Top Down Control of Canopy-Forming Kelp by Crustacean Consumers
Presentation Abstract
Bull kelp (Nereocystis luetkeana) plays an important ecological role in nearshore subtidal ecosystems around the Salish Sea, including primary production, supply of detrital material, and creation of three-dimensional habitat for other species. Large crustacean consumers such as the northern kelp crab (Pugettia producta) may influence kelp distribution and abundance. Exclusion cages at a subtidal field site near Point Caution on San Juan Island were used to assess herbivory on juvenile N. luetkeana. The four treatments using mesh and concrete blocks with attached juvenile bull kelp, were: unenclosed, partially mesh enclosed, fully mesh enclosed, and fully mesh enclosed with P. producta inside. The only treatment in which juvenile bull kelp increased in mass or blade length was the fully caged treatment. To assess crabs’ potential to exert top-down control on kelp bed species, we quantified feeding electivities and preferences of kelp crabs (P. producta) in laboratory feeding trials on a range of prey items, including several macroalgal species and snails. In these trials, kelp crabs were starved for 12 hours and then allowed to feed for 12 hours. In all trials, kelp crabs elected to eat more N. luetkeana than any other macroalga tested; in the kelp vs. snail trial, they showed no significant preference. In a follow-up laboratory feeding trial, kelp crabs were starved for 12 hours, then allowed to feed for 12 hours on two similar-sized pieces of N. luetkeana. One of the pieces was freshly collected and the other aged in a dark, flowing seawater tank for one week. On average, P. producta consumed 6.0 g of fresh blade and 1.5 g of aged blade. The results of these experiments indicate that kelp crabs frequently elect to eat fresh N. luetkeana over other macroalgae, in addition to their role as detritivores, and may exert top-down control on bull kelp distribution and abundance when kelp sporophytes are small and therefore most vulnerable to catastrophic herbivory.
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)
Nereocystis luetkeana--Salish Sea (B.C. and Wash.); Kelp bed ecology--Salish Sea (B.C. and Wash.); Crabs--Food--Salish Sea (B.C. and Wash.); Predation (Biology)--Salish Sea (B.C. and Wash.)
Geographic Coverage
Salish Sea (B.C. and Wash.)
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
Top Down Control of Canopy-Forming Kelp by Crustacean Consumers
Room 613-614
Bull kelp (Nereocystis luetkeana) plays an important ecological role in nearshore subtidal ecosystems around the Salish Sea, including primary production, supply of detrital material, and creation of three-dimensional habitat for other species. Large crustacean consumers such as the northern kelp crab (Pugettia producta) may influence kelp distribution and abundance. Exclusion cages at a subtidal field site near Point Caution on San Juan Island were used to assess herbivory on juvenile N. luetkeana. The four treatments using mesh and concrete blocks with attached juvenile bull kelp, were: unenclosed, partially mesh enclosed, fully mesh enclosed, and fully mesh enclosed with P. producta inside. The only treatment in which juvenile bull kelp increased in mass or blade length was the fully caged treatment. To assess crabs’ potential to exert top-down control on kelp bed species, we quantified feeding electivities and preferences of kelp crabs (P. producta) in laboratory feeding trials on a range of prey items, including several macroalgal species and snails. In these trials, kelp crabs were starved for 12 hours and then allowed to feed for 12 hours. In all trials, kelp crabs elected to eat more N. luetkeana than any other macroalga tested; in the kelp vs. snail trial, they showed no significant preference. In a follow-up laboratory feeding trial, kelp crabs were starved for 12 hours, then allowed to feed for 12 hours on two similar-sized pieces of N. luetkeana. One of the pieces was freshly collected and the other aged in a dark, flowing seawater tank for one week. On average, P. producta consumed 6.0 g of fresh blade and 1.5 g of aged blade. The results of these experiments indicate that kelp crabs frequently elect to eat fresh N. luetkeana over other macroalgae, in addition to their role as detritivores, and may exert top-down control on bull kelp distribution and abundance when kelp sporophytes are small and therefore most vulnerable to catastrophic herbivory.
