Benji Jones works as a senior environmental correspondent for Vox, where he covers climate change and biodiversity loss. He worked as an Insider senior energy correspondent before coming to Vox. Prior to this, Benji was a wildlife researcher.
Caribbean king crabs aren’t your average heroes, with their enormous pincers and rough, spider-like legs. However, the loss of coral reefs is one of the most urgent environmental issues facing the planet, and tiny crustaceans might hold the key to reversing it.
Ninety percent of Florida’s corals and half of the world’s corals have perished in recent decades due to diseases, rising waters, and other challenges. And the issue got worse over the summer. The largest reef in the continental US, the Florida Keys reef, is getting closer to collapsing as a result of a disastrous heat wave that slammed into the Caribbean.
The loss of coral reefs poses a serious threat to both human societies and wildlife. Up to 25% of all marine species, including commercial fish, finds home on reefs, which also serve to protect coastal populations from strong storms. We really must have coral reefs.
Crabs are necessary for coral reefs, however.
Fortunately, assistance is on the way. Hundreds of thousands of crabs are being assembled by scientists to form an army that they plan to unleash on Florida’s reefs, providing this struggling environment with a means of defense.
Crabs coming to the rescue
Jason Spadaro’s lab is not a place you want to visit if you think crabs are gross. Located on Summerland Key in the Florida Keys, it is housed in a huge, hurricane-proof facility that is crammed with dozens of crab tanks. Some are as small as your fingernails, and some are the size of dinner plates. They all have a stone-like appearance.
Heading an ambitious effort to produce a quarter of a million Caribbean king crabs annually is Spadaro, a marine scientist at the Mote Marine Laboratory and Aquarium and an avid crab lover. It’s not about raising seafood, even though these crabs taste great, according to Spadaro. It’s about ensuring the survival of coral reefs.
The diets of the crabs hold the key: These creatures gobble up massive amounts of seaweed, or macro algae. Reefs all throughout the world, but particularly in Florida, have been choked by algae, which makes it difficult for the structures to develop and recover from harmful occurrences like marine heat waves.
Coral is harmed by algae. Algae is eaten by crabs
One of the few winners in a world where people rule is algae. It grows on human waste, including sewage and farm runoff, which is rich in phosphorus and nitrogen, two elements necessary for algae growth.
Algae blooms occur when pollution enters the water.
In the meantime, the number of algae-eating creatures has sharply decreased in recent years. Longspined sea urchins in the Caribbean were wiped out in the 1980s by an unidentified disease. These sea invertebrates consume a lot of algae and resemble an overstuffed pin cushion. Similar losses in algae-eating fish, including parrotfish, have been brought about by 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 past ten years, transforming them from vibrant swathes of color to monochromatic green patches.
This poses a significant risk to coral.
Baby corals, which spend their early days as larvae swimming in the ocean, find it difficult to find a site on the seafloor and form a colony when the reef is covered in a heavy covering of seaweed. This seaweed not only takes up floor space but also has the ability to create compounds that discourage corals from settling and reduce the amount of sunlight that reaches the bottom, which is necessary for coral growth. In addition, a profusion of algae pushes out adult colonies by competing for their space.
Scientists are dedicating a great deal of time and energy to rehabilitating reefs in Florida and the Caribbean by “outplanting” coral fragments on the seafloor. However, rehabilitation may not be successful if algae are not also removed from these habitats, according to Spadaro.
Now for the crabs.
Crabs that are hungry to the rescue
In a 2021 study headed by Spadaro, researchers noted that Caribbean king crabs consume seaweed at rates “that exceed nearly all other fish or invertebrate grazers in the Caribbean.”
For the study, Spadaro stocked Caribbean king crabs at a density of roughly one animal per square meter on normal Florida Keys reefs versus those he had not. Compared to the reefs he left alone, the crab-filled reefs had almost 85% less algae after a year. The results of a subsequent experiment were comparable.
Spadaro and his coauthor stated that “the effect of crab stocking on seaweed cover was rapid and dramatic.” The coral itself seems to benefit from the decrease in algae. The study discovered that there were more fish that are normally associated with coral reefs and a higher density of young corals on the reefs that contained crabs.
Findings such as these suggest that Caribbean king crabs are crucial allies of coral reefs.
The fact that crabs are endemic to Florida, albeit in very small quantities, adds to their allure. “Everything devours them,” stated Spadaro. Given the scarcity of other herbivores, adding them to the reef is not expected to have any serious unexpected effects on the ecosystem, according to Spadaro.
Teaching a Crustacean
About a hundred crabs are kept by Spadaro in the Florida Keys, and he has almost 200 at a new breeding facility in Sarasota. He stated that he will begin dumping them into the water in the beginning of 2024 or before the year ends.
However, there’s still one stage to go, and it might involve… hand puppets?
The crabs have never encountered a predator because they were grown in a lab. Thus, Spadaro and his crew might have to acclimate them to a fear of groupers, snappers, and octopuses before releasing them onto the reef.
Using puppets that are fashioned after predators is one approach to achieve this. The crabs are trained to avoid the threat by placing these puppets in the tanks and prodding them. In order to employ fear conditioning, Mote collaborated with a nearby elementary school a few months back and had the pupils make hand puppets that were fashioned after crab predators. (Thankfully, the crabs’ eyesight is poor.)
Even the most voracious of crabs cannot reverse the many problems that corals face, such as ocean warming, yet crabs play a crucial role in efforts to restore damaged reefs. According to Spadaro, scientists have spent decades learning how to cultivate and plant corals in order to restore reefs, but “now we need to help them survive.”