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

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

In current 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 most important within the continental US — nearer to the brink of collapse.

The decline of coral reefs is a gigantic downside 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 in addition they assist safeguard coastal communities throughout extreme storms. Simply put, we want coral reefs.

Coral reefs, in the meantime, want crabs.

Lucky for them, assistance is on the way in which. Scientists are within the means of constructing a crab military — lots of of hundreds of crustaceans robust — that they’ll unleash on Florida’s reefs, giving this ailing ecosystem a software to battle again.

Crabs to the rescue

If you discover crustaceans icky, Jason Spadaro’s lab will not be a spot you need to go to. Housed in a big, hurricane-proof constructing on Summerland Key within the Florida Keys, it’s filled with tanks which can be filled with crabs — dozens of them. Some are the scale of fingernails; others are as massive as dinner plates. They all 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 one million 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 monumental portions of seaweed, also called macro algae. Algae has been choking reefs all through the world and particularly in Florida, making it laborious for them to develop and get better 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, similar to sewage and runoff from farmland, which is stuffed with nitrogen and phosphorous — vitamins that algae have to develop.

As air pollution runs into the ocean, algae booms.

Meanwhile, animals that eat algae have declined precipitously in current a long time. In the Nineteen 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. Similarly, overfishing and the lack of varied ecosystems has brought on declines in algae-eating fish, similar to parrotfish.

Like a fertilized pasture with no cows, a subject of algae on a reef with no herbivores grows unencumbered. In 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.

This is a major problem for coral.

When a thick layer of seaweed covers the reef, it’s laborious 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 ground house however it may well additionally restrict the quantity of daylight that reaches the underside (coral wants gentle to develop) and produce chemical substances that dissuade corals from settling. Abundant algae additionally competes with grownup colonies for house, crowding them out.

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

Enter: crabs.

Hungry crabs to the rescue

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

For the research, 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 12 months, the crab-filled reefs had about 85 % much less algae in comparison with reefs he left alone. A follow-up experiment discovered comparable outcomes.

“The effect of crab stocking on seaweed cover was rapid and dramatic,” Spadaro and his co-author wrote. In flip, the lower in algae appeared to assist the coral. The reefs with crabs had the next density of younger corals, the research discovered, and extra fish which can be sometimes related to coral reefs.

Results 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. (“Everything eats them,” Spadaro stated.) Adding 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.

How to coach 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 12 months or in early 2024, he stated.

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

Because 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 crew might should situation them to worry issues like octopuses, snappers, and groupers.

One manner to do that is by utilizing 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. Several months in the past, Mote partnered with a neighborhood elementary faculty and had college students craft hand puppets, modeled after crab predators, to make use of in worry conditioning. (Fortunately, 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, found out learn how to develop and plant corals to replenish reefs, Spadaro stated, however “now we need to help them survive.”