Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7507
Title: Stable isotopes and oceanographic modeling reveal spatial and trophic connectivity between terrestrial, estuarine and marine environments in Puget Sound, WA
Author: L. Conway-Cranos, Peter M. Kiffney, N. S. Banas, M. Plummer, Sean M. Naman, P. MacCready, John Bucci, M. H. Ruckelshaus
Publication Year: 2015
Journal: Marine Ecology Progress Series
Issue: 533
Pages: 15-28
Keywords: organic matter, energy flow, stream-estuary interactions, stable isotopes, oyster, land use,

Organic matter from autochthonous and allochthonous sources provides energy and nutrients to nearshore food webs including filter feeding bivalves.  In Puget Sound, WA where shellfish provide a variety of ecological, economic and cultural services, the degree to which shellfish rely on these different organic matter subsidies may be important for their management and the management of near–shore food webs in general.  We quantified terrestrial–marine connectivity in a large, temperate estuary using a combination of oceanographic modeling and isotopic mixing models.  We first examined spatial connectivity by modeling freshwater contributions of the major river basins to Puget Sound (potential connectivity), then estimated the relative contribution of terrestrial, near–shore and marine organic matter sources to near shore particulate organic matter (POM) (actual connectivity) and the diets of Pacific oysters (realized connectivity).

To estimate actual and realized connectivity, we analyzed the δ13C and 15N ratios of oyster tissue and primary producers from intertidal, offshore, salt marsh and upland habitats across the dry and wet seasons.  Using the Bayesian mixing model, MixSIR, oyster bed POM was found also to be composed largely of salt marsh plants and intertidal macrophytes.  Our results also indicate that much of the organic matter consumed by oysters originates from intertidal macrophytes (seaweeds and eelgrass) and salt marsh plants.  We tested the robustness of this assertion to two different trophic fractionation estimates, finding comparable proportionate contributions to shellfish diets of the organic matter sources we included in the model (upland vegetation, salt marsh plants, intertidal macrophytes, phytoplankton and benthic diatoms). 

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Theme: Ecosystem approach to improve management of marine resources
Foci: Characterize the interaction between marine, freshwater and terrestrial ecosystem components.