Global human impact map
©BS Halpern
World map showing Man's effect on the planet's oceans

Almost half of the world's oceans have been seriously affected by over-fishing, pollution and climate change, according to a major study of man's impact on marine life.

An international team of 19 scientists have published the first ever comprehensive map showing the combined impact of human activity on the planet's seas and oceans.

It shows that more than 40 per cent of marine regions have been significantly altered, while just four per cent remains in a pristine state.

Previous studies have largely focused on the impacts of specific activities such as pesticide runoff or fishing, or have looked at damage in certain areas.

The North Sea is one of the most heavily affected regions, along with the South and East China Seas, the Caribbean, the east coast of North America, the Mediterranean, the Red Sea and the Persian Gulf. The least affected areas are near the poles.

Dr Ben Halpern, of the University of California, presented the new findings at the American Association for the Advancement of Science (AAAS) conference in Boston.

Dr Halpern said: "This project allows us to finally start to see the big picture of how humans are affecting the oceans. The big picture looks much worse than I imagine most people expected. It was certainly a surprise to me."

Activities and impacts included in the study include fishing, ocean acidification caused by pollution, temperature change, species extinctions and invasions, and the shipping, oil and gas industries.

The researchers developed models to quantify and compare how 17 human activities affected marine ecosystems. For example fertiliser runoff has been shown to cause significant damage to coral reefs but has less effect on kelp forests.

They gathered data from across the world and collated the results to give each area a score for man-made damage and changes.

The results, published in the journal Science, show that 41 per cent of the world's oceans and seas have been significantly affected by multiple human activities.

Coral reefs, seagrass beds, mangroves, rocky reefs and shelves are among the most seriously altered ecosystems.

Areas worst affected by human impact
Maps showing the marine areas hardest hit bay the affect of Man

The team hope their work will provide information to help policymakers decide on priorities for conservation action.

Dr Kimberly Selkoe, of the University of Hawaii, said: "Conservation and management groups have to decide where, when, and what to spend their resources on.

"Whether one is interested in protecting ocean wilderness, assessing which human activities have the greatest impact, or prioritising which ecosystem types need management intervention, our results provide a strong framework for doing so."

Coastal regions were shown to be particularly badly hit. The North Sea was the 24th most affected region of 232.

The effects of over-fishing in the North Sea have been well-documented, while the close proximity of heavily populated areas, shipping, oil and gas extraction have all affected a region that is relatively shallow and enclosed, and therefore slower to repair damage.

Co-author Dr Mark Spalding, a marine scientist at the conservation group Nature Conservancy, said: "What is surprising is the truly global spread of human impact.

"But it's not all doom and gloom. In some areas, such as the Great Barrier Reef, strong integrated conservation measures are being introduced.

"The map provides a challenge for us to start to think seriously about conservation and management, and gives us pointers to the priorities and different states of urgency of response required."