Kelp bed community shifts following sea star wasting syndrome in Howe Sound, British Columbia
Presentation Abstract
Echinoderm population cycles may be important drivers of ecological shifts on kelp bed communities. In Howe Sound, British Columbia, kelp beds are dominated the perennial Agarum fimbriatum, which provides important habitat for a variety of fish and invertebrates. The northeast Pacific recently experienced a mass mortality of sea stars beginning in early September 2013, and the sunflower star Pycnopodia helianthoides – a previously abundant predator of bottom-dwelling invertebrates –disappeared from many sites in a matter of weeks. By comparing the abundance of invertebrates and kelp before and after the sea star mortality event, we observed a four-fold increase in the abundance of green sea urchins and a 50% decline in kelp cover. Surveys were conducted during summer when Agarum blade size and growth is greatest. Here, we present the hypothesis that some of the changes we observed resulted from a trophic cascade involving sea stars, urchins and kelp. Behavioural experiments conducted in situ suggest predation release as a key mechanism underpinning the shift in urchin numbers. To quantify the impact of higher urchin abundance on kelp, we conducted 10 independent grazing experiments where A. fimbriatum was transplanted to barren rocky reefs of various green urchin densities. At high densities, kelp declined more that 40% in as little as 24 hrs. A. fimbriatum also provides key settlement habitat for the spot prawn Pandalus platyceros, so we predict the trophic cascade may impact spot prawn abundance in future years.
Keywords: algae, trophic cascade, echinoderm, sea star wasting, mass mortality event
Session Title
Kelp and Eelgrass
Conference Track
Habitat
Conference Name
Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)
Document Type
Event
Start Date
2016 12:00 AM
End Date
2016 12:00 AM
Location
2016SSEC
Type of Presentation
Oral
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--British Columbia--Howe Sound; Echinodermata--Population variability analysis--British Columbia--Howe Sound; Starfishes--Diseases--British Columbia--Howe Sound
Geographic Coverage
Salish Sea (B.C. and Wash.); Howe Sound (B.C.)
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
Kelp bed community shifts following sea star wasting syndrome in Howe Sound, British Columbia
2016SSEC
Echinoderm population cycles may be important drivers of ecological shifts on kelp bed communities. In Howe Sound, British Columbia, kelp beds are dominated the perennial Agarum fimbriatum, which provides important habitat for a variety of fish and invertebrates. The northeast Pacific recently experienced a mass mortality of sea stars beginning in early September 2013, and the sunflower star Pycnopodia helianthoides – a previously abundant predator of bottom-dwelling invertebrates –disappeared from many sites in a matter of weeks. By comparing the abundance of invertebrates and kelp before and after the sea star mortality event, we observed a four-fold increase in the abundance of green sea urchins and a 50% decline in kelp cover. Surveys were conducted during summer when Agarum blade size and growth is greatest. Here, we present the hypothesis that some of the changes we observed resulted from a trophic cascade involving sea stars, urchins and kelp. Behavioural experiments conducted in situ suggest predation release as a key mechanism underpinning the shift in urchin numbers. To quantify the impact of higher urchin abundance on kelp, we conducted 10 independent grazing experiments where A. fimbriatum was transplanted to barren rocky reefs of various green urchin densities. At high densities, kelp declined more that 40% in as little as 24 hrs. A. fimbriatum also provides key settlement habitat for the spot prawn Pandalus platyceros, so we predict the trophic cascade may impact spot prawn abundance in future years.
Keywords: algae, trophic cascade, echinoderm, sea star wasting, mass mortality event
