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April 16, 2025

Kelp forests are often called the rainforests of the sea—vital coastal ecosystems that provide habitat, buffer shorelines, and support marine biodiversity. In Haida Gwaii, a remote archipelago off the northwest coast of British Columbia, these underwater forests have long played an essential role in both ecological and cultural life. But how have these systems changed over time?

A new study led by UVic Geography researchers and the SPECTRAL Remote Sensing laboratory offers one of the most comprehensive looks to date at the long-term history of kelp forests in the region. Drawing on a unique blend of archival maps, satellite imagery, and insights from Indigenous knowledge, the study traces patterns of kelp abundance and loss across Haida Gwaii from 1867 to 2021.

Published in the journal Frontiers in Marine Science, the research challenges conventional narratives about kelp decline, offering new evidence that regional climate drivers—such as marine heatwaves, the Pacific Decadal Oscillation (PDO), and El Niño–Southern Oscillation (ENSO)—have played a far more significant role than previously understood.

A Historical Baseline Reconstructed

To investigate long-term change, the research team compiled historical data from a wide range of sources, including archival Bristish nautical charts from the 19th and early 20th centuries, and compared them with modern satellite imagery and in-situ field surveys. In doing so, they created a spatially explicit, multi-century dataset that allows for unprecedented analysis of kelp forest dynamics over time. 

This approach uncovered a surprising result: since the 1970s, consistently stable kelp began showing significant declines, with a regional loss of approximately 5% per decade. 

Climate Drivers, Not Just Grazing

While urchin grazing - the primarily culprit for kelp loss in many regions around the world - is still a factor in many areas, the study highlights that long-term kelp loss in Haida Gwaii correlates more strongly with large-scale climate patterns and marine heatwaves. The researchers found that kelp coverage decreased during warm phases of ENSO and the PDO, and during recent periods of extreme ocean warming.

The study examined kelp changes across three scales: regional (800 km²), subregional, and local (1 km coastal segments). One of the most striking insights was how much the impacts of climate change varied across even small distances.

In some areas, kelp forests declined rapidly and didn’t recover. In others—just a few kilometers away—kelp remained stable or rebounded after disturbance. This suggests that environmental heterogeneity (differences in things like wave action, wind exposure, and sea surface temperature) plays a major role in shaping ecosystem resilience. It also challenges the idea that climate impacts are uniform across a region. Instead, microclimates and local environmental contexts make all the difference. These insights can help conservation efforts by showing where kelp is most vulnerable and where it might still thrive.

To effectively protect ecosystems in a warming world, place-based science and local data are essential.

Collaboration and Indigenous Knowledge

A critical dimension of the study was the integration of local and Indigenous knowledge. The researchers worked with partners from the Council of the Haida Nation and drew on community-based observations to help ground data and guide areas of focus.

This collaboration adds a deeper understanding of the relationship between coastal communities and kelp ecosystems—highlighting not only the ecological importance of kelp, but its role in food systems, cultural practices, and long-standing stewardship traditions.

Informing Future Conservation

The study's findings carry important implications for marine protection and climate adaptation efforts, emphasizing that restoring kelp habitats will require strategies that go beyond managing herbivore populations. Instead, there’s a need to account for long-term climate trends and prioritize resilience in the face of warming waters.

This research is part of a larger commitment by UVic Geography to support community-led conservation and advance understanding of coastal change. By combining modern technology, historical analysis, and Indigenous collaboration, UVic researchers are helping to build a more complete picture of ecosystem transformation in a rapidly changing world.

Read the full study here: