US-GLOBEC NEP Phase IIIa-CCS: Scale-dependent Dynamics of Top Trophic Predators and Prey: Toward Predicting Predator Response to Climate Change
C. Tynan [Woods Hole Oceanographic Institution], D. Ainley [H.T. Harvey & Assoc.]

Project Summary

We propose a collaborative synthesis to investigate the mesoscale and finer-scale spatial and temporal relationships between top predators (marine mammals, seabirds), their prey and physical-biological processes in the northern California Current System (CCS). We will use data sets collected during the multi-ship GLOBEC NEP effort that surveyed waters off Oregon and northern California in 2000 and 2002, including estimates of marine bird and mammal densities (continuous surveys) and coincident acoustic estimates of prey biomass using a multi-frequency array (backscatter subsequently validated by net sampling) and underway sampling of water-column structure and chlorophyll concentration using SeaSoar technology. Analyses of the 2000 data indicated that >40% of variation in the more abundant mammal and bird densities was explained by distance to upwelling-generated features (e.g., alongshore front, center of upwelling jet), acoustic backscatter at various frequencies (high frequencies explaining planktivore distribution; low frequencies explaining the piscivore distribution), and chlorophyll maximum.

Variability in the productivity of the CCS is notably large owing to climate variability on time scales ranging from days (upwelling) to interannual (ENSO) to decadal (Pacific Decadal Oscillation, PDO). For example, in response to the warm phase of the PDO 1976-1998, it is well known that zooplankton declined with a major reduction in its predators. In addition, major components of the food web have been removed by commercial fishing or whaling, with some species in a slow process of recovery (whales). While these trends can be best seen from a large-scale view, it is at the mesoscale or finer-scale perspective that predators are exploiting the patches of prey that become available. We will synthesize the above data to understand the scale-related dynamics between predators and prey in the CCS. Two major null hypotheses will be tested: 1) mesoscale forcing, that alters the alongshore upwelling front and equatorward jet, does not affect the cross-shelf and along-shelf density and community structure of top-predators; and 2) the spatial scale of plankton and nekton distribution, measured by spatial autocorrelation, is everywhere comparable to that of physical parameters; in turn, the spatial scale of planktivore or piscivore distributions is comparable to the scale of plankton and fish distributions, respectively.

We will construct a predictive model of factors affecting top-predator distribution based on 2000 data and will test it using 2002 data. We will also estimate predator abundance and distribution using general additive models (GAMs), from which we will construct a carbon flow model to estimate carbon egested, respired and sequestered by upper trophic levels (as well as carbon removed by migrants). It may be greater than the amount of carbon advected offshore by meandering jets. We will use several modeling approaches to determine the magnitude and significance of prey correspondence or depletion at a range of scales. We will examine spatial heterogeneity at two levels of the ecosystem: the density or patch size of prey relative to physical oceanographic features; and the density of predators relative to their prey.

Intellectual Merit - The ecological roles of top predators in structuring communities and affecting the flow of carbon in shelf systems are known to be significant. What is less well understood is how the spatial and temporal variability in mesoscale forcing influences cross-shelf and along-shelf structure of mid-trophic communities and the transfer of carbon from zooplankton and fish to top predators. Therefore, in order to understand how climate variability affects populations of top-trophic species through changes in marine production and prey availability, a study such as ours is necessary to examine how predators interact with biophysical structure of their habitat at the spatio-temporal scales in which they forage on a daily basis.

Broader Impacts - The syntheses proposed herein provide a valuable baseline, for the early part of this century, on top predator response to several scales and sources of variability in the northern CCS. In addition, the synthesis forwards the longer-term development of predictive biophysical models of occurrence patterns of top-predators (many of which are endangered species) in the CCS. Evolution of such models will assist with resource management and planning of human activities (e.g., major fisheries, 5 marine sanctuaries, transportation and commerce) in the northern California Current ecosystem off the west coast of the U.S.

NSF Award Summary

The ecological roles of top predators in structuring communities and affecting the flow of carbon in shelf systems are known to be significant. What is less well understood is how the spatial and temporal variability in mesoscale forcing influences cross-shelf and along-shelf structure of mid-trophic communities and the transfer of carbon from zooplankton and fish to top predators. The investigators will examine mesoscale and finer-scale spatial and temporal relationships between top predators (marine mammals, seabirds), their prey and physical-biological processes in the northern California Current System (CCS) with data sets collected during the multi-ship GLOBEC NEP effort that surveyed waters off Oregon and northern California in 2000 and 2002. Variability in the productivity of the CCS is notably large owing to climate variability on time scales ranging from days (upwelling) to interannual (ENSO) to decadal (Pacific Decadal Oscillation, PDO). While these trends can be best seen from a large-scale view, it is at the mesoscale or finer-scale perspective that predators are exploiting the patches of prey that become available. Two major null hypotheses will be tested: 1) mesoscale forcing, that alters the alongshore upwelling front and equatorward jet, does not affect the cross-shelf and along-shelf density and community structure of top predators; and 2) the spatial scale of plankton and nekton distribution, measured by spatial autocorrelation, is everywhere comparable to that of physical parameters; in turn, the spatial scale of planktivore or piscivore distributions is comparable to the scale of plankton and fish distributions, respectively. The investigators will construct a predictive model of factors affecting top-predator distribution based on 2000 data and will test it using 2002 data. They will also estimate predator abundance and distribution using general additive models and construct a carbon flow model to estimate carbon egested, respired and sequestered by upper trophic levels (as well as carbon removed by migrants). Several modeling approaches will be used to determine the magnitude and significance of prey correspondence or depletion at a range of scales. Spatial heterogeneity will be examined at two levels of the ecosystem: the density or patch size of prey relative to physical oceanographic features and the density of predators relative to their prey. The syntheses proposed herein provide a valuable baseline, for the early part of this century, on top predator response to several scales and sources of variability in the northern CCS. In addition, the synthesis forwards the longer-term development of predictive biophysical models of occurrence patterns of top-predators (many of which are endangered species) in the CCS. Evolution of such models will assist with resource management and planning of human activities (e.g., major fisheries, 5 marine sanctuaries, transportation and commerce) in the northern California Current ecosystem off the west coast of the U.S.

This page was last updated on March 14, 2007.

Maintained by:
Hal Batchelder
College of Oceanic and Atmospheric Sciences
Oregon State University
Corvallis, OR 97331-5503
phone: 541-737-4500; FAX 541-737-2064