End-to-end Energy Budgets in US-GLOBEC Regions

The proposed research addresses the overarching question: are marine food webs leading to fisheries controlled from the top-down, the bottom up, or a combination of the two? To address this question we will (1) compare end-to-end energy budgets of the 4 US-GLOBEC study regions in the context of top-down v. bottom-up forcing, (2) assess the skills of the regional models in capturing basic material fluxes, (3) extract diagnostics from the regional models that will be used to evaluate the effects of climate change and fishing pressure across GLOBEC regions and (4) develop quantitative methods to compare the diagnostics. Our inability to conduct controlled experiments is a major impediment to the scientific study of open sea ecosystems. An alternative is to compare studies of different ecosystems as a proxy for manipulations of the same system, particularly when climatic change and over-fishing provide inadvertent perturbations at the bottom and top of trophic webs. This approach is especially appropriate for end-to-end analysis of marine trophic webs with their complicated structure and complex dynamics. Such analyses depend on the comparability of the available data and the compatibility of the analytical methods. Ideally, such comparisons are based on identical methods for data collection and analysis. The four US GLOBEC programs provide one of the closest approximations to this ideal situation. All four systems have been subject to large amplitude trends or perturbations-- from climatic changes in the Antarctic Peninsula to over-fishing on Georges Bank. Extensive data sets are available for each region, covering most trophic components from nutrient input to top predators. Although there are some similarities among the four US-GLOBEC regions, there are striking differences in bottom depth and topography, circulation and stratification, annual cycles and trophic components, especially top predators. The major successes of GLOBEC have been in elucidating the processes underlying the dynamics of individual species in ecosystems characterized by diverse physical settings. The strictly “global” perspective has proved more elusive. At the same time there is an increasing demand for an ecosystem approach to management of marine resources subject to fishing pressures and climatic changes. Both of these challenges require an end-to-end approach that can provide the framework for detailed studies of particular species that are economically or environmentally significant. The US-GLOBEC sites provide sufficient diversity to test a range of methods as prologue to the larger global challenges. This modeling and synthesis project is a logical extension of studies initiated under the GLOBEC program that will advance the understanding of energy flow and trophic dynamics of marine food webs. Analyses of the response of marine ecosystems to climate change and their role in biogeochemical cycles have highlighted the importance of understanding trophic interactions. This point has been emphasized in the synthesis phase of GLOBEC and in the implementation phase of the Integrated Marine Biogeochemistry and Ecosystem Research (IMBER) program. Improving the understanding of trophic links in oceanic food webs is integral to the ability to understand and predict ecosystem responses to climate change and anthropogenic forcings.

These comparisons span a range of environments and food web structures and provide a basis for developing a framework that allows extension to systems not directly included in this analysis. By identifying and analyzing similarities and differences in marine food web structure and operation, this project provides a basis for development of future studies of marine food webs that have the goal of understanding end-to-end controls on trophic production. A strong aspect of the work is the integration of modeling and extensive biological data sets for regions to evaluate the biological processes, from primary producers to top predators, controlling energy flow, trophic transfers, carbon cycling, flux and export dynamics. The project is a unique opportunity for graduate students (2 included in the project) and postdoctoral investigators (2 included in the project) to become engaged in an interdisciplinary research project that uses quantitative and comparative analyses to understand marine food web structure and function in a range of ecosystems. The use of state-of-the-art modeling approaches that are coupled to data analyses provides opportunities to train students in a variety of disciplines (e.g. food web modeling, data analyses, data assimilation, marine ecology, fisheries management) that are needed to solve many of the important problems facing marine systems.