Katharina Fabricius studying a crown-of-thorns starfish.

For the third time since the 1960s, scientists have noted that the Great Barrier Reef is under siege. Repeated outbreaks of the crown-of-thorns starfish have been destroying large parts of the reef and scientists are racing to understand why. Are these population explosions part of a natural cycle? Or could human activity be to blame? While theories for the outbreaks abound, marine biologist Katharina Fabricius and her team, including Jon Brodie and Glenn D'eath, are finding evidence suggesting that these repeated outbreaks could be related to nitrogen-rich agricultural runoff.

Nitrogen is one of the great triumphs in the history of food production. But only recently have its unintended consequences started to become visible. Areas known as dead zones resulting from too much nitrogen are on the rise worldwide. In Queensland, nitrogen from sugar cane fertilizer and from range animal manure gets flushed off the field during tropical storms. Flowing into creeks and rivers, it makes its way to the reef. According to scientists, it can act as fertilizers — sparking the growth of certain types of algae — which are just the right size to be eaten by crown-of-thorns larvae.

Fabricius and her colleagues have been correlating storms and river runoff with hydrodynamic models of current flow along the reef. This is no easy task. More than two dozen rivers flow into the long stretch of coastal waters swirling with complex currents. They've found that starfish distribution corresponds to outbreaks that began years earlier at the nitrogen hotspots.

Vince Vitale walking through a sugarcane field.

Given the growing awareness of coral reef sensitivity to nitrogen, what solutions are being tested? Vince Vitale, a cane farmer from Queensland, Australia has found a solution by looking back to a day when less runoff came from the fields. Back in the 1880s, trees and marshes then served as a natural barrier that kept runoff from flowing into the river. Today, farmers and ranchers have cleared trees right up to the riverbanks; only a thin band of trees remains, not nearly wide enough to sop up farm chemicals before they reach the water. Vince has decided to give up two and a half acres of crop land to plant trees along the river. "I could have probably made myself an extra... maybe 1500 dollars a year... but I'm prepared to let that go... to me it's a shot in the arm for the effort. I go down there and walk among my trees and say, I created this. I love this. It makes me feel good. And feeling good is a good thing. A person might live longer that way."

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