Protection of land crabs critical to the conservation of coastal tropical forests
Morgan Erickson-Davis & Jeremy Hance
July 13, 2009
The impact of land crabs on the near-ocean forests in which they live has long been overlooked, with emphasis placed instead on water levels, salinity, and other abiotic influences. However, a new research synthesis published in Biological Reviews shows that land crab influence is among the most important factors affecting tropical forest growth along coasts, on islands, and in mangroves.
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. …
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). … “