Corals are not dead (yet)

Corals are not dead (yet)

Corals have the ability to survive death. However, their emergency toolkits are now being tested to the limit.

 Illustration of coral bleaching. Kate Furby

Illustration of coral bleaching. Kate Furby

Jan 15, 2018

Coral reefs survived the extinction of dinosaurs. They are 250 million years old. They have seen meteor crashes, ice ages, woolly mammoths, and the movement of continents. But it is carbon emissions that may prove to be the biggest threat of all. Human-induced climate change, coupled with pollution and overfishing, has the future of coral reefs looking grim.

A study published last week in Science put coral death in the headlines again. Dr. Terry Hughes from James Cook University in Australia and colleagues found significant bleaching events have become more common in this millennium. “There’s no hiding from climate change in the ocean,” says Dr. Andrew Baird, one of the study’s authors. This research was a massive effort by an impressive group of scientists, using novel statistical analyses and new data standardization methods to examine coral health. The study is not a review, but a new and critical look at historical and global trends for coral bleaching since the dawn of scuba diving and coral science.

Corals are more than slimy rocks, they are ingenious underwater engineers. A coral is an animal, which builds limestone. Coral creates all of the structures you see on reefs. They live in clear tropical waters, which means there are not a lot of particles and food in the water for the coral to eat. Thus the coral evolved to host tiny microscopic algae inside its body. The algae, like a plant, get energy from the sun and share it with the coral.

Coral bleaching refers to the loss of the algae. Bleaching can happen when the ocean gets too hot, and the relationship between algae and coral breaks down. Without the algae, the coral appears white (therefore “bleached”). While corals can survive without the algae temporarily, if conditions do not immediately improve, they will starve to death.

The study combined scientific observations (at 70 out of 100 locations) with the publication record (349 reports). The scientists then created clear categories for coral health and defined parameters for analysis. The result is the cold details for coral reefs today. If 14th century Italian bubonic plague doctors had been able to gather and analyze big data and visualize global trends, could they have changed the course of history? By taking a long term and global look at the health of corals, marine biologists hope to predict and change the future of reefs.

Corals grow slowly and need time to recover from big bleaching events. “The return times between bleaching events is getting to the point at which full recovery is almost impossible,” stated Dr. Baird. These damaging events may now happen every six years, instead of the historical 30-year frequency. The ability to recover from stress is the corals’ most valuable tool. It is responsible for the long-term persistence of coral reefs through geological time. Similarly, forest fires can destroy habitat, but after a few years the area begins to recover. If fires raged every other year, a once thriving ecosystem would be remain charred rubble. This new analysis of coral reef bleaching and recovery suggests our oceans may be entering an era of rubble.

The report examined how bleaching events have affected different parts of the planet. Coral reefs occur in tropical areas around the world. Each ocean basin has a unique natural history and pattern of coral bleaching, which translates into different parts of the globe being affected in different ways. The Atlantic has long since felt the impact of humans, and now the Pacific is starting to show increasing signs of human impact as well.

“Areas that have so far escaped severe bleaching are likely to decline further in number,” the authors state, “and the size of spatial refuges will diminish.” Worldwide expansion of impacted areas, increased frequency and severity of coral bleaching and death. Grim future predictions. It sounds hopeless.

If there’s one thing we could do for coral reefs, Dr. Hughes and his coauthors urge us to make serious moves to reduce carbon emissions. Everyone on the planet, even those living far from the coast, have the ability to make a difference. Call your representatives about their climate policies. Consider your own energy usage and commuting options. Hug a scientist. We could all use a little less energy and a little more hope.