Coral reefs have been called the rain forests of the ocean because of their vast biodiversity and genetic wealth. And over the last few years we have seen a massive die-off of these ecosystems, with a quarter of the world’s reefs already gone. Surveying the destruction, the marine biology community has launched an all-out effort to restore the reefs to health. But first biologists must understand the sources of destruction, from global warming to overfishing and attacks by predators and diseases.

The man-made part of the disaster, caused by burning fossil fuels, has increased ocean temperature an average of 1.33 degrees Fahrenheit since the start of the Industrial Revolution, according to a study in Science. That slight warming is enough to kill some microalgae needed to help the reefs calcify and stay strong. What’s more, the study, led by a team at the University of Queensland in Australia, says that CO₂ released in the course of coral death not only raises temperatures but also makes the water acidic, leaving the reefs brittle and vulnerable to predator attack. Marine biologists point to the example of Carysfort Reef off the coast of Florida: In 1975 it was healthy. By 1985 it was visibly sick. Today it is dead.

Overfishing also presents a risk. Healthy populations of fish eat seaweed, keeping the plant in balance. As fish populations have diminished, seaweed has increased, fed by human sewage. Without enough fish to eat the seaweed, the seaweed strangles the coral reefs.

Only when we understand the reefs’ complex, interwoven problems will we be able to save them, says University of Miami marine biologist Andrew Baker. In one potential solution, Baker aims to boost the production of a type of microalgae adapted to thrive in warmer temperatures. Others are hoping to find temperature moderators—such as a certain species or geologic feature—that might protect reefs from the heat even as temperatures rise.

Until permanent solutions are found, the nonprofit Reef Relief’s Coral Nursery Project plans to collect dislodged coral colonies and transplant them to a nursery. When the corals are healthy, they will be returned to the oceans to help colonies flourish once again.

by Sherry Baker - Discovery Magazine