According to the article, the crabs have been bred in an environment without predators. Therefore they have to train the crabs how to protect themselves in order to survive in the coral reefs. Picture of using puppets to train crabs
I'm kinda surprised to see them training them one at a time. That's going to take ages. "OK, Roger has been successfully intimidated by the nightmare puppet. Looks like Brenda is next in line, someone bring in Brenda."
Making crabs even more appealing is that they’re native to Florida, just in relatively low numbers. (“Everything eats them,” Spadaro said.) Adding them to the reef is unlikely to have any grave unintended consequences for the ecosystem, Spadaro said, especially considering that there are few other herbivores.
According to the article, the crabs will help the coral by eating algae. Unfortunately, algae is great for (and sorely needed for) removing carbon dioxide from the air.
Also you're talking about microalgae, the stuff that makes water look green. The stuff the crabs would be eating is growing on the coral or is shading it like kelp.
Hopefully you are right! I just found it humorous that on one side of the world they’re growing algae to save the planet, and on the other side they are getting rid of algae to save the planet. 🤷♂️