The Kelp It Is a Changin’

Kelp forests are a spectacular sight. These towering canopies of seaweed grow throughout the Central Coast of British Columbia and are home to a staggering variety of species. But these underwater forests don’t stay the same from year to year. For the past three years, Hakai Institute researchers have observed the size of kelp forests change before their eyes. To really understand this dynamic habitat, they observed the forest from all angles—both from beneath the waves and from a bird’s-eye view.

Under the Sea

Once you dive into a kelp forest you realize that it is bustling with biodiversity. Crabs, abalone, urchins, and sea cucumbers scavenge the seafloor for bits of kelp and debris that rain down from above. Rockfish, herring, and other fish dart between the kelp blades, which shelter them from predators.

Humans living on the coast also rely on the many ecosystem services that kelp forests provide from food to preventing coastal erosion. Yet while they’re critical, they aren’t static. These aquatic forests undergo profound changes—collapsing, recovering, and shifting—over timescales ranging from single seasons, to years, to decades.

In 2013, about 100 sea otters, part of the expanding population on the Central Coast, showed up next to the Hakai Field Station off Calvert Island. This was the first time they’d been there since they were nearly eradicated one hundred years prior.

Hakai researchers Erin Rechsteiner and Leah Honka observed that during 2013 and 2014, as expected, the otters ate sea urchins almost exclusively. These spiky herbivores comprised 85 percent of otters’ food in the first two years. This spelled big changes for the kelp beds because urchins and kelp have a very close relationship.

“Urchins are like underwater lawn mowers,” says Jenn Burt, a Hakai scholar and PhD candidate at Simon Fraser University who organizes Hakai’s kelp forest dive team.

Urchins love kelp, and they can eat a lot of it. But when sea otters are present, they effectively take the “lawn mowers” out of commission, and new kelps could colonize and grow. Now, three years of SCUBA surveys have provided Burt and her colleagues with a better understanding of how rocky reef communities, especially kelp, have changed since sea otters returned to the coast of Calvert Island. The dive team will return in July to document further changes.

Kelp Forests from the Air

Underwater surveys can show researchers the details, but a bird’s-eye view shows researchers how the overall size of kelp forests changes from year to year. To get this view, Keith Holmes and the Hakai geospatial team have compiled multiple years of high-resolution kelp forest images captured from satellites, planes, helicopters, and most recently, drones.

By comparing aerial images, the drastic changes in the kelp canopy coverage, pre- and post-sea otter arrival, become clear. Measurements from 2006 and 2012 show that the kelp forest patches near West Beach on Calvert Island were relatively small. Following the return of sea otters in 2013, the area of the kelp beds expanded by more than 200 percent.

While a major reason for this “kelp explosion” is fewer sea urchins in the area thanks to otters, kelp forest dynamics are complex. Kelp beds in 2015 were reduced by almost half compared to 2014, possibly due to other environmental factors such as storms or warmer water temperatures.

To get a complete view of this dynamic habitat means studying kelp from different perspectives. Whether looking up from the seafloor or down from the sky, researchers get to see the forest for the kelp.