Deep Glass Sponge Reef

Diving the Deep: Glass Sponge Bioherms

Howe Sound is in Shearwater’s proverbial backyard. We regularly dive in it. Our friend and dive buddy, Hamish Tweed, tells us about a project he has been working on for a while. Note.- Click on the images in this blog post to see a higher resolution, more detailed version of the image.


One of the most common comments I get from people when they find out I’m a diver is that they don’t understand how I do it. I must not be claustrophobic, which I always found as a peculiar reason as to why people may avoid trying diving. This is not to say that, yes, the mask and equipment you wear can feel restrictive, but diving in the ocean is far from claustrophobic. Actually, it’s quite the opposite. It’s no secret that the ocean is vast and a mystery, where more than 80% of the ocean is unmapped, unobserved and unexplored. I think the more accurate phobia would be thalassophobia - an intense fear of the sea (or really any deep, dark body of water) and I can confidently say that I do not suffer from that.

I was lucky and found diving early in life at the age of twenty and I was hooked, it was truly all I wanted to do. By 1996 I was averaging over 300 dives a year and in 1998 I earned my IANTD Advanced Trimix Instructor certification. Since then I have been teaching advanced technical diving in British Columbia’s waters for my entire adult life.

From the beautiful top side scenery of the coastal mountains to the abundant list of species in our waters, British Columbia is truly a world class dive site. You can make the same dive on the same site on the same day and every dive will be very different, if you know how to slow down and look.

For the 20 years that I have been diving in Howe Sound, I know have only scratched the surface of dive sites. In 2012, I was approached by Glen Dennison, the then President of the Marine Life Sanctuary Society to see if I was interested in doing some exploratory deep technical dives in Howe Sound. Glen has spent well over 40 years diving, exploring and mapping the sound, so his knowledge of this body of water is humbly unsurpassed. I’ve had the pleasure and the good fortune to know Glen for over 20 years, so I knew there was something good that he had found in the depths.

Discovery of a living glass sponge reef


Within the local dive community, it was known that Glen had discovered and successfully identified two glass sponge reefs within the recreational limits for SCUBA divers (40m /120 ft range). Howe Sound is as far as we know currently the only place in the world where there is glass sponge in bioherms at waters as shallow as 40m or 125 ft.


The glass sponge reefs are referred to as bioherms. Meaning that as the sponge goes through its life cycle and naturally dies off the body of sponge breaks down while new life grows on top of the dead sponge, this is the new generation being born.

Through further exploration of mapping and scanning the sea floor Glen had also discovered additional glass sponge reefs spread across the tops of seamounts (some acres long in size) in deeper waters of 80m - 100m (250 ft - 330ft) that could be reached by technical mixed gas divers.

“Glass sponge? I’ve seen those sponges before on a dive”


Image credit: Lee Newman

Howe Sound is home to a number of different species of sponges, including siliceous sponges much like the cloud sponge we see at Whytecliff Park. Glass sponges are uniquely different, but to explain in scientific detail I will need many more letters behind my name.


Image credit: Hamish Tweed

While individual glass sponges (class hexactinellida) can be found on their own, but they receive little attention partly because they are inaccessible in their preferred deep depths of 450m to 900m (1,480ft to 2,950 ft). The existence of a glass sponge reef is considered extremely rare.

Glass sponges have distinct properties that make them unique to other sponges that we know of; from their electrophysiology and how they can conduct electrical signals to how they build reefs (or bioherms) by growing on the deceased structure of their ancestors.

The oldest record of a reef formation occurred over 220 million years ago and were thought to have gone extinct 40 million years ago. This means the glass sponge reefs would have lived in the prehistoric oceans for over 180 million years.

Scientific research is being conducted to determine the exact age of the sponges, but the current estimation is that the bioherm reefs of Howe Sound may be as old as 14,000 years.

It’s estimated that the animal can grow anywhere from 1 cm to 5 cm a year, depending on temperature and environment. Some of the larger individuals of animal we have observed were over 7 feet in height and could be anywhere from 100 to 400 years old, but at this point we still don’t know.

Diving the deep glass sponge reefs

The depth and lack of any visible daylight on these dives is only one of the challenges we face. Howe Sound is subjected to strong tidal exchanges throughout the year, so it’s not safe to dive on the sponge reefs during a strong tidal exchange (anything above 2 ft over a 6 hour exchange).

High tidal exchange vs Low tidal exchange

In certain parts of the year, Howe Sound can have unpredictable weather conditions where you can start a dive on a calm flat ocean and surface in gale force winds. In order for us to even have an attempt to complete the dive we need optimal tidal and weather conditions. If any one of these things is not the ideal, then the dive is called off.

I was more than eager to start exploring and documenting these reefs, but I couldn’t do it alone. I knew it would take careful planning to dive these deep sites as we were going to be the first people to ever visit these reefs. My first task was to assemble a team of experienced technical deep divers and experience technical safety divers. The safety divers are crucial for ensuring the bottom divers have the support they need getting into the water and in the event the bottom team members became separated or had a failure, the safety divers are there to provide assistance.

It takes a considerable effort over a number of months of planning and scheduling to find optimal conditions, diver and support team availability and because the team is comprised of volunteers we are typically limited to weekends. This means we only get a number of days in the entire year to have the opportunity dive the sponge.

