Russia and Ukraine look likely to block a plan to create two huge marine reserves off the coast of Antarctica that combined would be bigger than the area of all the world's protected oceans put together.

The 25-member Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) meets in Bremerhaven, Germany, on Thursday to discuss the proposal to create the Marine Protected Areas (MPAs) in the Ross Sea, off the east coast of Antarctica. A decision, expected on Tuesday, would require unanimous agreement.

The proposal, backed by the US, New Zealand, Australia, France and the EU, would designate an area 13 times the size of the UK as one in which natural resource exploitation, including fishing, would be illegal. Advocates say the MPAs would provide environmental security to a region that remains relatively pristine.

Publicly, delegates and environmental NGOs have expressed optimism that the meeting will be a success. But a senior source at the meeting said the attitudes of Russia and Ukraine as they entered were looking negative.

The debate highlighted a rift between "pro-[fish]harvesting countries" and those who style themselves proponents of conservation, such as the US, Australia, New Zealand and the EU, according to Alan Hemmings, a specialist in Antarctic governance at the University of Canterbury, New Zealand.He said: "You would put Russia and the Ukraine near the top of the states that are likely to be concerned about marine protected areas in the Antarctic on a large scale, along with China, Japan and, on and off, South Korea."

"There's a tug of war between those who want to establish conservation management and those who want to keep working with smaller-scale fisheries management," said Steve Campbell, campaign director at the Antarctic Ocean Alliance. But he expressed "quiet optimism" that the proposals would be passed, if not at the meeting in Germany, then at the next annual meeting in Hobart, Australia later in the year.

The US and NGOs have been lobbying countries who expressed reservations at the last CCAMLR meeting. NGOs and delegates reported that China, South Korea and Japan looked likely to support the proposals.

Many countries have valuable fisheries in the region, particularly for patagonian toothfish and krill. Andrea Kavanagh, director of the Pew Charitable Trusts Southern Ocean sanctuaries, said defining the boundaries of the reserves to balance ecology and economic interests would represent a challenge to negotiations.

Additionally, a sunset clause for the reserves, proposed by Norway and supported by Russia and Japan, would mean the protected status of East Antarctic and Ross Sea reserves would have to be renewed in 2064 and 2043 respectively. Campbell said reserves with time limits were highly unusual.

"Precedent tells you that if you set up a protected area, you set it up for an indefinite period of time. If you set up a national park in a country, you designate it in perpetuity." He said the potential for fishing and other resources in the future was driving the push.

"It's not just about what's there now, it's also about what could be a future economic interest or a future interest in the region," said Campbell.

The extraordinary session in Bremerhaven was arranged after the last annual meeting of CCAMLR in November, 2011 failed to reach a consensus on the MPAs. At the time Russia, China and Ukraine expressed concerns at a lack of available science in favour of the reserves. The decision was taken to reconvene this summer with the agenda solely focused on the proposals.

Green groups expressed dismay at last year's inaction. They were joined by delegates from the USA, UK, EU and Australia who feared that CCAMLR had lost its proactive attitude to conservation.

At the end of the 2011 meeting, the Ukraine delegation said well-grounded scientific arguments were lacking. They said MPAs were only one approach to managing an ecosystem and that "only fishing, at least at some level, can guarantee that research is conducted" to monitor fish stocks.

"Russia was of the view that previous scientific committee advice was related to only some aspects of MPAs and that all available information needed to be considered," said the Russian delegation.

Russian and Ukraine declined to comment further on this week's meeting.