Comparative dynamics of exploited marine ecosystems

Anthropogenic stressors including excessive harvesting, climate change and eutrophication are recognized as dominant drivers of large marine ecosystem (LME) change. These changes include global declines in phytoplankton biomass, reductions in organism body sizes, and widespread fisheries stock collapses. The long-term goal of our research is to quantify the role of these and related stressors in determining the structure and function of LMEs and their differential vulnerability to perturbation. This knowledge is a critical requirement for forecasting when, where, and under what conditions ecosystem function degrades and/or productivity is altered to the point that traditional management strategies fail or resource yields collapse. It is also central to the successful development and implementation of ecosystem based management strategies designed to avoid recurring large scale ecological disasters such as the collapse of cod and other groundfish species in the northwest Atlantic in the early 1990s. Our research over the past decade has significantly enhanced this understanding of how LMEs are structured and function.

This proposal focuses on the next key elements in the development of this understanding. Four inter-related objectives will be pursued: 1) Evaluation of the multiple competing hypotheses advanced to explain patterns of trophic structure and function in LMEs. This project has two components: a) quantify and model the veracity of leading hypotheses advanced to explain spatial patterns in the type and strength of the macro-ecological relationships governing the dynamics of LMEs by drawing on published analyses of marine ecosystem function and b) use time series data from specific ecosystems to evaluate the temporal dynamics of trophic control in the global oceans. 2) Use 'downscaling' as a surrogate for controlled experimentation (impossible in LMEs) to decouple the relative importance of temperature and species diversity, identified as potential primary determinants of marine ecosystem structure. This will be achieved by exploiting the differential, bio-physical characteristics of the eastern and western Scotian Shelf ecosystems. 3) Quantitatively assess the impact on ecosystem structure, stability and productivity of recent global scale reductions in primary and secondary producer body sizes by incorporating into analyses of ecosystem function the rapidly expanding knowledge of the importance of evolved life history traits as determinants of population and ecosystem level properties. 4) Assess the efficacy of the "balanced fishing hypothesis" in the context of ecosystem based fisheries management. This research program is specifically designed to be tractable for the conduct of research at the Ph.D. and PDF levels while at the same time significantly advancing knowledge in an area of increasing worldwide importance.