Living Glass

By Katie Gerstle |

We have a lot of beautiful biodiversity in the Pacific Northwest, but one of the most startling features of this coast are its living glass structures – yes, LIVING animals made of glass. And if you're a diver, you've likely seen them.

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Cloud sponges (such as Aphrocallistes vastus) are just one species from the unique class of glass sponges (Hexactinellida) that are a common sight in our chilly BC waters. Glass sponges can live between 16 – 650m deep in coastal Canadian waters, but but can be found as deep as 3000m worldwide! Glass sponges thrive in conditions with little to almost no light, consistently cold temperatures (9 – 10°C), and an abundance of silica to repair and grow their fragile skeletal structures.

Hexactinellid class sponges and the reefs that they form are unique to the Pacific Northwest, and represent about 600 species of sponges that produce skeletons composed of almost pure glass. Who knew that there were so many kinds of sponges? In Howe Sound, glass sponges are found incorporated into sponge gardens as colonies of individual cloud sponges (such as A. vastus, an ancient species of glass sponge found in abundance in Howe Sound). We also find them in bioherms, or vast reefs composed entirely of different species of glass sponges (such as A. vastus, Farrea occa and Heterochone calyx).

We don’t know for sure, but they’re thought to be very long-lived animals (yes, sponges are in fact a part of the animal kingdom, in the phyla ‘Porifera’) that feed on bacteria and dissolved organic matter. From what we know, the special canals that some sponges use to take in their food can be easily clogged in areas with heavy sediment and particulate matter. Our local diving hotspot, Howe Sound, is a very sediment-rich environment due to organic matter and deposits carried over from the Fraser River into the Strait of Georgia, the rivers flowing into the Sound’s north end, and a history of local industrial activity. But we still see lots of cloud sponges at Whytecliff, Hut Island, and Boyer Island, to name just a few – so how does that work?

Many of the glass sponge reefs documented in Howe Sound are on the leeward side of an underwater sill, a shallow section of the seabed, located just north of Anvil Island. As sediment-rich water heads downstream from the rivers in Squamish, it increases in velocity at the crest of the sill, sending the particulates far over the edge of the sill, and giving the leeward section of the sill, with its precious cloud sponge reefs, some shelter from sediment buildup. The waters south of the sill are typically much clearer, since they do not get the bathtub-like effect that water trapped north of the sill is exposed to. However, it is believed that many other Howe Sound reefs may exist, but they’ve been long buried by sediment buildup over time.

Glass sponge reefs play a unique role in deep water ecosystems, such as elaborate three-dimensional shelters for fish, crustaceans, one species of nudibranch (Peltodoris lentiginosa), warbonnets, and squat lobsters. As they filter their food out of the environment, they also steadily extract carbon and remove of 75-90% of the bacteria found in the surrounding water. In fact, one square meter of glass sponge reef cleans and filters 165 square meters of water every day; that’s the equivalent of a sponge roughly the size of the surface area of your coffee table being responsible for cleaning about half the size of an IMAX movie screen in ocean water. And just to top it all off, the extraction and filtration process releases small amounts of ammonia into the water column above the reef, which can be transported through currents to fuel organic productivity elsewhere in the ocean!

As divers, we’re taught to look and don’t touch; take only pictures, leave only bubbles. This lesson couldn’t be more important when it comes to the fragility of these sponges. I have personally seen sponge fragments littering the edge of a wall at some of our local dive sites. A careless fin kick here and there builds up, and we start to lose more and more of these deep water purifiers. Mass remnants of broken sponges lining sections of the seabed are a typical indicator of bottom trawling, a destructive fishing method for marine habitats, that has been seen at the mouth of Howe Sound and elsewhere in the Strait of Georgia. In addition to bottom trawling, glass sponges have readily appeared in bycatch records since 1996, meaning that they’ve accidentally been swept up in fishing gear. Divers may not have the largest direct physical impact on these reefs when compared to commercial operations, but we can sure make our time underwater count. How? Buoyancy. Continually practicing and improving one’s buoyancy skills helps conserve air, lengthening bottom time, and allows us to fine-tune every movement underwater with precise control. Then, we have the capability and the confidence to get closer to some amazing sponges and the critters that call these living chandeliers home.

For more information on how you can help protect glass sponge reefs, read up on how CPAWS (Canadian Parks And Wilderness Society) is trying to establish marine protected areas where these reefs are located. Also, check out our PADI Peak Performance Buoyancy course if you’re looking to improve your skills!



Sources:

Chu, J. W., & Leys, S. P. (2010). High resolution mapping of community structure in three glass
sponge reefs (Porifera, Hexactinellida). Marine Ecology Progress Series, 417, 97-113.

Leys, S. P., Wilson, K., Holeton, C., Reiswig, H. M., Austin, W. C., & Tunnicliffe, V. (2004).
Patterns of glass sponge (Porifera, Hexactinellida) distribution in coastal waters of British
Columbia, Canada. Marine Ecology Progress Series, 283, 133-149.

Kahn, A. S., Yahel, G., Chu, J. W., Tunnicliffe, V., & Leys, S. P. (2015). Benthic grazing and
carbon sequestration by deep-water glass sponge reefs. Limnology and Oceanography, 60(1),
78-88.

Marliave, J., & Challenger, W. (2009). Monitoring and evaluating rockfish conservation areas in
British Columbia. Canadian Journal of Fisheries and Aquatic Sciences, 66(6), 995-1006.