In the wild worlds of coral reefs, seaweeds and corals are locked in mortal battles and scientists have revealed how overfishing, sewage and farm pollution can tip the balance in favor of the weeds.

Newly published findings from three years of field experiments in the ailing reefs of the Florida Keys have profound implications at a time when climate change is killing corals and threatening the very future of reefs worldwide.

“This study gives very clear evidence that if there is overfishing or eutrophication, the corals are going to be more susceptible to increasing temperature,” said David Kline, a Scripps coral scientist who wasn’t involved with the study, which was published Tuesday in the journal Nature Communications. “That means that marine reserves and controlling and limiting pollution are important.”

More than half of the corals growing in some of the best protected reefs of the Great Barrier Reef were recently found to be dead, following the third and worst coral bleaching on record, which was caused by warm seawater. Coral mortality rates have been even higher in some other places.

Corals provide sanctuaries where young fish can fatten up, supporting large fisheries as well as tourism industries. Coral reefs also protect coastlines from erosion and flooding.

Although warming waters are a global problem, the new study showed that problems under the control of national governments and coastal communities can make global warming far more dangerous for their local reefs.

In the Florida experiments, fatal impacts of pollution and overfishing on corals were worsened when water temperatures rose, such as in summer. After corals succumb and die, their colorless carcasses become covered with mats of algae.