What would happen if all the coral reefs died off?

We’re currently facing the worst bleaching of coral reefs ever known in history, but what would happen if all the coral reefs died off? We’ve already lost 50% of the world’s coral, and we’re at risk of losing even more. If the world lost all its coral reefs, the results would be dire.  As coral continue to be assailed from all sides, the question becomes: what happens to a coral reef when the coral disappear?

To get an idea, says University of Queensland ecologist Peter Mumby, look to Jamaica. In the 1970s, the Caribbean nation’s vibrant coral populations died. In their place grew seaweed forests.

Jamaica’s coral reef collapse was a complex process that started with decades of heavy fishing. In the decades leading up to the 1970s, overfishing depleted the region’s fish, including those that eat seaweed. With the fish gone, urchins gorged on the sudden abundance of algae.

But in 1980s, disease struck the urchin population. The urchins died en masse, leaving too few herbivorous animals to keep the seaweed in check. Over the span of a year, the seaweed population soared and began smothering the coral, which were also declining because of disease.

Even a healthy reef will sometimes collapse because of a natural disaster such as a tropical cyclone. In such cases, an “algal turf”—a layer of small algae—begins to grow over the dead coral. In healthy environments, fish will return to the destroyed reef to feed on the algae and, after a few years, the coral will recover.

But in a recent experiment, Mumby and his team studied what happens to a damaged reef when herbivorous fish are unable to repopulate the area, which is what happened in Jamaica’s coral collapse. They found that when large, algae-eating fish such as parrotfish are prevented from recolonizing the reef, the growth of new corals is decreased by 700 percent. When all fish are excluded from returning to the reef, coral growth drops 1500 percent. And in the corals’ place: seaweed.

Seaweed forests lack the complex physical structures of coral that fish need to thrive. Without coral reefs, fish can’t hide from predators and become easy prey.

The transition from vibrant coral reef to seaweed forest experienced in Jamaica foreshadows the large-scale deterioration of coral reefs that could result if global and local pressures such as pollution, overfishing, and ocean warming continue. Theoretically this ecosystem transition is reversible, but only if the pressure that caused the decline goes away.

Sea life has the most to lose. Coral reefs cover less than 1% of the ocean floor. But, they provide an essential ecosystem for a quarter of all marine life. One of these creatures — a type of sea slug — is actually an important ingredient in certain cancer-fighting compounds.

In fact, some estimates predict we are 300 to 400 times more likely to find new drugs from coral reef ecosystems than land-based ones. But that’s only if they survive the next century.

The US fishing industry supports 1.5 million jobs alone, nearly a quarter of what the US meat and poultry industry employs. Without reefs, billions of sea life species would suffer, millions of people would lose their most significant food source, and economies would take a major hit. But it’s not just about the jobs.

Coral reefs attract tourists to more than 100 countries and territories worldwide. These tourists spend billions of dollars diving into the underwater landscapes.

Without these attractions, economists estimate that coastal-tourism would drop more than 9%, which is equivalent to about $36 billion.

These reefs also provide protection to the tourist-reliant coastlines. They act as natural barriers, canceling out 97% of a wave’s strength and protecting more than 200 million people. Building seawalls for the same protection costs $2.5 million per mile.

But today humans are putting these all at risk. Rising ocean temps and pollution stress the coral, which can kill entire coral ecosystems within just a few months. If we do nothing to cool the oceans, the planet’s remaining coral could all be wiped out.

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