wildlife populations. More than 50% of U.S. marine fisheries exploit species that are estuarine- 
dependent at some life stage, and many estuarine fisheries are in decline due to combined effects 
of over fishing, habitat alteration, and pollutants (Houde and Rutherford 1993). Virtually all 
Great Lakes fish depend at least indirectly on coastal wetland habitats, where habitat alteration is 
an important threat (Whillans 1992). Within these priority ecosystem types, OW has a particular 
interest in vegetated habitats. Aquatic vegetation is not only a key habitat for many wetland, 
estuarine, and coastal species, but also a key mediator of stressor effects on aquatic biota and a 
primary response variable for anthropogenic stressors such as nutrient and sediment loading. The 
combination of OW interests, pressures affecting societally and ecologically important ^cies, 
and NHEERL research expertise leads to a focus on these endpoints in the this plan. 
Assessing the ecological consequences of habitat alteration has been called one of the most 
challenging scientific problems and environmental policy issues confronting society (NRC 1997, 
Rapport et al. 1998, EPA 1990). The importance of habitat quality and quantity for maintaining 
species is indisputable, but quantifying exactly how species depend on habitats is multi-faceted 
and complex. Habitat provides a wide array of species life-support functions, ranging from 
providing shelter, substrate, and appropriate physiological conditions; to mediating natural 
disturbances and anthropogenic stressors; to maintaining food webs by hosting primary and 
secondary production. Consequently, habitat alteration can degrade diversity, food-web 
structure, ecosystem function, and populations of valued fish, shellfish, and wildlife species via 
complex effect pathways. Mobile and migratory species can use multiple habitats to meet 
developmental requirements or sustain local populations, and "habitat” for them may refer to a 
combination of quantity, quality, extent, and arrangement of different habitat types at a variety of 
spatial scales. Many stressors interact with aquatic systems in ways that alter the normal spatial 
distribution or mosaic of habitat patches, with important implications for ecosystem function and 
dependent fish, shellfish, and wildlife populations. More generally, successful preservation of 
biological diversity and ecosystem structure and function requires protection of multiple habitats 
within a landscape framework and not merely individual habitats in isolation. For many 
important aquatic habitats, there is little quantitative information on the relationship of habitat to 
dependent biota; in particular how changes in habitat quality influence the well being of fish, 
shellfish, and wildlife populations. Finally, broad biogeographic gradients affect the responses of 
ecosystems and biota to habitat alteration. For all these reasons, it is a significant research 
challenge to quantify the life support functions of specific habitats and habitat complexes in 
sufficient detail to predict the biological effects of both incremental and catastrophic habitat 
alteration. 
NHEERL has initiated a nationwide research program to quantitatively link alterations in key 
habitats to fish, shellfish, and wildlife endpoints because habitat alteration is such an important, 
pervasive stressor on valued aquatic resources. The research involves all four Ecological 
Divisions of NHEERL and spans the coastal resources of the East, West, Gulf states, and the 
upper Midwest. NHEERL will enter into partnerships with other management agencies and 
research entities as appropriate to further these research goals. The research described in this 
plan will help build the scientific basis to implement regulations and policies to protect aquatic 
populations and the ecosystems upon which they depend. 
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