Of the 220 regions scored in 2013, the ocean around the remote Heard and McDonald Islands in the southern Indian Ocean was the most healthy, closely followed by other remote ocean regions in the Pacific and Atlantic. Seas near war-torn developing countries, such as Angola, Liberia and Democratic Republic of Congo, languish near the bottom of the rankings. However, new research proposes improvements to the way that the ocean health index is calculated.

Halpern and his colleagues defined 10 ocean-related societal goals, such as harvesting seafood sustainably, preserving habitats that absorb carbon, and sustaining jobs and thriving coastal economies, to represent the ecological, social and economic benefits of the ocean. They then calculated the ocean health index by taking the weighted arithmetic average of these goals. But what Halpern and his colleagues didn’t take into account is that improvement in one area can sometimes be to the detriment of another.

Using a more familiar example, Wilfried Rickels from the Kiel Institute for the World Economy in Germany demonstrates how this kind of aggregation of scores can be problematic. “Imagine you have breakfast in the morning where you like to enjoy coffee, bread, jam, ham and eggs,” he says. “Certainly, your well-being from this breakfast would not change much if you had a little bit less coffee but instead a little bit more jam. However, if you are asked to give up further coffee for more jam you would at some point start to have less well-being and would no longer be willing to give up more coffee. In the extreme case it could even be that you have no well-being from breakfast at all if there is no coffee, no matter how much jam, ham or eggs.”

When it comes to natural resources and ecosystems a good balance is often more important than excellence in one area. For example, countries that have created high dykes to protect coastlines from erosion might score highly on the “coastal protection” aspect of the index, but those same dykes may be detrimental for biodiversity. With this in mind, Rickels and his colleagues decided to look further into the problem of how various stocks, assets and goals are aggregated, and assess how it might affect the rankings of the ocean health index.

With this concept of stronger sustainability (i.e. fewer substitutions allowed between the different goals), Rickels and his team found that the overall health score of the ocean decreased and some of the individual rankings changed substantially. In particular, countries that had very unbalanced scores, including Greenland, Russia and Cuba, fell down the rankings table considerably. Meanwhile, countries with a balanced scoresheet, including New Zealand, Thailand and the Falkland Islands, which were often only mid-ranking in the Halpern index, would achieve a higher score under the new system.

“According to our metric, the improvement in the worst performing goal is more important than the deterioration in a rather good performing goal,” said Rickels, whose findings are published in Environmental Research Letters (ERL).

Rickels and his colleagues applaud and admire the work that Halpern and his team put in to constructing the ocean health index in the first place and are careful to stress that they think this index is a great starting point for assessing and improving the health of the world's oceans. However, they believe it is important that the way the scores are aggregated needs to be altered, and they hope that their suggestions will be taken into account.

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