Studying the globally unique glass sponge reefs

By Amanda Kahn

[Cross-posted on the Students Ensuring our Oceans’ Future blog.]

One month ago, we were busy in the lab at the University of Alberta preparing and calibrating instruments, gathering GPS waypoints, and preparing dive plans. Three weeks ago, we drove and flew to Vancouver Island with our equipment and plans. Two weeks ago, we boarded a ship to study the glass sponge reefs in the Strait of Georgia in B.C.

CCGS Vector

Heading out on CCGS Vector, our home away from home. Credit: A Kahn 2013

The main reef we were studying on this trip was on Fraser Ridge. If you drained the water from the SoG, you’d be able to see the ridge and the reef about 14 km away from Vancouver. Fraser Ridge reef is too deep for us to study directly by scuba (150 to 180 meters deep), so instead we study it with the help of the remotely operated vehicle (ROV) ROPOS. ROPOS is piloted and run by the Canadian Scientific Submersible Facility (CSSF) and functions as our eyes and hands underwater.


ROPOS, our eyes and hands underwater. Credit: A Kahn 2013

With those eyes and hands, we studied the energy use and water pumping capacity of the glass sponges that build the reef. Glass sponges are really amazing animals—they can move huge amounts of water through their bodies, which are basically modified to be amazing filters. 9,000 liters of water can pass through a single sponge osculum (the “chimney” that water is released from by the sponge) each day! And from that, the glass sponges can feed on tiny particles, especially bacteria. This is pretty unique among animals—most other animals that feed on particles suspended in the water (called “suspension feeders”) can only capture particles that are larger by 10 times or more.  We did a lot of great science while on board the ship, and I’m now at the field station in Bamfield, British Columbia, to work with other sponges.  We will all spend the winter back in Edmonton working up the samples and data collected from this trip.

Glass sponge reef

Glass sponges in a reef–check out all of those oscula! Credit: CSSF 2011

I’m happy to be a part of SEOF because I can feel connected to other folks who are near the ocean full-time, can ask questions about logistics before I arrive, etc.  I’m the regional representative for Alberta and in this post wanted to show that being far from the ocean does not mean that we cannot have access to marine animals or study ocean-related issues.  Logistics may be more tricky than driving down to beach for the weekend to do some intertidal sampling, but it’s definitely doable and totally worthwhile.  Contact me if you have questions about the reefs or if you’re in Alberta and have questions about how you can get involved in the marine science community across Canada.

To learn more about the reefs, check out these videos, compiled by Sameena Sherman, a student from our lab:

Getting to the heart of urchin spine attachment

Amanda loves tide poolsby Amanda Kahn

One of the really neat things about BMSC is that it’s got a lot of resources on-site for us to use.  A freeze drier, autoclave, fume hoods, field equipment, scientific diving program, drying ovens, distilled water, wet labs, dry labs, and so much more fill the buildings of the research station, allowing so many cool and interesting projects to happen.  However, since Bamfield is remote and doesn’t have the same infrastructure as our home universities, many of us take our samples back to our home campuses to use more energy-intensive or specialized equipment there.

During a course at the University of Alberta that specialized in microscopical techniques and advanced invertebrate zoology, I studied an irregular, or heart, urchin that had been collected from BMSC.  Unlike most sea urchins, which have conspicuously long spines projecting from a round, pentaradially symmetrical body (pentaradial means there are five planes of symmetry through an animal), heart urchins do not show pentaradial symmetry.  Instead, they have a mouth on one end of their body and they burrow through sediments in a definite direction (namely, forwards), extracting edible organic bits from the inorganic mud of the seafloor.  Both types of urchins–regular and irregular–use spines on the downward-facing (ventral) side of their body as paddles or stilts to move around.

The heart urchin in the video above, Echinocrepis rostrata, looks like a giant nose sniffling around the seafloor.  Others look like ovals, but all have a side that’s primarily for pushing through the sediments and another side that is not.  For my class project, I used scanning electron microscopy to compare the attachment sites for spines on the downward-facing (ventral) side, which pushes through the mud, with those on the upward-facing (dorsal) side, to see if all that paddling through the sediments makes a difference for the ventral side.

Heart urchin spine

Credit: A Kahn

Heart urchin close-up of spine base

SEM image. Close-up of the base, showing the milled ring (MR) and central ligament (CL) attachment site. Credit: A Kahn

Above are two SEM images of an urchin spine, taken at the Advanced Microscopy Facility at the University of Alberta.  At the base, there’s a milled ring (MR), which muscles and the central ligament (CL) attach to.  Those muscles and ligaments then attach to tubercles and attachment sites on the skeleton (called a “test”) of the urchin.

Heart urchin - dorsal side, with ossicle sutures

View of the dorsal side of the heart urchin. Those round peaks are the attachment sites for the spines. AD – adradial sutures, connecting different plates of the urchin test together. Credit: A Kahn

Above now is a picture of attachment sites on the dorsal, non-burrowing side of the heart urchin. Notice that they’re circular, and that, according to the scale bar in the upper right, each attachment site on the dorsal side has a diameter of 200 microns or less.  Now check out the attachment site from the ventral (downward-facing) side of the urchin in the SEM image below–the attachment sites are no longer circular, but ovoid, and they are HUGE!  Much longer than 200 microns along the widest axis!

Ventral side

CL – central ligament. T – tubercle.  ta – tendon attachment.  ST – stereom trabecula…a fancy name for the porous-looking part of the urchin’s skeleton. Credit: A Kahn

I wondered why this was, and I hypothesized that since spines on the ventral side are the ones responsible for the urchin to zip (err, relatively speaking) through the mud, they need to have more, or stronger, muscles, that would require bigger attachment sites.  Heart urchins have a front end and a back end they move primarily in one direction, so the attachment sites might be ovoid because the spines move mainly in one direction and they’d need more muscles for that direction of movement.  It’s all hypotheses at the moment–to actually see if that’s the case, I’d have to study more than just an urchin test, and actually observe live urchins, look at the muscles that are attached and how strong they are…sounds like another trip out to Bamfield!  Still, it’s a neat idea.

Do you have other ideas for why the attachment sites are so much larger on the ventral versus the dorsal side?  Or why they’re shaped like ovals?  How would you go about testing your hypothesis?  Let’s brainstorm in the comments below.