Top-down control of subtidal communities
What do rockfish eat?
Copper rockfish are the most abundant demersal predator in the San Juan Islands. Their diet has been studied in the past, but recent and local diet data is missing. Because the local populations of three species of rockfish have recently been declared threatened or endangered under the ESA, and other species of rockfish are categorized as vulnerable by WDFW, conducting this research without killing the subjects is critical. Gastric lavage (“stomach pumping”) has been used with many other species of fishes. We successfully adapted the method for use with rockfish.
How many predators are where?
One of the first steps to determining the impact of predators on other community members is to determine how many predators there are, and how their abundance differs in space. I conducted fish surveys at twelve sites in San Juan Channel several times each year for three years. We used a modified version of surveys that have been conducted in San Juan Channel since the 1970s
How do predators influence prey?
I used the fish surveys to choose two locations with high predator abundance. At each of the two locations I prepped five sites with anchors made of rebar and z-spar to which I attached 2×2 m cages made of pvc and polypropylene mesh. These cages excluded predatory fishes but allowed access to smaller prey species like shrimp, crabs and sculpins.
I also combined the surveys of predator abundance with surveys of prey abundance. At the same twelve sites in San Juan Channel I established permanent transects at five depths, where I counted and measured shrimp, crabs and sculpins every fall for four years.
Further community impacts?
In addition to quantifying the organisms that were likely prey items for predatory fishes, I wanted to determine if predator influence cascades beyond one trophic link. Along the same transects I used for quantifying shrimp, crabs and sculpins (5 depths at twelve sites, every fall for four years), I quantified other mobile invertebrates (e.g. stars, urchins, cucumbers, nudibranchs…) and took photographs of ten random 0.1 m2 quadrats to monitor sessile invertebrate and algal abundance. I am looking for patterns in distributions that correlate with predator abundance.
I also monitor the same kinds of patterns in the predator exclusion cages, counting and measuring mobile fauna and photographing sessile organisms.
Shaw Island Research Grant (2013-2014), PI: Kevin Turner
NSF Biological Oceanography Grant #OCE 0850809 (2009-2013), PI: Kenneth Sebens
NSF GK-12 Grant #DGE 0742559 (2008-2010), PIs: Kenneth Sebens, Daniel Grunbaum, David Armstrong
(* indicates undergraduate student co-author)
TURNER, K., *W. Rung and K. Sebens. Accepted. Non-lethal diet analysis of copper rockfish in the San Juan Archipelago. Northwest Science.
Elahi, R., C. Birkeland, K. Sebens, K. TURNER and T. Dwyer. 2013. Limited change in the diversity and structure of subtidal communities over four decades. Marine Biology. http://link.springer.com/article/10.1007%2Fs00227-013-2308-3
TURNER, K. and K. Sebens. 2011. Impacts of lingcod and rockfish on benthic community structure in the San Juan Islands, Washington. In Tonnes, D. (editor). 2012. Rockfish recovery in the Salish Sea; Research and management priorities, Workshop held June 28th and 29th, 2011. National Marine Fisheries Service, Protected Resources Division. Download PDF
TURNER, K. 2008. Indirect effects of marine preserves in the San Juan Islands. Electronic Journal of Applied Multivariate Statistics 1:19-29. Download PDF
(* indicates undergraduate student co-author)
Salish Sea Ecosystem Conference, “Facilitation of rockfish by octopus in the Salish Sea,” April 2014 (Seattle, WA)
Benthic Ecology Meeting, “Top-down control of prey populations by predatory fishes in the San Juan Islands, WA,” March 2013 (Savannah, GA)
Society for Integrative and Comparative Biology, “Predatory fish impacts on benthic community structure,” January 2012 (Charleston, SC).
Salish Sea Ecosystem Conference, “Impacts of rockfish and lingcod on benthic community structure,” October 2011 (Vancouver, BC).
Workshop on Rockfish Recovery in the Salish Sea, “Impacts of rockfish and lingcod on benthic community structure in the San Juan Islands,” June 2011 (Seattle, WA).
Society for Integrative and Comparative Biology, “Predator impacts on benthic community structure in the San Juan Islands,” January 2011 (Salt Lake City, UT).
American Association for Underwater Sciences, “Predator exclusion experiments in the San Juan Islands,” March 2010 (Honolulu HI).
Society for Integrative and Comparative Biology, “Predator effects on benthic communities in the San Juan Islands,” January 2010 (Seattle, WA).
Western Society of Naturalists, “Predator effects on benthic communities in the San Juan Islands,” November 2009 (Seaside, CA).
International Temperate Reef Symposium, “Indirect effects of marine protected areas on early community development in the San Juan Islands,” January 2009 (Adelaide, Australia).
Western Society of Naturalists, “Facilitation of rockfish by octopuses in the Salish Sea,” November 2013 (Oxnard, CA).
Western Society of Naturalists, “Predatory fish impacts on benthic community structure,” November 2011 (Vancouver, WA).
Western Society of Naturalists, “Benthic community structure in the San Juan Islands,” November 2010 (San Diego, CA).
American Society of Limnology and Oceanography, “Predator effects on benthic communities in the San Juan Islands,” February 2010 (Portland, OR).
American Museum of Natural History, Center for Biodiversity and Conservation Spring Symposium, “Indirect effects of marine reserves on several species of snails, small crabs and scallops in San Juan Channel, Washington,” March 2004 (New York, NY).