The survival divide: cold vs. warm coastal zones
A recent study offers the longest record of kelp forest changes in Canadian waters, examining nearly 5,600 kilometers of the West Coast of Vancouver Island. The research found that kelp forests in colder, wave-exposed areas have survived well, with around 88 percent still present over the past century. In contrast, warmer, more sheltered regions show dramatic losses—over half of the kelp forests disappeared, likely due to rising sea surface temperatures in spring and summer.
Combining old charts with satellite data to track change
Scientists merged historical data from British Admiralty nautical charts, dating back to 1858, with satellite imagery collected from Sentinel-2 satellites between 2020 and 2023. The nautical charts marked kelp as landmarks because of their visibility to sailors. Modern satellite imaging uses the unique near-infrared reflectance of floating kelp canopies to map and monitor changes in these vital coastal ecosystems.
Climate refuges: kelp’s best chance in high-energy coasts
The research highlights how cooler and high-energy areas, where waves and cold water dominate, form a protective environment for kelp. These zones have preserved 97.5 percent of today's kelp canopy and boast the highest long-term persistence of forests, at 88 percent. The study suggests these regions act as climate refuges, shielding kelp from heat stress and marine heatwaves.
However, the situation in the warmest and most sheltered ecoregion is starkly different. Only 52 percent of the recorded kelp forests remain there, with the decline tied to elevated sea surface temperatures. These findings point to the importance of location and environmental conditions in shaping the fate of kelp forests.
The persistence measured here does not mean that kelp stayed in the same location continuously for 170 years. Instead, it indicates that kelp was found in the same places across both historical and modern records. These long-term snapshots help researchers understand trends over time, even if temporary disappearances occurred between surveys.
These discoveries offer vital insights for coastal conservation. Cooler, wave-affected coasts might hold the key to protecting biodiversity and supporting local fisheries. Researchers are calling on local and Indigenous leaders to use these results to shape climate resilience and marine protection strategies.
The study also underscores the value of long-term ecological data. Annual variations caused by storms or heatwaves can often mask broader trends.
The study highlights what scientists call “shifting baseline syndrome.” This term refers to the way each generation comes to see a degraded environment as normal because historical conditions are no longer remembered. Historical records, like the nautical charts used in the research, help paint a more accurate picture of coastal ecosystems before modern climate pressures took hold.
The findings also show that kelp decline is not uniform across the Pacific coast. While California and Washington have reported significant losses, British Columbia exhibits a more varied pattern. Some areas have seen decreases, others remain stable, and a few have even shown gains. The research suggests that local environmental conditions significantly influence kelp survival. Cooler, exposed areas seem more resilient, whereas warmer, sheltered regions face greater long-term risks.
The study, published in the journal Frontiers in Marine Science, brings together historical and modern data to show which kelp areas have remained stable for over a century. These findings could help prioritize conservation and restoration efforts for long-standing kelp refuges in Canada.