From Ecology to Economics:
Incorporating Ecological Complexity to Understand
Effects of Multiple Stressors on a Coastal System

Most, if not all coastal systems are exposed to multiple stressors resulting from anthropogenic activities. Increased nutrient loadings, contaminants, harvesting, and general habitat degradation are each widespread and often occur in combination. An understanding of the cumulative and interactive effects of this array of stressors is thus important to our scientific understanding and sound management of coastal systems. In addition, the complexity of ecological systems, which arises from variation among species as well as trophic and spatial organization, can influence responses to both natural and anthropogenic stress. For the past 4 years COASTES (COmplexity And STressors in Estuarine Systems) has been using both manipulative experiments and modeling to examine the linkages between economics, land use, and ecology. COASTES focuses on the Patuxent River, a tributary of the Chesapeake Bay, as a model system. The goal of the multidisciplinary COASTES team is to improve the understanding of 1) the role of multiple stressors in coastal systems, and 2) the role that the complexity of natural systems plays in influencing their response to anthropogenic stress.

Many of the results of the COASTES program clearly indicate the importance of considering the complexity of natural systems both to predicting and understanding their responses to stress. In my seminar, I will give examples of these results from our watershed, fisheries, and multiple stressor work. Our watershed studies have found that the spatial arrangement of different land uses can be as important as the specific types of land use to the resulting nutrient loadings to streams. These results are a function of spatial variation in the underlying geology, including important differences between Piedmont and coastal plain areas. The implication of these results is that the appropriate management strategy will differ depending on the spatial scale of that management, and that the focus of local, watershed and regional agencies may need to be quite different. Fisheries and food web experiments and models indicate that interspecific differences in tolerances to low dissolved oxygen (a consequence of high nutrient loadings) can lead to sizeable shifts in the relative importance of different trophic pathways within the estuarine food web. Variation among species in behavioral responses to stressor exposure can alter encounter rates between predators and their prey, as well as the success of prey capture. In estuarine systems, this may increase the importance of gelatinous zooplankton relative to trophically similar fishes. Finally, mesocosm experiments that examined the interactive effects of nutrients and trace elements (both of which tend to be elevated in urbanized and agricultural areas), indicate the potential for trace elements to mask effects of increased nutrient loading. These experiments also indicate that the presence of multiple stressors may increase the temporal or spatial variability of a system independent of variation in anthropogenic loadings. In addition, altering the length of the food chain and the diversity of trophically similar species produce quite different effects on both the magnitude and variability of responses to stressors.