by Amanda Kahn
My first SCUBA dive in Bamfield was at a site called “Aguilar”, although by some it’s also called the “Love Shack.” I don’t know the history of the building that sits perched on the rocky intertidal zone in the cove (maybe a local can chime in on that in the comments below), but the picturesque cove is an interesting, curiosity-inspiring place above- and below-water.
A dive beneath the Love Shack features reveals a shallow field of cobbles housing sea squirts, sponges, snails, sea stars, and TONS of sea urchins. Aguilar sits at the northeastern tip of Bamfield’s West Side, which means that from the marine station, it is accessible only by boat. It is a good site for a training/practice dive, which is what we used it for, because it is protected from swells (it was a stormy day the day we dove), shallow, and there are open expanses on the seafloor where one can practice skills without quite as much worry about bumping into a fragile animal (though buoyancy control should never be undervalued).
This site is an urchin barren, meaning if you go, you’ll find a habitat that’s overrun with urchins. Urchins are often opportunistic feeders who sit in burrows and feed on kelp that happens to drift by. However, urchins in urchin barrens come out of their burrows and scour the benthos (seafloor), eating through live kelps. What results is a habitat that contains mostly urchins, and very few kelps. Pictured in the video below is an urchin barren filmed near BMSC.
Farther south, studies have shown that the loss of one of urchins’ key predators, sea otters, is implicated in facilitating the swap from a kelp forest habitat to one of an urchin barren. Whatever causes urchin barrens up here, once a habitat becomes an urchin barren it is fairly stable–it would be difficult to recover the habitat back to a kelp forest. Likewise, if a kelp forest is robust and healthy, it is difficult to convert it into an urchin barren. In the video below, notice that there are tons of urchins visible, but no kelp in sight.
This interesting phenomenon is called “alternate steady states” by ecologists.and is interesting because it shows that no one habitat is the best for a specific location. Can you think of other habitats, whether in land or in the water, where there can be alternate steady states? The urchin barren/kelp forest is the classic example, and I realize that I haven’t really thought about other possibilities. If you can think of some, please leave a comment below!