Mapping Seattle's Historical Kelp Forests
Analysis of aerial imagery from 1984 provides a snapshot of kelp forest resilience and loss in Seattle over the last four decades.
This StoryMap is the visual companion to a Report by the Nearshore Habitat Program at Washington State Department of Natural Resources. For an in-depth look at this project, access the report here .
Slides from 1984 show an aerial view of a kelp forest wrapping from Smith Cove to the 32nd Ave beach,
A Box of Old Slides
Box of 35mm slides captured by Ron Thom in 1984.
This project centers on a box of 35mm slides of aerial photographs captured on September 7th, 1984.
The three dozen slides were originally captured by Ron Thom (University of Washington) as part of a baseline study for the location of a King County wastewater treatment outfall.
The images were likely captured around low tide, which was about 0 m MLLW at 9:52am that day. Shadow angles and the presence of floating kelp on the surface support a morning low tide timing.
These are color infrared photographs, but many of the red hues of the images have faded over time.
Image Analysis
Change in Kelp Forests
In summary, kelp losses were detected at all of the areas surveyed between 1984 and 2019.
So What Happened?
The drivers of floating kelp decline in Central Puget Sound remain uncertain, but many factors including temperature, nutrient availability, and shoreline development may play a role. While we did not examine environmental parameters in this study, we know that the Seattle shorelines surveyed in this project have been highly modified over the last 150+ years. At both Magnolia and Lincoln Park, major shoreline modifications have occurred between the survey dates.
Conclusion
Subsurface blades of bull kelp visible along the Seattle waterfront. Photo by Gray McKenna, July 2022.
Kelp forests are highly dynamic systems, and the history of kelp along this shoreline is far longer and more complex than what these two snapshots in time can tell us.
Every dataset, current and historical, brings us closer to understanding these critical ecosystems and how they have changed over time. This analysis provided another piece of the puzzle of the historic distribution of floating kelp along Seattle shorelines and found previously undocumented losses.
Understanding how floating kelp has changed over time is essential to identify and reverse declines in kelp forests in Washington. As a more complete picture of kelp spatiotemporal distribution in Central Puget Sound emerges, further research into potential stressors like shoreline development may help identify priority areas for conservation and restoration and inform effective stewardship and management of these critical habitats.
Acknowledgements
The Nearshore Habitat Program is part of the Aquatic Resources Division within the Washington State Department of Natural Resource, the steward for state-owned aquatic lands. The Nearshore Habitat Program monitors and evaluates the status and trends of marine vegetation for DNR, in association with the Puget Sound Partnership as a component of the Puget Sound Ecosystem Monitoring Program.
The Nearshore Habitat Program is grateful to the WA State Legislature for providing funding for DNR to map current and historical floating kelp distributions throughout the state using archival imagery to fill critical knowledge gaps.
The primary author of this StoryMap is Gray McKenna. Helen Berry, Danielle Claar, and Tyler Cowdrey provided technical and subject matter expertise critical to the development of this project. Tim McClure, Bart Christiaen, Pete Dowty, Hayler Turner, Lauren Johnson, and Emily Smith generously provided expert review of the photographs. This report focuses on a dataset originally collected by Ron Thom (University of Washington). We are grateful to him for sharing his many years of research and knowledge.
Contact: nearshore@dnr.wa.gov.
Learn More
Learn more about kelp mapping and monitoring at WA DNR:
