Sea urchins are easy to recognize for their “pin-cushion” of spines. They are hard-shelled echinoderms (marine invertebrates with tube feet and five-part radially symmetrical bodies) that crawl along the seabed or onto seaweeds with their tube feet. In Howe Sound, the red sea urchin (Strongylocentrotus franciscanus) can be found together with the smaller green urchin (Strongylocentrotus droebachiensis). Both in Howe Sound and on outer coasts, the red urchin (shown at the top) is the largest of our B.C. sea urchins, and it has the longest spines.
The blog post on echinoderms showed a Howe Sound urchin barren (an overgrazed area) consisting of thousands of green sea urchins (see photo on left). These green urchins have very fine, short spines and are common in areas away from wave surges.
Green urchins undergo population explosions, after which the urchins keep all the seaweeds grazed down to virtually nothing for periods of years. The wolf-eel is one predator that thrives where there is an urchin barren, munching down on the urchins –spines, shell and all.
The third most common B.C. urchin species, the purple sea urchin, with its short, heavy spines, never lives in Howe Sound because there is no crashing, outer coast surf, and that is the type of habitat in which purple urchins thrive.
With the support of Sitka Foundation, the Vancouver Aquarium is embarking on a two-year project to train divers to identify marine life in Howe Sound, as part of our commitment to the research and conservation of this area. The information they glean on Howe Sound’s sea life will be presented in this series of blogs, and will be used to educate students taking part in the Aquarium’s school programs and AquaVan visits to inspire the next generation to keep learning more about marine biodiversity in British Columbia.