We regularly hear calls to improve “ocean health.” Health is a powerful metaphor, but scientists have had no way to measure it and therefore no means to evaluate how the world's oceans are doing. More than 60 researchers from a cross section of disciplines and institutions, including the National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California, Santa Barbara, have created the Ocean Health Index to do just that. It rates the health of ocean waters bordering 171 coastal countries and territories. Each nation's overall score is the average of scores for 10 widely held public goals for healthy oceans, including sustainable food provision, recreation, fishing opportunities and biodiversity.

The index, which was published in August in Nature, is not a measure of how pristine the ocean is. (Scientific American is part of Nature Publishing Group.) Instead it measures how sustainably the ocean is providing the things people care about. The goals are universal measures of ecosystem health—all 10 must be met for a country's ocean to be rated as healthy—but the relative importance of each goal can vary from place to place.

Factoring human goals into assessments of ocean health is a radical departure from traditional conservation approaches. Yet public policy and conservation organizations worldwide are rapidly converging on the view that people are now a fundamental part of every ecosystem on the earth, and any effective management strategy must embrace this reality. If we focus only on excluding people from nature, conservation plans are doomed to fail.

The index is an important first step. Countries cannot make progress on ocean health without first knowing where they stand. In that sense, the index is a key benchmark. Later this year the NCEAS and various partners will test its application in the U.S., Fiji and Brazil. Policy makers and managers could use the index to guide decision making—for example, about whether offshore wind energy should be expanded in the U.S., whether land or ocean conservation measures will benefit coral reefs in Fiji and how marine-zoning plans in Brazil might affect overall ocean health.

Of course, various people or adjacent countries might put different priorities on different goals. As a tool that lays them all out, the index can aid any negotiations by identifying trade-offs and synergies.

» For an article that addresses controversy over the index, see "A New Goal for Nature: Healthy, but Not Pristine" by Benjamin S. Halpern.

Interactive by Krista Fuentes