A healthy ecosystem is one that is intact in its physical, chemical, and biological components and their interrelationships, such that it is resilient Ð can withstand change and stressors. It is a system that is not experiencing the abnormal growth or decline of native species, the concentration of persistent contaminants, or drastic anthropogenic changes to its landscape or ecological processes. A healthy and diverse ecosystem is one that provides abundant and beneficial services to its constituents, such as food, water, shelter, economic livelihood, recreation, and natural beauty. Further information on the concept of ecosystem health can be found at the website of the International Society for Ecosystem Health.

An ecosystem is composed of plant and animal communities and the physical environment in which they live. The practice of ecosystem health is the investigation of the components of an ecosystem which render it adaptable and resilient enough to withstand perturbation, and then both the transfer of that understanding to ecosystem stewards, who use the information to enact appropriate policies and actions, as well as the transfer of questions and needs for information from the stakeholders to the scientists.

Improving and maintaining ecosystem health can be likened to the DNA double helix. The DNA double helix consists of two intertwining strands, each strand composed of complementary molecular building blocks, and the two strands held permanently intertwined via chemical bonds, or "glue". The DNA double helix encodes the instructions for the components and processes of all living things. In a similar way, the ecosystem health double helix consists of one strand, Science, and another strand, Action, bound together into a helix via Translation, the "glue". The ecosystem health double helix thus encodes both the scientific information, and the tools and methods for reversing and amending severe stressors on an ecosystem, whether it be marine or terrestrial.

Targeted ecosystem health programs of the UC Davis Wildlife Health Center, like the SeaDoc Society, function as the Science Strand, and as the Translational Glue that bridge the gap between science and action. In cooperation with stakeholders—governmental and non-governmental organizations, and citizens—whose activities comprise the Action strand, the SeaDoc Society provides sound scientific knowledge for developing effective regional marine conservation strategies. Providing science that will drive and sustain appropriate and effective action is the heart of the SeaDoc Society.

Disease, injury, and nutritional stress are normal causes of wildlife mortality. Under certain circumstances, unfavorable environmental conditions like poor habitat quality, lack of forage or prey, over-extraction of natural resources, unnatural species interactions, or contaminants also can threaten the health of wildlife populations and potentiate wildlife diseases.

Following are examples of this connection between an environment degraded by the aforementioned processes, and the occurrence of disease and mortality in wildlife.

	Bighorn sheep populations have frequently suffered outbreaks of fatal disease due to pathogens carried by domestic sheep. Increasing urbanization has reduced habitat available for both wildlife and ranching of livestock. As a consequence, wildlife and livestock intermingle, and diseases are transmitted between them.
	Native trout in many rivers of the intermountain West are now infected with a parasite (Myxobolus cerebralis) inadvertently introduced into the wild by man, from trout hatchery operations.
	The Southern sea otter population off the coast of California suffers from a number of diseases caused by pathogens heretofore only known in terrestrial animals. Many believe that the influx of human and animal waste into the nearshore coastal ecosystem introduced these pathogens into this endangered species population.
	Despite tremendous success in bringing the black-footed ferret back from the brink of extinction, biologists are struggling with finding suitable release sites in which to reintroduce captive-raised ferrets. Ferrets depend on prairie dog towns for suitable habitat, and introduced diseases and purposeful extermination by man have decimated prairie dog populations.

The Wildlife Health Center focuses its efforts on wild animals in the context of their ecosystems, recognizing that without a healthy place to live, wildlife populations and humans can not coexist.

For more information on the link between wildlife health and ecosystem health, visit the Alliance of Veterinarians for the Environment (www.aveweb.org)