Taking Stock of Life in Transitioning Kelp Forests
As rocky reef monitoring enters its fifth year this week, we look back at highlights from last year’s survey.
We watch attentively from the boat as four divers plunge into the ocean off the rocky shore of Calvert Island. After they disappear under the surface, Jenn Burt, a Hakai scholar and PhD candidate at Simon Fraser University, inches the research vessel away from the rocks and surveys the scene as we bob in the gentle waves.
Save a pair of curious seals, we’re alone at the surface as far as the eye can see. Below us, though, life flourishes in transitioning kelp forests. The abundance of the diverse species that call this productive ecosystem home is what the scientific divers are seeking to determine today.
About 13 meters down, the researchers mark their survey area with three 30-meter measuring tapes (tied to rocks or kelp so they stay put), and count kelps, sea urchins, fish, and other mobile invertebrates, such as snails and crabs. They write down their observations—along with notes to each other—on a waterproof slate.
“Counting kelp underwater is like counting trees on land except you can’t talk, you can’t breathe like you normally do, and you can’t see sometimes,” jokes Burt, who is taking the day off diving to give me the tour. “Every time you go down, it’s an adventure.”
The purpose of these dive surveys—which have been taking place at 11 sites across the BC Central Coast every July since 2013—is to monitor the ecological changes on rocky reefs occurring as a result of changing ocean conditions and the recovery of sea otters.
The fur trade eliminated these important keystone predators from BC’s coastline in the 1800s, driving reefs to switch from kelp forests to urchin barrens. In the absence of sea otters, invertebrates become abundant and urchins gorge on kelp. But when sea otters return, which happened at this site three years ago, they fill their bellies with the spiky sea hedgehogs and the kelp begins to bounce back.
“Otters are like a forest fire,” says Burt. “They can come in like whoosh and clear out the key grazers that are limiting the kelp and then, as new rock space becomes available, an intense competition begins. The fast-growing, quickly colonizing kelp species are first to come back and then the slower, perennial species often take over. The different species are competing for light and space; when we’re counting kelps we’re finding out which ones are winning.”
Through her research, Burt and her colleagues are looking at the timeframe of sea urchin decline and kelp recovery in the region—and what drives the tipping points—while also documenting changes in fish and invertebrate communities. She explains that the kelp survey data can also be paired with Hakai oceanography data to understand the other important drivers in the system.
After an hour of intense counting, writing, and swimming in the deep forests below, the divers splash to the surface and clamber onto the boat, eager to swap stories of what they saw, including a sleeping octopus and a baby wolf eel.
Scientific diving on an urchin barren is slightly different to diving in a forest of stalked kelp. Video courtesy of Jenn Burt
After a lunch break, during which Burt collects some kelp to make lasagna (“Giant kelp blades are better than noodles for lasagna,” she insists), the team jumps in for a second dive, surveying at a shallower depth. While the divers are down, Burt discusses the wider social implications of her work, including First Nations traditional knowledge and governance within modern-day management.
Burt points out that before the fur trade, humans and otters coexisted. “We’re learning from traditional and local knowledge, along with archeological data, about how sea otters were used and managed in the past,” she says. “When the fur trade eliminated sea otters, it allowed urchin and shellfish abundance to boom to levels likely not observed historically, and that became everyone’s new baseline. Naturally, many people are angry when otters return because they reduce the availability of important local food sources. On the other hand, many people see the important role of otters in the system. It’s a complex situation.”
After analyzing her data, Burt hopes the results will contribute to ongoing community-based marine use planning and ecosystem-based management in the region. She also hopes her work will help provide coastal communities with information and tools for adapting to the return of sea otters and the ensuing ecosystem shifts.
Last summer marked the final season of Burt’s field research for her PhD, but the annual surveys have continued at Hakai as part of the new partnership with the Smithsonian’s Marine Global Earth Observatory, or MarineGEO. Hakai’s dive team is out on the water again this week investigating those same 11 sites. Each year, we build upon our knowledge of these underwater forests—and form new questions for the years to come.