Little-studied species of tiny crabs are at risk of extinction, researchers say, as coral reefs continue to disappear.

A new study by researchers from the University of Florida highlights the increasingly vulnerability of cryptochirid crabs, sometimes called gall crabs or coral gall crabs. There 52 known species of the minuscule crustaceans, some as small as a pea.

And as the new paper reveals, their tiny size is closely tied to their preferred coral environs. In tracing the body size of 792 species of prehistoric crabs and lobsters, post-doctoral researcher Adiel Klompmaker found habitat -- particularly coral -- has a predominant influence on the evolution of body size.

As animal lineages diversify, body sizes increase, as a general rule. But while the same trends can be seen among crustacean lineages, researchers found minimum body sizes (the lower end of the evolutionary range) remained the same over time.

Researchers say that's because gall crabs evolved smaller body sizes as they diversified across new reef environs during the Mesozoic Era. The crabs' small sizes allow various species to slip into the cracks of intimate coral environs.

Together, these crabs and their coral homes have evolved a harmonious relationship. The coral crevices offer the crabs a place to hide and hunt, and the crabs can ward off small coral-eaters.

But in the Caribbean and elsewhere, coral reefs (and the tiny crabs that call them home) are struggling from threats of pollution, rising ocean temperatures and ocean acidification.

"The addition of human influences pushes some of these reefs over the edge," Klompmaker said in a press release. "Many species of crab are so strongly adapted to reef life, they simply won't survive elsewhere, including 52 species of tiny cryptochirid crabs that live inside corals all over the world, including in Florida."

Unless more is done to protect coral, Klompmaker says unique species like cryptochirid crabs will soon be gone.