Living Sanibel: Mangrove Tree Crab important food source for many species
The mangrove crab is an important food source for several specialized species of birds, as well as a number of fish species that frequent the labyrinth-like root systems of the red mangrove during periods of high tide. Both the black and yellow-crowned night herons feed extensively on the mangrove tree crab, earning these birds the nickname “crab-eaters.” From the water, both the redfish and the mangrove snapper are partial to the mangrove tree crab, which they sometimes snatch off of low-hanging branches at high tide. It is also preyed upon by the much larger blue crab.
The mangrove tree crab is a vertical feeder, ascending into the red mangrove canopy during high tide then descending into the roots and exposed mud flats during low tide. It shares this mangrove environment with the similar-looking mangrove root crab (Goniopsis cruentata). Distinguishing one from the other is problematic in the field, but the primary difference is that the root crab has distinctive reddish-colored legs and lacks the spots generally present on the mangrove tree crab.
The mangrove tree crab lays between 5,000 and 35,000 eggs after mating. Less than 1 percent survives into adulthood. Most of the predation occurs during the larval stage of the crab’s life when the animal is small enough to be considered zooplankton. This tiny creature is eaten by barnacles, oysters, minnows, and filter feeders as they drift through the water column.
Although the mangrove tree crab population experienced a decline after the hurricane seasons of 2004 and 2005, it appears to be rebounding on the islands. One of the best locations to spot one is the red mangrove overlook located just before mile marker one on Wildlife Drive. It takes some time to spot this small crab because it disappears into the bark patterns found on the red and black mangrove and seldom moves. The best method is to scour a single tree and its roots. It takes a while, but on average you can find 30-50 of them between the road and the end of the overlook.
This is an excerpt from The Living Gulf Coast – A Nature Guide to Southwest Florida by Charles Sobczak. The book is available at all the Island bookstores, Baileys, Jerry’s and your favorite online sites.