Rebecca Pow is MP for Taunton Deane.

At first sight, you may not realise that the UK seas are home to some of the richest and most diverse marine life in the world. Despite the grey chill of the North Atlantic, our coasts are teeming with wildlife.

Many of these species and habitats, however, are under pressure from human activity. Left alone by people, marine ecosystems renew themselves. But recent generations have been heavy-handed, dramatically depleting wildlife and habitats in ways that make natural recovery impossible. We know that about 90 per cent of large fish are already gone, and that 90 per cent of global fish stocks are over-exploited.

The consequences of this are not just about food security or the odd snorkel in Cornwall. What we forget (even when we are trying to reduce greenhouse gas emissions to mitigate climate change) is that healthy oceans absorb half the CO2 that we produce. So what happens when the planet’s lungs pack up?

Fortunately the UK has a unique chance to make sure we never have to find out. With nearly 18,000 km of mainland coastline, we have the widest range of marine habitats in Europe. And with 14 Overseas Territories, our total marine estate is the fifth largest in the world. We are one of the world’s most significant marine custodians, and are uniquely placed to show leadership on this global issue.

Conservative Environment Network (CEN) MPs recently met with the Secretary of State to make the exactly this case – so I was delighted by the Chancellor’s pledge in the Spring Statement to protect the waters around Ascension Island, one of our Overseas Territories and a biodiversity jewel in the crown. This announcement will form part of the UK’s hugely important ‘Blue Belt’ programme, and is a massive step forward for ocean conservation.

Ascension Island, as Lewis Pugh has pointed out, is a “rare survivor of extraordinary abundance in a sea of decline”. It harbours the second-largest green turtle breeding population in the Atlantic, an entirely unique frigate bird species and some of the largest recorded Atlantic blue marlin. The Atlantic waters around Ascension literally teem with life, in a Biblical way that is foreign to modern generations.

And now it will become the largest marine reserve in the Atlantic. It will become another step towards our goal to establish a Blue Belt of over four million square kilometres of marine protected areas (MPAs).

Heroic organisations brought together by Great British Oceans have pointed out that all this can be protected from just 50p per square kilometre per year. That is a total of just £2 million for the Ascension Island. And included in this price is a critical level of protection for a sustainable local economy that relies on local natural resources. Ascension Island simply could not afford to fund a project like this, despite knowing how important a healthy ocean is to their island economy.

The UK is at the forefront in establishing MPAs, with almost 300 sites established so far. Now we must continue to work closely with our international friends to spread this model through programmes like the Commonwealth Clean Oceans Alliance.

Commonwealth friends have some of the largest coastlines in the world, including Canada at 202,080 kilometers, and Australia at 25,760 kilometers. We need to work with governments, scientists, NGOs, universities and local communities in these countries to spread the idea of a Blue Belt and to safeguard our oceans for future generations.

For it is only by granting special protection that we can properly monitor and measure the full value of marine environments, and incorporate them into all aspects of policy-making. New and improved understanding of our oceans will allow us to demonstrate their vital importance and help us to set new ambitions and global benchmarks. Our new network of MPAs will help oceans to begin to recover their health so that our children and grandchildren can learn how to draw down on the riches of the sea sustainably.

In places as far away as Antarctica, and the Pacific and Indian Oceans, we have a unique opportunity to protect precious marine habitats using local knowledge, world-leading science and global leadership. Yesterday the tide turned on Ascension Island; tomorrow it will turn on the world.