LONDON, April 20 (Xinhua) -- The biggest ever action plan to help preserve the world's oceans was agreed in London on Friday at the Commonwealth Heads of Government meeting.

The two-day conference concluded at Windsor Castle with a communique outlining what the 53 members of the Commonwealth had agreed.

As well as action on the oceans, cyber crime and global health, the meeting also agreed on an Intra-Commonwealth Trade and Investment strategy that will see trade between Commonwealth members rising to 2 trillion U.S. dollars by 2030.

The meeting also agreed that Queen Elizabeth II will be succeeded as head of the Commonwealth when she dies by her son and heir to the British throne, Prince Charles, the Prince of Wales.

The communique highlighted the close linkages between the ocean, wellbeing and prosperity of the people of the Commonwealth, and recognized the opportunities for sustainable economic development from the ocean and coasts.

It expressed alarm at the deteriorating health of the world's oceans, which impacts every country and poses an existential threat to many Commonwealth communities.

Government heads identified climate change, including sea level rise and acidification, biodiversity loss, overfishing, and plastic pollution as some of the most significant pressures on the ocean, and called for ambitious, coordinated global action.

They adopted the Commonwealth Blue Charter, setting out the principles by which Commonwealth members will lead international efforts by sustainably developing and protecting and safeguarding oceans for future generations.

The communique said: "Heads agreed to establish Action Groups on ocean issues led by Commonwealth member countries, which will collaborate with partners at national, regional, and international levels, in addressing identified priority ocean issues of member countries."

In a speech at the closing ceremony, British Prime Minister Theresa May said: "This is the first time that security has been a central theme of our leaders' meeting. And we have shown our resolve to stand together in defense of the rules based international system, and in defiance of those who threaten us all by seeking to undermine it."

May said the Commonwealth Cyber Declaration will help protect people and businesses from ever-more sophisticated digital threats, and counter those who would abuse the freedom of the internet to undermine values, security and even democracies.

The summit meeting also pledged to ensure that all girls and boys across the Commonwealth will be able to access at least 12 years of quality education and learning by 2030, said May.

Britain assumes the chair of the Commonwealth for the next two years, with the next heads of government meeting in 2020 in Rwanda.