New Zealand marine scientists have been significant contributors to the 10-year Census of Marine Life through specific research projects and missions such as the 2009 survey of biodiversity in the Ross Sea, which was linked to the International Polar Year, focusing on climate change.

Associate professor Mark Costello of Auckland University's department of marine sciences co-authored an overview paper based on the 25 regional reports released this week, which warns of the threats to marine biodiversity.

Over-fishing was reported to be the greatest threat to marine biodiversity in all regions.

The paper says habitat loss poses a similar threat in several regions, while pollution is the third biggest threat.

Over-fishing depletes targeted fish stocks and bycatch species including seabirds, turtles and mammals.

Marine habitats are being lost to urbanisation, sediment run-off and eutrophication from nutrients such as sewage and agricultural fertiliser.

Climate change poses threats from warmer water temperatures, ocean acidification, and rising sea levels. Biodiversity is already responding to some of these changes, says the study.

The census was backed by the Alfred P. Sloan Foundation, a United States philanthropic group, and will culminate with final papers in October. But if the estimate that the oceans contain about 1.4 million species is correct, that means only a quarter have been identified. So what happens next?

Costello says scientists will continue to add information to the census database. He says knowledge to date has come largely from work that countries were already funding, so it should continue.

What the census did was introduce international collaboration and lend co-ordination to marine biodiversity research.

Project funds allowed scientists to meet and helped to build an open-access database, the Ocean Biogeographic Information System (Obis), which will continue to grow.

Costello says the project highlighted the value of basic taxonomic research and the need for scientists to undertake unglamorous work such as species identification guides. This is vital when it comes to detecting invasive species and other threats.

"There is much we still need to know but there is now a large pool of people to draw information from."