How much is the sea worth?

If the world's seas and oceans were a national economy, how much would they be worth?

Around $24 trillion (£15.7tn; €21.2tn) according to the World Wildlife Foundation (WWF) in a report this month, making it the world's seventh largest economy.

The group drew up the research with the help of Boston Consulting Group and Professor Hoegh-Guldberg of the Global Change Institute in Australia.

The report aims to make policy makers and business leaders view the sea as a common investment.

This technique of auditing nature in financial terms is known as "natural capital". It has been used extensively in global health checks like the Millennium Ecosystem Assessment in 2005, for example.

But there are questions as to how accurate such figures can be when applied to nature, and calculated on this grand scale.

And is monetary value really the best way to measure nature's importance to the planet, and the environment that sustains us?

Video journalist: Dougal Shaw