“Most research has focused on recent kelp forest losses resulting from well-known marine heatwaves, like the record-breaking ‘Blob’ heatwave that hit our coast a decade ago,” said Brian Timmer, a UVic Ph.D. student, National Geographic Explorer and lead author of the study, recently published in Ecological Applications.
These recent changes to our kelp forests have been intense. But our research shows that some areas of the BC coast have been warming much faster than the global average, and associated kelp declines began decades ago. We’ve been underestimating the magnitude of ocean-warming impacts for years,” said Chris Neufeld, co-author and senior aquatic ecologist at LGL Limited.
Researchers reconstructed historical baselines for bull kelp and associated macroalgae communities in the northern Salish Sea using maps, aerial photos, and scuba surveys from as far back as 1972. They then replicated identical surveys and photos in 2023 to directly compare kelp forest size and seaweed abundance over 50 years.
The historical records showed that there used to be massive bull kelp forests floating at the surface, covering more than 550 hectares of the northern Salish Sea near Comox and Denman Island. This increases the previous baseline of kelp forest size for this region by a factor of ten. None of those kelp forests remain today, and satellite records show that most of the bull kelp loss occurred between 1972 and 1984—well before the kelp losses documented during more recent marine heatwaves.
Timmer was also able to show that climate change was a driving factor in the loss of kelp forests. Using historical temperature data from Salish Sea lighthouses, he determined that by the time the kelp had disappeared in the late 1970s, the northern Salish Sea was substantially warmer than it was in the early 1900s. These temperatures have continued climbing to this day, meaning that the conditions have continually worsened since the initial kelp losses.
Underneath the water’s surface, Timmer found that the dominant, cold-adapted species of kelp and red algae had declined between 60 and 99 percent, particularly in shallow water. When these cold-adapted species died off, they were not replaced by warm-water species, which has likely resulted in habitat loss and reduced food availability for important coastal species like herring, rockfish and salmon.
We’ve been living with a completely warped sense of what ‘normal’ oceans look like. What we previously thought of as a baseline for the extent of our kelp forests was already post-collapse. Our research shows how important it is to have better baselines when investigating climate change impacts, so that we can make informed decisions about conservation, restoration and climate action, before further irreversible damage occurs,” said Brian Timmer, UVic Ph.D. student and lead author of the study.
Kelp forests are critical infrastructure for coastal ecosystems, providing habitat and food for fish, supporting fisheries, protecting shorelines and contributing to cultural and economic wellbeing.
This research was funded by Fisheries and Oceans Canada, the Natural Sciences and Engineering Research Council, the National Geographic Society and the Royal Canadian Geographic Society’s Trebek Initiative.
