TY - JOUR
T1 - Linking predators to seasonality of upwelling
T2 - Using food web indicators and path analysis to infer trophic connections
AU - Thompson, Sarah Ann
AU - Sydeman, William J.
AU - Santora, Jarrod A.
AU - Black, Bryan A.
AU - Suryan, Robert M.
AU - Calambokidis, John
AU - Peterson, William T.
AU - Bograd, Steven J.
N1 - Funding Information:
This study was made possible by NSF Grant 0929017, NASA Grant NNX09AU3NG, and California OPC/California Sea Grant ENV-07. Field programs were supported by the USFWS and members and donors of PRBO (Farallon seabirds), NOAA-Fisheries (Stock Assessment Improvement Program, the Fisheries and the Environment Program, the US GLOBEC-Northeast Pacific Program (Peterson, Oregon copepods), the California Department of Fish and Game, and the Sonoma County Water Agency (SCWA). We thank PRBO Conservation Science for data contributions for this project. Analysis of remotely-sensed chlorophyll was facilitated by a grant from the Resources Law Group/Resources Legacy Fund Foundation. We thank Karina J. Nielsen for guidance on the use of path analysis and acknowledge Spencer Wood and the Sanak Island Food Web for feeding links.
PY - 2012/8
Y1 - 2012/8
N2 - Upwelling in eastern boundary current systems is a primary driver of ecosystem productivity. Typically, peak upwelling occurs during spring and summer, but winter upwelling may also be important to ecosystem functions. In this study, we investigated the hypothesis that winter and spring/summer upwelling, operating through indirect trophic interactions, are important to a suite of top predators in the California Current. To test this hypothesis, we collated information on upwelling, chlorophyll-a concentrations, zooplankton and forage fish, and related these to predator responses including rockfish growth, salmon abundance, seabird productivity and phenology (timing of egg-laying), and whale abundance. Seabird diets served in part as food web indicators. We modeled pathways of response using path analysis and tested for significance of the dominant paths with multiple regression. We found support for the hypothesis that relationships between upwelling and top predator variables were mediated primarily by intermediate trophic levels. Both winter and summer upwelling were important in path models, as were intermediate lower and mid trophic level functional groups represented by chlorophyll-a, zooplankton, and forage fish. Significant pathways of response explained from 50% to 80% of the variation of seabird (Cassin's auklet (Ptychoramphus aleuticus) and common murre (Uria aalge)), humpback whale (Megaptera novaeangliae) and Chinook salmon (Oncorhynchus tshawytscha) dependent variables, whereas splitnose rockfish (Sebastes diploproa) showed no significant response pathways. Upwelling and trophic responses for salmon were established for both the year of ocean entry and the year of return, with zooplankton important in the year of ocean entry and forage fish important in the year of return. This study provides one of the first comparative investigations between upwelling and predators, from fish to marine mammals and birds within a geographically restricted area, demonstrates often difficult to establish "bottom-up" trophic interactions, and establishes the importance of seasonality of upwelling to various trophic connections and predator demographic traits. Understanding change in the seasonality of upwelling is therefore required to assess dynamics of commercially and recreationally important upper trophic level species in eastern boundary current ecosystems.
AB - Upwelling in eastern boundary current systems is a primary driver of ecosystem productivity. Typically, peak upwelling occurs during spring and summer, but winter upwelling may also be important to ecosystem functions. In this study, we investigated the hypothesis that winter and spring/summer upwelling, operating through indirect trophic interactions, are important to a suite of top predators in the California Current. To test this hypothesis, we collated information on upwelling, chlorophyll-a concentrations, zooplankton and forage fish, and related these to predator responses including rockfish growth, salmon abundance, seabird productivity and phenology (timing of egg-laying), and whale abundance. Seabird diets served in part as food web indicators. We modeled pathways of response using path analysis and tested for significance of the dominant paths with multiple regression. We found support for the hypothesis that relationships between upwelling and top predator variables were mediated primarily by intermediate trophic levels. Both winter and summer upwelling were important in path models, as were intermediate lower and mid trophic level functional groups represented by chlorophyll-a, zooplankton, and forage fish. Significant pathways of response explained from 50% to 80% of the variation of seabird (Cassin's auklet (Ptychoramphus aleuticus) and common murre (Uria aalge)), humpback whale (Megaptera novaeangliae) and Chinook salmon (Oncorhynchus tshawytscha) dependent variables, whereas splitnose rockfish (Sebastes diploproa) showed no significant response pathways. Upwelling and trophic responses for salmon were established for both the year of ocean entry and the year of return, with zooplankton important in the year of ocean entry and forage fish important in the year of return. This study provides one of the first comparative investigations between upwelling and predators, from fish to marine mammals and birds within a geographically restricted area, demonstrates often difficult to establish "bottom-up" trophic interactions, and establishes the importance of seasonality of upwelling to various trophic connections and predator demographic traits. Understanding change in the seasonality of upwelling is therefore required to assess dynamics of commercially and recreationally important upper trophic level species in eastern boundary current ecosystems.
UR - http://www.scopus.com/inward/record.url?scp=84861454216&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84861454216&partnerID=8YFLogxK
U2 - 10.1016/j.pocean.2012.02.001
DO - 10.1016/j.pocean.2012.02.001
M3 - Article
AN - SCOPUS:84861454216
SN - 0079-6611
VL - 101
SP - 106
EP - 120
JO - Progress in Oceanography
JF - Progress in Oceanography
IS - 1
ER -