Goal 14 of the United Nations' Sustainable Development Goals (SDGs) is dedicated to conserving and using the oceans and their resources for sustainable development. We suggest that a 'gross marine product' (GMP) index — a measure of the oceans' natural capital — would be invaluable for achieving this goal.

The seas provide us with food, materials, livelihoods and recreation. Managing these ecosystem services effectively can help us to eradicate poverty, develop sustainable economies and adapt to global environmental changes. Yet international-resource experts and national strategies still focus largely on goods and services delivered by terrestrial ecosystems (see go.nature.com/2bcqjr0).

A GMP index would provide a measure of marine ecosystem goods and services on a national or global scale, derived from estimates for individual oceans. More international research will be necessary to underpin these estimates. The results would inform decision-makers, the private sector and the public on how they could help to achieve goal 14, as well as the 60 targets across most of the 17 SDGs that are relevant to the sustainable development of coastal zones. An integrated programme that measures, monitors and assesses the health of human–ocean systems should oversee their sustainability.