Glass Sponge Reefs: What are they?

“Glass sponge reefs are unlike anything else in the world. These fragile bioherms can reach 14 metres in height and cover a square kilometre, providing an important habitat for the fish that live in them. Until about 25 years ago, people believed that glass sponge reefs had gone extinct during the Jurassic period, but then they were discovered living in very deep water in Hecate Strait in northern British Columbia.” – Vancouver Aquarium 



What is a Glass Sponge Reef?

Glass sponge bioherms are rare reefs found only in Pacific Northwest waters. They are composed of sponges living on fossilized sponge skeletons (delicate silica or glass). They are extremely fragile and can break with even the slightest touch. Sponges are rare animals unlike any other in the world, as they do not have a digestive or nervous system and they can filter masses of water, producing nitrogen. The largest sponge reefs have been recorded to reach 12km long, and 8 stories high!

“Fossil records indicate that over the earth’s history sponge reefs have created the largest biological structures that have ever existed on planet, with some encompassing 4,300 square km, nearly double the size of the great barrier reef. These incredible structures were thought to have been extinct until 1986, when an oceanographic survey in the Queen Charlottes discovered a 9,000 year old sponge reef in Hectate straight that was 8 stories high and 700 square km.” – Marine Life Sanctuary Society (MLSS)

Compared to the discovery of dinosaurs, Glass sponge bioherms are a major ecological discovery for scientists. The only glass sponge reefs in the world are in Alaska and in BC. They have been recorded in Hecate Strait, Georgia Strait, Howe Sound and now in Chatham Sound (2016).

Divers exploring sponge reefs below 200ft

Tech divers Hamish Tweed and Chris Straub explore the Howe Sound sponge reefs to depths below 200ft. Photo by Diane Reid via No-Limits: Technical Diving Instruction


What does a Glass Sponge Reef do?

Scientists are still studying the sponge reefs to better understand their role in marine ecosystems. What they do know is that the reefs create a complex habitat on the sea floor for fish, crabs, and invertebrates by providing a nursery for reproduction. By pumping water through their bodies, they also act as a filter by removing bacteria and excrete ammonia – a source of nitrogen used by marine life in the area. 1 sponge can filter up to 9000L per day!


So why are we only hearing about them now? 

Glass sponge reefs live deeper than 250ft (76.2m) off BC’s coast. The deep depth combined with ocean conditions make these reefs nearly inaccessible. Only highly trained technical scuba divers, or submarines are able to reach these challenging depths.

Currently, Howe Sound has 10 glass sponge reefs on record, which the MLSS is actively working to map by drop-camera video. Trimix technical divers have now started exploring these reefs, making their 4th dive in May 2016.


Glass Sponge dive exploration in Howe Sound

Trimix technical divers Hamish Tweed and Chris Straub preparing to descend on their 4th exploration dive. Photo by Diane Reid.


The most recent major discovery has brought the sponge reefs forward into public light. In March 2016, a LNG company was conducting an environmental assessment in Chatham Sound, Prince Rupert. They found “ghost like images” rising 30m from the seabed. “The reef in Chatham Sound is twelve kilometres long, making it one of the largest in the world, second only to the prehistoric reefs in nearby Hecate Strait,” a rare ecological find for the world. Read more about the recent discovery here.

Understanding and protecting these unique reefs is of upmost importance, and the first step is public awareness. Now, when someone asks you what a glass sponge is you can give them all the answers!


Want to learn more? 

Vancouver Aquarium

Canadian Parks and Wilderness Society

Marine Life Sanctuaries Society



  1. There are multiple spots in Jervis and Sechelt inlets (Agamemnon wall and captain’s island wall among them) with extensive glass sponge reefs.

  2. Sea Dragon says:

    Thanks for the heads up! Thats great to know.

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