If you’ve explored the vast Florida coastlines and any of the mangrove habitats in the Sunshine State, then you’ve been around mangrove tree crabs. This common and fascinating species can be found in tropical and subtropical parts of the America’s and has the scientific name Aratus pisonii. These small, dark crustaceans can be seen crawling atop mangrove trees during high tide and venturing onto the ground in low tide. Often, they are observed in large numbers traveling vertically up and around the branches.
Mangrove tree crabs have a grayish-brown, black or olive-green shell (carapace) and will average about 1-2 inches in size. The male crabs are typically slightly larger than females. Mangrove tree crabs are uniquely flatter in surface structure than other crabs and their legs are spread out to the side to better climb the trees in which they live. Unlike other crabs, their eyes are wideset on either side of their carapace. This likely aids their vision when navigating the mangroves.
Mangrove tree crabs are omnivores and feed mostly on detritus, algae, small invertebrates and animal matter. The most important part of their diet comes from the leaves of the mangrove trees in which they inhabit. Mangrove tree crabs reproduce year-round.
Even with their small size, the female can carry over 30,000 eggs on her back, depending on the width of her carapace. It is also believed that their hatching cycles coincide with moon phases, though the study is not conclusive.
Mangrove tree crabs are commonly preyed upon by shorebirds, fish and even other crabs that live in their mangrove environment. They use their quick speed, where they impressively can run up to a meter per second, as a defense mechanism to avoid predation.
While they are interesting to witness, these crabs also play an important role in the ecosystem by helping to break down plant and animal matter, and by providing food for other animals. Most importantly, by consuming the mangrove leaves, mangrove tree crabs help keep estuaries clean from leaf debris.
Mangrove tree crabs are fun to observe when visiting a coastal mangrove environment and, like so much of our wildlife, they play a crucial role in keeping Florida wild. Remember to keep our mangrove habitats clean and protect this local species so that we can enjoy the beauty of nature for years to come.