Bull Kelp Adaptation

Project Overview

The Strait of Georgia, a body of water between Vancouver Island and the mainland of British Columbia, has experienced extensive bull kelp loss due primarily to warming oceans caused by climate change. Summer temperatures and annual rates of warming in the Strait are now typically higher than most bull kelp can tolerate, making restoration a particular challenge. Given the scale and acceleration of climate change,  a solution is urgently needed as these kelp provide critical habitat for migrating juvenile fish, including salmon. One promising solution is to identify kelp populations that have persisted through extreme warming events, such as marine heatwaves and seasonal fluctuations in weather patterns. These populations can potentially be seed sources for restoration, preserving and enhancing the natural genetic variation that grants them resilience.

Implementation

In 2023, the Kelp Rescue Initiative partnered with Hornby Island Diving, a local family-run dive center, to conduct an experiment testing for heat tolerance among bull kelp populations collected from various sites in the Strait of Georgia. As the epicenter of warming in the Strait, Hornby Island is an ideal location for such an experiment. Summer sea surface temperatures in the area often surpass 18°C, the point at which bull kelp starts to die. Decades ago, Hornby Island was surrounded by thick, extensive bull kelp beds, but these kelp forests have been absent now for over a decade, making it an important heritage 
site to restore.

Leveraging an existing array installed 10 years earlier for another kelp restoration project, the Kelp Rescue experiment hopes to answer key questions about bull kelp heat tolerance—answers that will be essential for successful restoration efforts. Bull kelp reproductive tissue was sourced from five populations along the Strait of Georgia, ranging from cooler to warmer, all of which persisted through a recent marine heatwave. Kelp spores from these five populations were seeded onto separate lines and deployed on the suspended array around 1 meter off the bottom of the sea floor. The lines were monitored through the spring and summer as the water warmed, and kelp growth and condition were recorded. This design, known to scientists as a “common garden experiment,” allows us to untangle how the different genetic compositions between populations influence growth and survival in a shared environment, in this case, a site with warmer waters.

Key Findings

This study confirmed that kelp from the five populations exhibited distinctly different growth patterns from each other at this warm water site. Kelp growing from soral material collected from a cooler nearby site had the best growth early in the season, and kelp sourced from the closest warm site had the greatest blade elongation rates. Kelp from some populations were able to grow reproductive tissue, yet all kelp showed signs of extreme tissue stress by July. Overall, this initial study demonstrated the value of selecting populations for restoration that have exhibited enhanced performance in warmer water.  But further work is needed; ocean temperatures were still too high later in the summer for bull kelp, even from the hardiest populations, to survive. This same study was repeated in 2024, and the Kelp Rescue team plans to explore similar questions with outplantings annually.