Pressure is mounting on the Baird government to declare Sydney Harbour and surrounding coastal regions a marine park in a bid to limit the impact of an increasing population and a warming climate.

The future of the harbour will be one item for the World Parks Congress, a once-in-a-decade event that opens in Sydney on Wednesday and has lured more than 5000 delegates, including 30 environment ministers, from 167 countries.

A flotilla of traditional Pacific islander canoes will paddle up the harbour for the opening, bearing the leaders of Kiribati, Cook Islands and Palau. Some of the canoes will have journeyed 6000 nautical miles (11,100 km) to highlight the threats posed by climate change and overfishing.

While the government has unveiled a new national park protecting wetlands and additions to several other parks, researchers, Labor and green groups are calling for priority to be given to protecting the marine environment in and around Sydney Harbour.

Emma Johnston, inaugural director of the Sydney Harbour Research Program at the Sydney Institute of Marine Science (SIMS), said protection should be granted to the Hawkesbury-Nepean bioregion stretching from the Hunter to Wollongong.

"We very much support the process of zoning a bioregion like Sydney Harbour," Professor Johnston said. "This is the only bioregion [in the state] that doesn't have a marine park."

On Tuesday, Professor Johnston told a workshop linked to the congress that Sydney's population would swell from 4.6 million to 7 million by 2050, adding demands on waterways.

"We need to protect more of our fragile coasts to accommodate that [rising population]," said Kevin Evans, chief executive of the NSW National Parks Association. "We have been calling on the government to begin the process to declare a marine park within the Sydney region."

Such a process would need two years to consult with communities and for scientists to determine which areas should be "no take" areas barring recreational fishing, Mr Evans said.

But the government won't be announcing any marine parks during the congress, a spokesman for Environment Minister Rob Stokes said. Research on the issue is being undertaken by the NSW Marine Estate and SIMS, he said.

In September, Labor announced that if elected at next year's elections it would create a Sydney Marine Park stretching from Pittwater to Port Hacking, including the harbour, Botany Bay and Parramatta and Lane Cove rivers..

"Sydney Harbour is an icon. We want to protect it for both conservation values and recreational fishing," Luke Foley, the shadow environment minister, said. The harbour alone has triple the number of fish species recorded as the entire UK coast.

The Greens also back the call: "Sydney has one of the richest marine environments in the world, with over six hundred marine species making Sydney harbour their home," said Mehreen Faruqi, the party's spokeswoman for the marine environment.

Mr Stokes will launch the World Harbour Project at the congress on Monday. The program led by SIMS, aims to help ports around the world deal with increasing environmental challenges.

With 80 per cent of Australia's population located within 50km of the coast and many projects planned to expand ports in the country, it is vital lessons learned from Sydney are applied here and overseas, Professor Johnston said.

"We've seen remarkable improvements in water quality and ecosystem integrity [in Sydney Harbour] over the last 20 or so years," she said.

New threats, though, are emerging as climate change triggers a strengthening of the East Australian Current, bringing warmer waters – and new invasive species – further south. Rising carbon dioxide levels are also changing the chemistry of the sea.

Still, Australia's challenges pale compared with some other ports taking part in the World Harbour Project, such as China's Shanghai and Qingdao.

Shanghai has just completed two 50 km-long jetties, while land reclamation around Qingdao has shrunk the area around adjacent Jiaozhou Bay by a third since 1928, limiting the sea's ability to flush out pollutants and silt.

"It's not too late ... we have to learn how we've managed or mismanaged these developments," Professor Johnston said.

Since most port expansions result in a hard substrate replacing soft sediment or submerged aquatic habitats, designers have to ensure "ecological engineering" at least minimises the impacts.

"How do we recreate natural systems or at least build in ecological functions and not just engineering functions into our port developments?" she said.

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