First Dive – Lions Bay


Six months after our first meeting with Glen about exploring the sponge, we had a team ready and we made our first dive on the Lions Bay sea mount on February 23, 2013. That first dive consisted of just two bottom divers with a single Go Pro and housing that was only rated for 60 metres (200 feet). We were operating at 70 metres (230 feet) in total darkness with one homemade 10000 lumen video light and two smaller dive lights.


We had limited time on the bottom to film and capture images without over extending our decompression obligation, however we did manage to shoot and bring back about 15 min of very rough video that showed the size and health of the Lions Bay sea mount deep glass sponge reef.


Image credit: Chris Straub

Decompression Obligation

For every minute we are at our target depth on the bottom, we accrue about 3 minutes of decompression where we must stay in the water making multiple mandatory stops to allow the reduction of inert gases in the body. After spending 30 minutes on the bottom at 80 meters (250 feet), it takes our deep team about 100 minutes to slowly make the surface.

Our safety divers meet us at our 20 meter (70 ft) stop to accompany us for our last 7 decompression stops, which are the longest and most critical. They bring with them additional cylinders with decompression gas if needed and to communicate with the surface if a problem has arisen.


Image credits: Hamish Tweed

Later that spring the Vancouver Sun ran an article on our efforts to bring attention and the difficulties of diving the Deep Glass sponge.

The need for protection

For the last 5 years our team has been continually conducting dives and documenting on a number of the sites in Howe Sound. The video and images we have been capturing have been presented to Fisheries and Oceans of Canada (DFO) and interested stakeholders with the purpose of helping to gain protection status for these living reefs so that we and future generations can study the impact and role that play in our ecosystem.


It goes without saying that a sponge that is made entirely out of silica will be tremendously fragile. Not long after their discovery in Howe Sound it has become noticed that large areas of reef have been destroyed by bottom trawling, traps, and other harmful activities. So far Fisheries and Oceans Canada have implemented closures to formal fishing around nine glass sponge reefs in the Strait of Georgia and Howe Sound.<1>

The picture below shows damage most likely from prawn traps as there are being dragged when they are lifted off the bottom.

Image credit: Hamish Tweed

While we haven’t observed prawn traps on any of the sponge as of yet, however they are being deployed in the area of the reefs by those who probably just don’t understand what’s below them. It should be noted that many in the commercial prawn industry are cooperating by not trapping on the sites and for now it's the private boater out for a day on the water that still threatens the reef.


Image credit: Vanessa Heal

In addition to providing important deep-sea habitat for a host of species, from prawns to rockfish and sharks, it has also been identified that the reefs play a critical role in our ecosystem.

Water filtration

Sponges have an incredible power to filter vast amounts of water. How much is vast? Let’s take into consideration the already nine protected reefs and see how much water they can filter in ONE day. * With these reefs being in Canada, I’m going to apologize beforehand as these quantities will be in metric.

  • 1 square metre of reef can filter 25 - 45 cubic metres daily*
    • That’s an average of 8,750 jugs of milk!
  • 603,852 square meters of reef can filter 17 billion litres of water
    • That’s the equivalent of 6,500 Olympic sized swimming pools!
Promoting awareness


As divers we get to explore the subsea world and we are the ones that see first hand the wonders but also the devastation. If we can liken the sponges to a patch of old growth forests found in B.C., we’re hoping that we can help turn the tide of the apathy that the general public has to ocean conservation by capturing images of our world that most people cannot explore.


We’re actively promoting our exploration through community events, talks and social media. We continue to engage with as many people and groups as we can. Research and Education is the goal of our project.


What can you do:
  • Take a specialized course developed to teach safe diving practices around sponge reefs.
  • If boating or fishing in Howe Sound, familiarize yourself with the locations of sponge reefs that have been identified
  • Report illegal fishing and trappings to the authorities within the sponge closure areas.
  • Contribute to citizen science projects that are continuing to documenting the overall health of the reefs

As our 2018 dive season is underway and 2019 fast approaching, we are going to continue exploring the deep glass sponge reefs of Howe Sound and documenting the significance these animals have on our ocean. I would like to thank our contributors and sponsors, without their help our team would not have achieved these dives with this level of success over the last five years. Thank you very much for the continued support from everyone involved. This is truly a team effort.

What to look forward to in the coming year

Although our main goal is to study the sponge and document the reefs for interested stakeholders, we decided that we also want to take this opportunity to share with people the sheer amount of effort, time and resources it takes to dive these deep glass sponge reefs. In addition to sharing our experience through our social media pages, in 2017 we began to film and document the entire process of the project so we can give back to our community, contributors and sponsors who helped support this cause by showcasing their involvement in a web series to be released in 2019/2020.

Contributors & Sponsors
Marine Life Sanctuary Society Sea Dragon Charters
Underwater Council of British Columbia Light & Motion
Dive and Sea Sports Shearwater Research
New World Diving Charters
Dive Team
Diver Support
Hamish Tweed Glen Dennison
Chris Straub Adam Taylor
Rene Gauthier Vanessa Heal
Nikita Sergeenko Marc Jean Palay
Amy Young Kevin Brekman
Andy Wiggs Jan Brekman

Jessica Schultz (Manager of Howe Sound Research and Conservation Vancouver Aquarium)
Glen Dennison (Marine Life Sanctuary Society)
Sally Leys (Professor of Biological Sciences University of Alberta)


Underwater Council of British Columbia: