Title: Assessing nearshore pelagic trophic structure in the Puget

Title: Assessing nearshore pelagic trophic structure in the Puget Sound using community-level stable
isotope analysis
Presenter name: Sean Naman
Sean M. Naman1,2, Correigh M. Greene1, Casimir A. Rice1, Letitia Conway-Cranos1,
Jason E. Hall1, Joshua Chamberlin1
NOAA Fisheries, Northwest Fisheries Science Center, Seattle, WA
Department of Zoology, University of British Columbia, Vancouver BC
[email protected], 604-619-4274
Recent analysis of nearshore pelagic community structure in the greater Puget Sound has revealed
alarming trends including increasing blooms of gelatinous zooplankton (“jellyfish”) and the declines of
forage fish and salmon in some areas. Unfortunately, the mechanisms underlying these trends are unclear
due to a deficit of ecological understanding of this system. The analysis of food web structure, which
reflects the flow of carbon and nutrients, is useful to complement compositional (i.e. relative species
abundances) information to understand the energetic processes underlying pelagic communities and why
they may be changing. As a small part of a large, multi-trophic level assessment of Puget Sound’s pelagic
foodweb, we present a novel technique to examine food web structure using stable isotopes of carbon and
nitrogen. By calculating standard ellipse areas around isotope signatures of pelagic fish and jellyfish, we
are able to characterize how community-level trophic niches (which reflect both trophic length and basal
resource diversity) change across distinct oceanographic subbasins and seasonally. Preliminary results
indicate strong spatial and temporal structure in community niche widths with greater standard ellipse
areas in northern subbasins (Whidbey and Rosario basins) in spring months.
Session: Contributed
Student Presentation: Yes
Presentation type: Poster only