planet earth - wake up call - oceanic decay

Fishing, climate change and pollution have left an indelible mark on virtually all of the world's oceans, according to a huge study that has mapped the total human impact on the seas for the first time. Scientists found that almost no areas have been left pristine and more than 40% of the world's oceans have been heavily affected.

"This project allows us to finally start to see the big picture of how humans are affecting the oceans," said Ben Halpern, assistant research scientist at the University of California, Santa Barbara, who led the research. "Our results show that when these and other individual impacts are summed up the big picture looks much worse than I imagine most people expected. It was certainly a surprise to me."

The study found that almost half of the world's coral reefs have been heavily damaged. Other concerns rest with seagrass beds, mangrove forests, seamounts, rocky reefs and continental shelves. Soft-bottom ecosystems and open ocean fared best but even these were not pristine in most locations. Previous studies of human impacts have focused on a single activity or on an isolated ecosystem, and rarely on a global scale.

Fiorenza Micheli, an associate professor of biology at Stanford University, said the maps should guide ocean management in future. "By seeing where different activities occur and whether they occur in sensitive ecosystems we can design management strategies aimed at shifting activities away from the most sensitive areas."

To make the map scientists compiled global data on the impacts of 17 human activities including fishing, coastal development, fertiliser runoff and pollution from shipping traffic. They divided the ocean into one-square-kilometre cells and worked out which human activities might have touched each particular cell. For each cell, the scientists allocated an impact score to look at the degree to which human activities affected 20 types of ecosystems. Around 41% had medium high to very high impact scores. A small fraction, 0.5% but representing 2.2m square kilometres (850,000 square miles), were rated very highly affected.