An historical study of changes in floating kelp beds in Puget Sound and the Strait of Juan de Fuca
Presentation Abstract
This study assessed changes in floating kelp canopy area through comparing historical data to recent surveys. It updated a 1990 synthesis by Thom and Hallum that found the length of shoreline with kelp forests increased substantially between 1912 and 1978, with the largest relative increases in South and Central Puget Sound. We extended the temporal comparison to 2013 using boat-based canopy mapping, airphoto-based surveys, and existing studies by other scientists. We observed extensive losses in the length of shoreline with floating kelp between 1978 and 2013 in the areas we surveyed in South Puget Sound and around Bainbridge Island, with the exception of a limited number of beds which persisted throughout the time period. In Elliott Bay, bull kelp occurred along an equal or greater length of shoreline compared to historical data sets. More detailed, inter-annual comparisons were possible along the Strait of Juan de Fuca using DNR’s long-term monitoring results from 1989 to 2012. These data show large inter-annual variability in kelp canopy extent and very few losses of the type observed in South and Central Puget Sound. Overall, despite uncertainty associated with diverse data sets, our updated temporal comparison suggests strongly that floating kelp has decreased in South and Central Puget Sound in recent decades. This finding is supported by small area surveys and observations. The causes of the observed changes are not understood. Some candidates include competition with native or non-native vegetation, water quality degradation, substrate alteration, changes in grazer populations, and physical disturbance.
Session Title
Session S-02E: Kelp Trends
Conference Track
Habitat
Conference Name
Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)
Document Type
Event
Start Date
30-4-2014 1:30 PM
End Date
30-4-2014 3:00 PM
Location
Room 613-614
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Kelp bed ecology--Washington (State)--Puget Sound; Kelp bed ecology--Juan de Fuca, Strait of (B.C. and Wash.)
Geographic Coverage
Puget Sound (Wash.)--Environmental conditions; Juan de Fuca, Strait of (B.C. and Wash.)--Environmental conditions; Salish Sea (B.C. and Wash.)--Environmental conditions
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
An historical study of changes in floating kelp beds in Puget Sound and the Strait of Juan de Fuca
Room 613-614
This study assessed changes in floating kelp canopy area through comparing historical data to recent surveys. It updated a 1990 synthesis by Thom and Hallum that found the length of shoreline with kelp forests increased substantially between 1912 and 1978, with the largest relative increases in South and Central Puget Sound. We extended the temporal comparison to 2013 using boat-based canopy mapping, airphoto-based surveys, and existing studies by other scientists. We observed extensive losses in the length of shoreline with floating kelp between 1978 and 2013 in the areas we surveyed in South Puget Sound and around Bainbridge Island, with the exception of a limited number of beds which persisted throughout the time period. In Elliott Bay, bull kelp occurred along an equal or greater length of shoreline compared to historical data sets. More detailed, inter-annual comparisons were possible along the Strait of Juan de Fuca using DNR’s long-term monitoring results from 1989 to 2012. These data show large inter-annual variability in kelp canopy extent and very few losses of the type observed in South and Central Puget Sound. Overall, despite uncertainty associated with diverse data sets, our updated temporal comparison suggests strongly that floating kelp has decreased in South and Central Puget Sound in recent decades. This finding is supported by small area surveys and observations. The causes of the observed changes are not understood. Some candidates include competition with native or non-native vegetation, water quality degradation, substrate alteration, changes in grazer populations, and physical disturbance.
