Coral reef – Courtesy: Shutterstock – Image by videotrinkets
With huge pincers and rough, spider-like legs, Caribbean king crabs don’t appear like your average heroes. Yet tiny crustaceans may be vital to alleviating one of the world’s most severe environmental problems: the collapse of coral reefs.
In recent decades, warmer waters, viruses, and other threats have wiped away half of the world’s corals and 90 percent of those in Florida. And the issue got worse this past summer. A severe heat wave slammed the Caribbean, pushing the reef in the Florida Keys – the largest in the continental US—closer to the edge of destruction.
The degradation of coral reefs is a significant challenge for animals and human societies. Reefs not only provide habitat for as much as a quarter of all marine life, including commercial fish, but they also help safeguard coastal populations during severe storms. Simply simply, we need coral reefs.
Coral ecosystems, meantime, need crabs.
Lucky for them, help is on the way. Scientists are in the process of developing a crab army — hundreds of thousands of crustaceans strong—that they’ll unleash on Florida’s reefs, giving this ailing environment a tool to fight back.
Crabs to the rescue
If you find crustaceans unpleasant, Jason Spadaro’s lab is not a place you want to visit. Housed in a big, hurricane-proof facility on Summerland Key in the Florida Keys, it’s full of tanks that are full of crabs—dozens of them. Some are the size of fingernails; others are as massive as dinner plates. They all resemble rocks a little bit.
The Mote Marine Laboratory and Aquarium’s Spadaro, a crab aficionado and marine ecologist, is in charge of an ambitious project to breed a quarter of a million Caribbean king crabs annually. Spadaro claimed that despite the fact that these crabs are wonderful, the goal is not to cultivate seafood. It aims to support the survival of coral reefs.
The crabs’ diets hold the key: The seaweed, also known as macroalgae, is consumed in vast quantities by these creatures. Reefs all throughout the world, but particularly in Florida, have been choked by algae, making it difficult for them to develop and recover from harmful events like marine heat waves.
Coral is hurt by algae. Alligators eat algae.
One of the few winners in a world ruled by people is algae. It feeds on human waste, including sewage and farming runoff, which are rich in the nutrients nitrogen and phosphorus that algae require to develop.
Algae bloom as pollution enters the ocean.
In the meantime, the number of animals that consume algae has sharply decreased recently. Long spined sea urchins in the Caribbean were exterminated by an unidentified infection in the 1980s. These aquatic invertebrates, which resemble overstuffed pin cushions, consume a lot of algae. Similar losses in algae-eating fish, like parrotfish, have been attributed to overfishing and the destruction of various ecosystems.
On a reef without herbivores, a field of algae blooms unhindered, much like a fertilized grassland without cows. Globally, the amount of algae on reefs has grown by about 20% in the last ten years, transforming them from vibrant fields of color to monotone patches of green.
Coral faces a significant issue because of this.
Baby corals, which spend their early stages as larvae swimming in the ocean, find it difficult to locate a location on the seafloor and establish a colony when a dense covering of seaweed covers the reef. This seaweed not only takes up space on the seafloor but also produces compounds that prevent corals from settling and can reduce the amount of sunlight that reaches the bottom, which is necessary for coral growth. Additionally, adult colonies are pushed away by abundant algae that compete with them for space.
Scientists are investing a lot of time and money into repairing reefs by “outplanting” pieces of coral on the seafloor throughout the Caribbean and in Florida. Spadaro cautioned that restoration efforts might be unsuccessful if these ecosystems are not also cleared of algae.
Crabs are here.
Rescued by hungry crabs
As voracious algae eaters, Caribbean king crabs consume seaweed at rates “that exceed nearly all other fish or invertebrate grazers in the Caribbean,” according to researchers in a 2021 study conducted by Spadaro.
Spadaro compared typical Florida Keys reefs to those that had been supplied with Caribbean king crabs at a density of roughly one animal per square meter for the study. When compared to reefs he left alone, the reefs with crabs had around 85 percent less algae after a year. A further trial produced similar outcomes.
“The effect of crab stocking on seaweed cover was rapid and dramatic,” wrote Spadaro and his co-author. In turn, it seemed that the coral benefited from the decline in algae. The study discovered that the reefs containing crabs had more of the usual coral reef fish and a higher density of new corals.
These findings suggest that Caribbean king crabs are crucial coral reef allies.
The fact that crabs are endemic to Florida, albeit in very small quantities, makes them even more alluring. “Everything eats them,” stated Spadaro. They won’t likely have any significant unintended effects on the environment, according to Spadaro, especially given the lack of other herbivores.
How to instruct a crab
Spadaro has just under 200 crabs at a new breeding facility in Sarasota and about 100 crabs in the Florida Keys. He promised to start dumping them into the ocean by the end of the year or the beginning of 2024.
However, there is a step that must be taken beforehand, and it might involve hand puppets.
The crabs have never seen predators because they were grown in a lab. Spadaro and his crew might need to accustom them to the dread of octopuses, snappers, and groupers before putting them on the reef.
Using puppets designed to seem like predators is one way to achieve this. The crabs are taught to flee the danger by having these puppets in the aquariums and prodding at them. A few months ago, Mote collaborated with a nearby elementary school to have children create hand puppets that were designed to look like crab predators and were then used for fear training. (Thankfully, the crabs can’t see very well.)
Even the most hungry crabs cannot stop the numerous problems that corals face, such as ocean warming, nevertheless, crabs play a crucial role in efforts to rehabilitate sick reefs. According to Spadaro, scientists have developed techniques over many years for growing and replanting corals to replenish reefs, but “now we need to help them survive.”
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Melissa’s career in writing started more than 20 years ago. Today, she lives in South Florida with her husband and two boys.
