Abstract Title

Session S-02E: Kelp Trends

Proposed Abstract Title

An historical study of changes in floating kelp beds in Puget Sound and the Strait of Juan de Fuca

Keywords

Habitat

Location

Room 613-614

Start Date

30-4-2014 1:30 PM

End Date

30-4-2014 3:00 PM

Description

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.

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Apr 30th, 1:30 PM Apr 30th, 3:00 PM

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.