In recent decades, coral reefs worldwide have faced severe threats, resulting in the loss of half of the world’s corals and a staggering 90 percent decline in Florida’s coral populations. The situation escalated this summer when a devastating heatwave hit the Caribbean, pushing Florida’s coral reefs, particularly the largest continental US reef in the Florida Keys, closer to the brink of collapse.
This article is part of Xeeis’s series on the coral bleaching crisis in Florida, supported by a grant from the Pulitzer Center. Be sure to read the other stories in this series.
The decline of coral reefs is not only an ecological catastrophe but also poses significant challenges to wildlife and coastal communities. Coral reefs serve as vital habitats for up to 25 percent of marine species, including commercially important fish, and act as natural barriers protecting coastal areas from the impact of severe storms. In essence, the preservation of coral reefs is imperative.
But here’s where crabs come into play.
Scientists are currently working on assembling a formidable crab army, consisting of hundreds of thousands of crustaceans, to deploy on Florida’s reefs. This ambitious initiative aims to provide a lifeline to these ailing ecosystems.
Crabs as Coral Allies The Mote Marine Laboratory and Aquarium on Summerland Key in the Florida Keys houses a unique laboratory dedicated to these crustacean soldiers. Jason Spadaro, a marine ecologist and a devoted crab enthusiast, leads this groundbreaking effort. His mission is to breed a quarter of a million Caribbean king crabs annually, not for seafood consumption (although these crabs are delectable), but to assist the struggling coral reefs.
The crabs’ significance lies in their diet. Caribbean king crabs are prodigious consumers of seaweed, also known as macroalgae. Algae overgrowth has become a severe problem for reefs worldwide, particularly in Florida, hindering their growth and recovery from events such as marine heatwaves.
Algae thrives on nutrient-rich pollution that flows into the ocean, primarily from sewage and agricultural runoff. As pollution levels rise, so does the proliferation of algae.
Simultaneously, the populations of algae-eating animals have dramatically declined. Longspined sea urchins, which once played a crucial role in maintaining algae levels, were decimated by an unknown pathogen in the 1980s. Overfishing and ecosystem loss have also contributed to the decline of algae-eating fish like parrotfish.
In this scenario, algae thrives unchecked. Over the past decade, global reef algae coverage has increased by about 20 percent, transforming vibrant, colorful reefs into monotonous green patches.
This rampant algae growth is detrimental to coral reefs. Thick layers of seaweed make it challenging for baby corals, which begin as oceanic larvae, to find suitable seafloor locations to establish colonies. The algae not only occupies space but also limits sunlight penetration (critical for coral growth) and releases chemicals that deter coral settlement. Moreover, excessive algae competes with mature coral colonies for space, further exacerbating the problem.
Caribbean king crabs have emerged as voracious algae consumers, surpassing most other fish and invertebrates in the Caribbean. In a 2021 study led by Spadaro, reefs stocked with Caribbean king crabs exhibited an 85 percent reduction in algae cover compared to untreated reefs after just one year. This reduction in algae levels appeared to benefit the coral, leading to a higher density of young corals and an increase in fish species associated with coral reefs.
These findings highlight the crucial role of Caribbean king crabs as allies in the fight to save coral reefs.
Additionally, Caribbean king crabs are native to Florida, albeit in limited numbers, as they are preyed upon by various species. Therefore, introducing them to the reefs is unlikely to result in unintended ecological consequences, especially considering the scarcity of other herbivores.
Training Crabs for the Task While Spadaro currently oversees approximately a hundred crabs in the Florida Keys and nearly 200 more at a new breeding facility in Sarasota, the release of these crabs into the ocean is scheduled to commence by the end of this year or early 2024.
Before these lab-raised crabs can be reintroduced to their natural habitat, they need to learn to recognize and avoid predators since they have no prior exposure to them. One innovative method to achieve this is through the use of hand puppets.
Because the crabs’ vision is limited, Spadaro and his team employ predator-modeled hand puppets. By placing these puppets in the tanks and simulating predatory movements near the crabs, the crustaceans learn to perceive the threat and move away from it. This approach may seem unconventional, but it is an essential step in ensuring the crabs’ successful integration into their natural ecosystem.