Florida’s coral reef is in disaster. These crabs may help.

With large pincers and tough, spider-like legs, Caribbean king crabs don’t seem like your typical heroes. But these crustaceans could also be key to fixing one of many world’s most urgent environmental issues: the decline of coral reefs.

In latest a long time, warming seas, ailments, and different threats have worn out half of the world’s corals and 90 % of these in Florida. And this previous summer season, the issue accelerated. A devastating warmth wave struck the Caribbean, pushing the reef within the Florida Keys — the biggest within the continental US — nearer to the brink of collapse.

The decline of coral reefs is a gigantic drawback for wildlife and human communities. Reefs not solely present habitat for as a lot as 1 / 4 of all marine life, together with business fish, however additionally they assist safeguard coastal communities throughout extreme storms. Merely put, we want coral reefs.

Coral reefs, in the meantime, want crabs.

Fortunate for them, assistance is on the best way. Scientists are within the technique of constructing a crab military — tons of of hundreds of crustaceans sturdy — that they’ll unleash on Florida’s reefs, giving this ailing ecosystem a instrument to combat again.

Crabs to the rescue

Should you discover crustaceans icky, Jason Spadaro’s lab just isn’t a spot you wish to go to. Housed in a big, hurricane-proof constructing on Summerland Key within the Florida Keys, it’s filled with tanks which might be filled with crabs — dozens of them. Some are the scale of fingernails; others are as giant as dinner plates. All of them look a bit like rocks.

Spadaro, a crab fanatic and marine ecologist on the Mote Marine Laboratory and Aquarium, is heading up an bold plan: to breed 1 / 4 of 1,000,000 Caribbean king crabs annually. It’s not about cultivating seafood, although these crabs are certainly scrumptious, Spadaro stated. It’s about serving to coral reefs survive.

The secret is within the crabs’ diets: These critters eat huge portions of seaweed, also referred to as macro algae. Algae has been choking reefs all through the world and particularly in Florida, making it exhausting for them to develop and recuperate from damaging occasions like marine warmth waves.

Algae harms coral. Crabs eat algae.

Algae is without doubt one of the few winners in a world dominated by people. It thrives on our waste, corresponding to sewage and runoff from farmland, which is stuffed with nitrogen and phosphorous — vitamins that algae must develop.

As air pollution runs into the ocean, algae booms.

In the meantime, animals that eat algae have declined precipitously in latest a long time. Within the Eighties, an unknown pathogen worn out longspined sea urchins within the Caribbean. These marine invertebrates — which take the form of an overfilled pin cushion — eat a great deal of algae. Equally, overfishing and the lack of numerous ecosystems has prompted declines in algae-eating fish, corresponding to parrotfish.

Like a fertilized pasture with no cows, a discipline of algae on a reef with no herbivores grows unencumbered. Within the final decade, the extent of algae on reefs globally elevated by roughly 20 %, turning them from sensible fields of colour to monochrome patches of inexperienced.

It is a significant issue for coral.

When a thick layer of seaweed covers the reef, it’s exhausting for child corals — which spend their early days as larvae swimming within the ocean — to discover a spot on the seafloor and begin a colony. This seaweed not solely takes up flooring area however it could additionally restrict the quantity of daylight that reaches the underside (coral wants gentle to develop) and produce chemical compounds that dissuade corals from settling. Plentiful algae additionally competes with grownup colonies for area, crowding them out.

Throughout the Caribbean and in Florida, scientists are pouring their time and assets into restoring reefs by planting (or “outplanting”) bits of coral on the seafloor. But with out additionally ridding these ecosystems of algae, Spadaro stated, restoration could wrestle to succeed.

Enter: crabs.

Hungry crabs to the rescue

Caribbean king crabs are voracious algae eaters, consuming seaweed at charges “that exceed almost all different fish or invertebrate grazers within the Caribbean,” researchers wrote in a 2021 examine led by Spadaro.

For the examine, Spadaro in contrast typical reefs within the Florida Keys to these he had stocked with Caribbean king crabs at a density of about one animal per sq. meter. After a yr, the crab-filled reefs had about 85 % much less algae in comparison with reefs he left alone. A follow-up experiment discovered related outcomes.

“The impact of crab stocking on seaweed cowl was speedy and dramatic,” Spadaro and his co-author wrote. In flip, the lower in algae appeared to assist the coral. The reefs with crabs had a better density of younger corals, the examine discovered, and extra fish which might be usually related to coral reefs.

Outcomes like this point out that Caribbean king crabs are essential allies for coral reefs.

Making crabs much more interesting is that they’re native to Florida, simply in comparatively low numbers. (“The whole lot eats them,” Spadaro stated.) Including them to the reef is unlikely to have any grave unintended penalties for the ecosystem, Spadaro stated, particularly contemplating that there are few different herbivores.

Tips on how to practice a crustacean

Spadaro has roughly 100 crabs within the Florida Keys, and simply shy of 200 at a brand new breeding facility in Sarasota. He’ll begin dropping them into the ocean as quickly as the tip of the yr or in early 2024, he stated.

However there’s one step earlier than then, and it could contain … hand puppets?

As a result of the crabs are raised in a lab, they don’t have any expertise with predators. So earlier than placing them onto the reef, Spadaro and his workforce could should situation them to worry issues like octopuses, snappers, and groupers.

A method to do that is through the use of puppets modeled after predators. By placing these puppets within the tanks whereas poking on the crabs, the crabs study to maneuver away from the risk. A number of months in the past, Mote partnered with an area elementary faculty and had college students craft hand puppets, modeled after crab predators, to make use of in worry conditioning. (Happily, the crabs don’t have nice imaginative and prescient.)

Corals face numerous threats, together with ocean warming, that even the hungriest of crabs can’t repair, but crabs are an essential a part of efforts to revive ailing reefs. Scientists have, over a long time, discovered develop and plant corals to replenish reefs, Spadaro stated, however “now we have to assist them survive.”