Anybody who gets the chance to dive around cloud sponges, especially on Howe Sound’s unique shallow glass sponge reefs, will be charmed by the otherworldly beauty of these most primitive life forms. The reefs had been thought to have gone extinct in the Jurassic, and now are known only in B.C. This province’s glass sponge reefs apparently consume 230 tonnes of bacterial carbon every day. These living seabeds, when healthy, are teeming with a variety of marine life – fish, crabs and shrimp, including B.C.’s beloved spot prawns. I was part of the Vancouver Aquarium Marine Science Centre dive team that discovered a diveable sponge reef near Howe Sound’s Defence Island in 2005.
Back then, the diving community had adopted a code of secrecy to keep these rare formations safe from accidental damage. The thinking was that if people didn’t know about these reefs they wouldn’t attract attention and increase the risk of harm from human activity. In reality, the opposite was true. We now know that prawn trapping and salmon sport trolling do too much damage to these reefs to ignore, and we’re working to increase public awareness of the fragile life forms. Keeping them alive and thriving is crucial to maintaining vital marine habitat.
But there appears to be another factor contributing to sponge reef mortality. Starting in 2009, the Aquarium team began investigating how climate patterns affect these reefs when we noticed a die-back of tissue during the strong 2009-2010 El Niño. It seems like warm weather events can directly cause sponge mortality, and may exacerbate the impact of mechanical damage, so that when the two occur simultaneously reef tissue appears to die more rapidly.
On the other hand, we’ve seen some of this tissue recover during La Niña events when the weather is cooler. We suspect the colder weather is less stressful on the physiology of the shallowest cloud sponges so they can recover more readily from mechanical damage. The cumulative impact of climate events and human-caused damage is something we’re continuing to monitor in the 2015-2016 El Niño year thanks to a grant from the Environmental Damages Fund of Environment Canada. In the process, we’ve noticed something remarkable about these prehistoric sponges: given the right conditions, they’re practically immortal.
In other types of glass sponges, such as the boot sponge, we see senescence – the breakdown of tissue due to age – appear in about a decade. The first signs of senescence are disorganized tissue, irregular body form then the appearance of holes and rips. Finally, the sponge biodegrades and is gone. Something comparable occurs with cloud sponges living on rock, in sponge gardens.
Not so with the cloud sponges we find living as part of reefs in Howe Sound. Parts do disintegrate, causing some tissue to topple, but parts that land in a stable position on the reef may start to regrow. It’s sort of like losing your hand and then having it regenerate into a new intact body. To learn more about this occurrence, I’ve been doing some transplanting experiments (using EDF funding) in Howe Sound to see when and how this new growth occurs. The video below shows me relocating a large sponge that had toppled upside-down. I’m propping it up against dead tissue to see if it will attach and regenerate.
The current El Niño system seems to be causing some major toppling of large, old sponges that become imbalanced as old, dead tissue deteriorates at the base of a sponge while growth continues on top. In addition to propping up fallen sponges, I’ve been grafting live tissue onto live and dead sponge heads to see how quickly they reattach. What we learn here could tell us more about the recovery potential of this integral species, and eventually help set policy to protect it from accidental damage. Stay tuned for more updates as we learn more.
Blog post by Dr. Jeff Marliave, vice president of marine science at Vancouver Aquarium Marine Science Centre. Learn more about the hidden gems in Howe Sound during our Divers’ Weekend Jan. 16-17, 2016.