Kelp forests once covered part of the northern Salish Sea, UVic study finds

Near the breakwater along Dallas Road in Victoria, the water is teeming with rich kelp forests just beneath the surface.

“They’re doing quite well because the water stays quite cold,” said Brian Timmer, a PhD student at the University of Victoria (UVic). “But as you go sort of further abroad into different parts of B.C., you get into these little pockets of warming that we call microclimates.”

Those areas were once thick with kelp forests too, but they’ve long since disappeared, according to a new study Timmer led out of UVic, published in Ecological Applications.

His research team compiled historical data for kelp and its associated macroalgae communities in the northern Salish Sea by using maps, scuba surveys and aerial photos dating back to 1972.

In 2023, they replicated those images and surveys to draw direct comparisons.

The study found that sweeping bull kelp forests used to cover more than 5.5-million square metres of the northern Salish Sea’s surface, around the Comox and Denman Island region.

That is 10 times what experts agreed on as the previous baseline, which Timmer said was established around the year 2000. 

None of those kelp forests remain today — satellite imagery in the area shows the majority of the bull kelp loss occurred in 12 years, between 1972 and 1984.

Recent heatwaves — like the “Blob” heatwave from 2014 to 2016 — were thought to be causing B.C.’s bull kelp forests to disappear, according to this study, but Timmer’s research shows the most substantial loss may have occurred decades before.

Timmer said the study focused on a pocket of warm water within the Strait of Georgia, near Comox and Denman Island, that falls within the top 10 per cent of global ocean warming temperatures.

Over the past 50 years, sea surface temperatures at the Chrome Island lighthouse, off Denman Island’s southern tip, have warmed by 0.25 C per decade, for a 1.66 C increase in total, the study found.

It’s these periods of accelerated warming that experts say damage kelp populations the most.

Experts refer to kelp as a foundation species and a primary producer. Kelp is vital to supporting life in marine ecosystems, providing an abundance of food and habitats for many sea animals.

The UVic study found that before major losses to bull kelp forests between 1972 and 1984, that area of the Salish Sea was covered by 10 times as much kelp as was previously thought to be the baseline, which was established more than 20 years ago.

“It shows a classic shifting baseline problem,” said William Cheung, a professor at the University of British Columbia (UBC) and Canada Research Chair in Ocean Sustainability and Global Change.

Cheung explained that we often compare historical changes to the baselines we establish at our generation, which can be very different from the baselines past generations saw.

“It’s really important to fill those gaps so we have a proper baseline and understanding of the trends, to inform our current actions for conservation and for climate adaptations.”

Researchers at UVic found that sugar kelp in the region declined by 78 per cent, and red bladed algae by 98.5 per cent since 1972. Timmer thinks it is the warming of waters along B.C.’s coast that’s driving the decline of healthy kelp and microalgae communities.

Cheung said he believes if the study were repeated elsewhere in B.C., there would likely be more areas that were once home to an abundance of kelp, and aren’t any longer.

In an effort to curb that trend, Timmer works with the Kelp Rescue Initiative and First Nations to help restore kelp forests in the province.

“One thing that we are looking at is making sure to try to protect these areas as much as possible.”

He said it isn’t a simple solution, but identifying areas that are suitable as long-term habitats for kelp and replanting kelp species is where to start.