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Ocean health index devised

Can a single number represent the health of an ocean? Researchers think they have cracked a method to do just that, they reported at the American Association for the Advancement of Science meeting in Vancouver this weekend.

The ‘Ocean Health Index‘, devised by a consortium of more than 60 international scientists, aims to integrate measures of all kinds of ocean fitness, from a water body’s ability to support local jobs to endemic species. The effort is part of a growing movement to quantify ecosystem health in order to help policy-makers set priorities and measure improvements, just as single financial measures, like Gross Domestic Product, compress a mass of complex data into a single number for tracking purposes. “It’s GDP envy” that makes ecologists attempt projects like this, says Ruth deFries, an ecologist at Columbia University in New York who was at the meeting but is not involved with this project.

The index is composed of ten categories: food provision, clear water, natural products (from pharmaceuticals to fish oils), artisanal opportunities (meaning the chance for families or small businesses to fish for themselves), carbon storage, coastal protection, sense of place (a category that accounts for the presence of iconic species or the ‘special’ nature of a place for the local community), livelihood (its contribution to the local economy and jobs), biodiversity, and tourism and recreation. Each category is ranked out of 100 on its present status compared to a reference state, and from –100 to +100 on three factors assessing its likely future state. “That’s a quantification of sustainability,” says Benjamin Halpern, a biologist at the University of California at Santa Barbara and lead researcher for the project. This results in a score for each of the ten measures. The categories can then be weighted (the default is to weight them evenly) and a single number pops out.

Although there are a host of subjective decisions that go in to each assessment, Halpern insists that he and his colleagues tried their hardest to make it as scientific and reproducible a method as possible. Only global data sets are used, so that one site’s assessment will be comparable to another’s. And rules have been set about which data sets and which reference points to use. “I guarantee someone will criticize it for being subjective, but I can’t think of a more objective way to do it,” he says.

Whoever uses the index will have to disclose which data sets they used, what scores they gave and how the categories were weighted, giving a fuller sense of the ocean’s health. “We don’t just need a ‘Dow Jones’, but that plus all the bits you’d need if you were a broker,” says project participant Andrew Rosenberg of Conservation International in Washington DC. “It’s an integrated measure, but it can be unpacked.”

The group has used their methodology to evaluate the exclusive economic zone of every country around the world — and more than once for some countries, such as the United States, which borders on several oceans. These ranked scores, along with a detailed description of the method, are in a paper now undergoing peer review. The assessment was a massive project: the description of how they crunched the data is 120 pages long, says Karen McLeod, a co-author of the work and director of science for COMPASS, a group that helps scientists communicate with policy-makers. They had hoped to unveil the scores at this meeting, but will have to wait for publication before doing that. “In some ways, that’s a good thing,” says McLeod. Once the numbers are out, the team anticipates a lot of squabbling about who deserves a higher or lower score, rather than a sober assessment of the method, she says.

Photo: Vancouver Harbour illustrates the diversity of human-ocean interaction.

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