into their bodies in order to support growth. They filter food from their surroundings by passing water through tiny openings in their tissue and retaining the food particles and edible bacteria. Their ability to colonize barren ocean floor is important to the benthic ecosystem, as the sponges will provide the habitat heterogeneity needed by other animals, and can single-handedly provide a thriving reef where no animal would otherwise. Several studies have shown squat lobsters, anemones, small crustaceans, nudibranchs, lingcod, seastars, and varieties of rockfish making the reefs home. One study in particular documented a tenfold increase in rockfish densities in the area of the sponge reef, an important effect given the pressure on the rockfish populations in the area. The reefs act as a nursery of sorts for the fish, providing a place free of large predators in which to spend the first few years of their lives.
Studies have also documented the role of living sponges in the formation of these communities, noting that damaged or dead sponge reefs are typically much less active in terms of local life. This killing of the reefs is primarily due to bottom trawling for many of the species that live on the reefs, and when researchers first discovered the reefs, they documented trawl marks, and kilometers of freshly destroyed reef in the trawl area. Environmental groups lobbied for protection, and the government complied, reserving areas as trawl-free zones, however it is estimated that many more reefs could still exist undiscovered, and any trawl activity in their area could be continuing to destroy this rich habitat.