Protection of land crabs critical to the conservation of coastal tropical forests
Morgan Erickson-Davis & Jeremy HanceJuly 13, 2009
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Land crabs come in a variety of species from the tiny Ecuadorian Hermit Crab, which weighs less than an ounce, to the Coconut Crab which, at 38lbs, is the world's largest terrestrial invertebrate. While many species are similar in appearance to their aquatic relatives, land crabs exhibit an array of unique adaptations, the most notable and universal being an inflatable organ covering their gills which acts as a lung. In addition to an ability to extract oxygen from the air, many species of land crabs can extract moisture from their surroundings (from the soil they burrow into or the food they eat, for example), necessitating their return to the sea only to reproduce.
 Harlequin Land Crab in Corcovado National Park, in Costa Rica. Photo by Erin Lindquist |
However, recent research has begun to reveal the true nature of the crabs' impact on their environment.
"Because their predation on seeds and seedlings has been found to be selective in some studies (preferring some plant species over others), land crabs may promote the growth and establishment of rare species of plants which escape crab mortality," explains Dr. Lindquist. "In a tropical forest with many species of trees, competition for limited resources (light, water, soil nutrients, etc.) among tree species can limit recruitment (growth and survival). For example, crab predation may minimize the competition between a dominant (common) species and a rare species by reducing the number of seedling recruits of the dominant species. As a result the rare species is released from the competition and experiences higher survivorship (recruitment). Also, when a natural predator with such importance in the food web is removed from an ecosystem, the food web will deteriorate, and other members of the food web may become endangered or extinct. For example, if land crabs were removed from these coastal ecosystems, soil nutrient levels may decrease due to the decreased rates of litter decomposition (land crabs move leaf litter into their burrows thereby increasing litter decomposition and increasing nutrient return to the soil) which will in turn may limit plant growth."
 Harlequin Land Crab in Corcovado National Park, in Costa Rica. Photo by Rhett Butler |
In addition, land crabs are an important source of food for many other animal species in near-ocean tropical forests.
Dr. Lindquist recommends that in order to preserve tropical coastal forests, land crab populations must also be protected by encouraging the regeneration of disturbed forests, protecting those forests that are yet pristine, and implementing restrictions on the harvesting of land crabs.
"Given their large ecological role in forested coastal ecosystems, the conservation of land crab populations is critical to the conservation of the forest."
