Land Crabs as Nutrient Cyclers

Land crabs make burrows under trees (below)

Study by Elizabeth Luotto, Leo Lerner, & Brady Hartman

Nutrient cycling occurs in all environments and plays a key role in the composition of various habitats.  In Cabo Blanco, Costa Rica, nutrients move through multiple ecosystems from the ocean to the tropical dry forest to the atmosphere and back into plants and animals.  Land crabs burrow in this dry forest near the costal areas and contribute to the nutrient cycle in their local environment as soil engineers.  However, they are also known to prey on plant seeds and destroy seedlings affecting the success of plants in their immediate vicinity.  We investigated if the abundant tree species Adenocalymma inundatum nearby to these crab holes uptake more nutrients than those located further away.  To explore this question, we took samples of 30 individuals in the Cabo Blanco forest, both above and below the limestone bluff. Located about 150 meters away from the shoreline, the bluffs separate the forest into two different sections. We found that trees above the bluff had a higher nitrogen content when they were located close to crab burrows with a larger average diameter.  This same relationship was not present in trees below the bluff, or with other measures of crab burrow density such as the number of crab burrows, average distance to crab burrow, or nearest distance to crab burrow.  Soil moisture or canopy cover does not explain the difference in nitrogen content above the bluff.  Future studies should specifically investigate whether crab burrows above the bluff and the nutrient content within the soil near crab burrows are related in order to further explore the role of land crabs in nutrient cycling in the Cabo Blanco forest.

Brady Hartman taking measurements (L). Chlorophyll meter (top) and measuring nitrogen in leaf stems (bottom)