Seaweed-Munching Crabs May Help Save Coral Reefs

Caribbean king crab. (Credit: Angelo Spadaro)

(CN) — While the health of coral reefs around the world has been on the decline for decades, new research revealed Thursday suggests that they may have found an unlikely ally capable of turning the tide on coral reef decay: Caribbean king crabs.

Of all the creatures and marine ecosystems that have experienced firsthand the consequences of climate change and pollution, few have been rocked as hard as coral reefs. 

For years, these underwater marvels have suffered from massive amounts of coral coverage loss as a result of changing water temperatures, aggressive fishing practices and even underwater diseases, leaving many to worry for the future of these coral colonies.

What’s more, the problem with coral reefs is not just limited to their diminishing health and size; it’s also what is taking their place. As a coral reef diminishes, rampant amounts of seaweed invade the space where the coral once thrived, making it even more difficult for coral reefs to bounce back.

Now, however, researchers report that they have come up with a potential solution to this pesky seaweed problem, a solution that relies heavily on the seaweed-heavy diet of one special crustacean.

In a study published Thursday in the journal Current Biology, researchers reveal that after decades of studying coral reef habitats, one of their strongest natural tools in reversing coral reef decline rested with the Caribbean king crab. 

This is because these largely nocturnal creatures can consume massive amounts of seaweed on a regular basis, capable of eating at rates that can rival almost any other Caribbean marine species. They also tend to eat types of seaweed that other underwater dwellers avoid, making them ideal candidates to remove unwanted amounts of the underwater vegetation.

Despite being so well suited to the task, however, researchers determined that there are simply not enough of them naturally occurring around coral reef areas to help keep seaweed growth under control. This led the researchers to wonder just how much a difference crabs could make on the health of the environment if they manually introduced a host of new Caribbean king crabs to a coral reef ecosystem.

Mark Butler of Florida International University said that after researchers put this idea to the test using coral reefs off the Florida Keys, the results were nothing short of impressive.

“Experimentally increasing the abundance of large native, herbivorous crabs on coral reefs in the Florida Keys led to rapid declines in seaweed cover and, over the course of a year or so, resulted in the return of small corals and fishes to those reefs,” Butler said with the release of the study. “This opens up a whole new avenue for coral reef restoration.”

Researchers made the discovery by conducting experiments in 12 isolated sections of a coral reef, with each of the sections falling into one of three distinctive groups: coral reef sections that were stocked with fresh crab, sections that were stocked with fresh crab but not before divers scrubbed as much algae and seaweed from the coral reefs first, and sections that were left completely untouched.

After waiting roughly a year to see how the coral reefs accepted these changes, the results clearly showed just how much good the Caribbean king crabs were doing. While the coral reef sections that scientists didn’t touch saw no change in their seaweed coverage, the sections that were stocked with crab saw seaweed coverage drop to nearly 50%, while the sections divers scrubbed first dropped by nearly 80%.

These results were so definitive and startling that researchers insisted on replicating the experiment in a different location to ensure they were onto something — a second experiment that yielded virtually the exact same outcome.

Researchers note, however, that while Thursday’s study shows just how effective crabs can be at repairing coral reefs, sweeping conservation efforts are still desperately needed. The study reports that establishing new coral reef nurseries to raise Caribbean king crabs is going to be a crucial step moving forward, one that researchers are currently pursuing.

Butler says that the study will only reach its true potential if it is used in conjunction with meaningful conservation efforts and a willingness to solve these complex problems threatening Earth’s underwater wonders.

“Conquering the challenge of climate change coupled with local reef restoration, like development of stocking programs for herbivorous crabs, are immediately necessary to reverse this decline,” Butler said. “Our findings mean little if they don’t result in tangible new restoration efforts.”

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