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Gerald Niemi,¹ Denice Wardrop,² Robert Brooks,² Susan Anderson,³ Valerie Brady,¹ Hans Paerl,⁴ Chet Rakocinski,⁵ Marius Brouwer,⁵ Barbara Levinson,⁶ and Michael McDonald⁷

¹Natural Resources Research Institute, University of Minnesota, Duluth, Minnesota, USA; ²Cooperative Wetlands Center, Pennsylvania State University, University Park, Pennsylvania, USA; ³Bodega Marine Laboratory, University of California Davis, Bodega Bay, California, USA; ⁴Institute of Marine Sciences, University of North Carolina-Chapel Hill, Morehead City, North Carolina, USA; ⁵Department of Coastal Sciences, University of Southern Mississippi, Ocean Springs, Mississippi, USA; ⁶U.S. Environmental Protection Agency, National Center for Environmental Research, Washington DC, USA; ⁷U.S. Environmental Protection Agency, Environmental Monitoring and Assessment Program, Research Triangle Park, North Carolina, USA

Abstract
More than half the world's human population lives within 100 km of the coast, and that number is expected to increase by 25% over the next two decades. Consequently, coastal ecosystems are at serious risk. Larger coastal populations and increasing development have led to increased loading of toxic substances, nutrients and pathogens with subsequent algal blooms, hypoxia, beach closures, and damage to coastal fisheries. Recent climate change has led to the rise in sea level with loss of coastal wetlands and saltwater intrusion into coastal aquifers. Coastal resources have traditionally been monitored on a stressor-by-stressor basis such as for nutrient loading or dissolved oxygen. To fully measure the complexities of coastal systems, we must develop a new set of ecologic indicators that span the realm of biological organization from genetic markers to entire ecosystems and are broadly applicable across geographic regions while integrating stressor types. We briefly review recent developments in ecologic indicators and emphasize the need for improvements in understanding of stress-response relationships, contributions of multiple stressors, assessments over different spatial and temporal scales, and reference conditions. We provide two examples of ecologic indicators that can improve our understanding of these inherent problems: a) the use of photopigments as indicators of the interactive effects of nutrients and hydrology, and b) biological community approaches that use multiple taxa to detect effects on ecosystem structure and function. These indicators are essential to measure the condition of coastal resources, to diagnose stressors, to communicate change to the public, and ultimately to protect human health and the quality of the coastal environment. Key words: coastal, ecologic, estuarine, health, indicators, marine, nutrients, responses, stressors. Environ Health Perspect 112:979-986 (2004) . doi:10.1289/ehp.6903 available via http://dx.doi.org/ [Online 11 May 2004]

Address correspondence to G. Niemi, Natural Resources Research Institute, University of Minnesota, 5013 Miller Trunk Hwy., Duluth, MN 55811-1442. Telephone: (218) 720-4270. Fax: (218) 720-4328. E-mail: gniemi@d.umn.edu

We thank T. Barnwell for comments on an earlier version of this manuscript. This is contribution number 364 from the Center for Water and the Environment of the Natural Resources Research Institute.

Although the research described in this article has been funded wholly or in part by the U.S. Environmental Protection Agency's Science to Achieve Results (STAR) program through cooperative agreements (R-82867501, R-82867701, R-82867601, R-82945801) to the University of Minnesota, University of North Carolina, Pennsylvania State University, University of California, and the University of Southern Mississippi, respectively, it has not been subjected to the Agency's required peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.

The authors declare they have no competing financial interests.

Received 9 December 2003 ; accepted 10 May 2004.