This year Dr. Marc Albrecht with UNK Distance Master’s students Ms. Amanda Ford and Senior Master Sergeant Russell Forsee (Air Force), with funding from the U.S. Fish and Wildlife Service undertook a study of the giant blue land crab (Cardiosoma guanhumi) on Vieques. Other UNK Master’s students how worked on this project were Courtney Hemmert, Kathryn Hoffman, and Sharon Hyak. Also contributing greatly to this effort were L. Quiñones, los dos Pedros, and a number of members of the non-profit turtle conservation group Tictove: S. Burgos, A. Cruz, J. Fernandez, L. Martinez, F. Peterson, J. Ramos, M. Rodriguez.
This project had two main parts. The first was to find and if possible quantify the larval land crab. The eggs of this species are released into brackish or seawater by females. The larvae quickly hatch and begin an approximately 30 day cycle of maturation and growth during which they transform from zooplankton to tiny crabs and come crawling back out of the water to land. This part of the project had good success, larvae were found at a number of locations. The data are still being analyzed.
The second part of the project was to permanently mark crabs in a way their population can be calculated and followed into the future. These crabs are taken for food by people on Vieques, either for their own consumption or sale to restaurants on Puerto Rico (where populations of these crabs have been depleted due to hunting). This part of the project involved working at night in crab areas, typically near mud flats behind bays on Vieques. This was hard work for the crew, often working after a full day at a regular job, then grabbing dinner, and then meeting Mr. Forsee and heading back out until 11:00 pm at night! But the rewards were great. In just over a week nearly 400 crabs were captured, weighted, measured, tagged and released.
The giant blue land crab is a fascinating animal. They can live for over 10 years, up to how old is not known. They can get very large. Our work found crabs over 800 grams. These animals dig branching burrows that can penetrate 3 m or more into the ground. It is not clear if individuals occupy particular burrows for one year or many. During mating season they often leave the burrow areas, moving kilometers inland scaling trees and fences in their way. Reportedly juveniles live near or inside burrows of adults that presumably are not related to the young in any way. The burrowing and eating activities of these animals add to the nutrient cycling of the mangrove and costal ecosystem. They probably represent a large proportion of the terrestrial animal biomass of the ecosystem in which they occur.
Other projects are ongoing as part of this work. Ms. Hyak examined burrow density, distance from water, and burrow size distribution. Mr. Forsee is also monitoring a group of captive crabs to determine their tolerance to the tags used, and trying to encourage molting in captivity.