Some biological-population characteristics of mouthless land crab Cardisoma crassum (Crustacea: Gecarcinidae) in the mangroves of Tumbes, Peru

Abstract

Mouthless land crab Cardisoma crassum was studied in the mangrove ecosystem of Tumbes in order to locate and identify its main colonies, know the index of abundance (mean density and population), and some biological aspects and characteristics of its habitat. Twenty three biological stations were sampled in four zones that show a history record of the presence of C. crassum (SNLMT-ZA, Puerto Pizarro, Tumbes river-Cherrez, Corrales) by using the swept area method. The results show that individuals inhabit high areas of the mangrove ecosystem and in the mangrove-dry forest or mangrove-hypersaline lagoon transition section, along with the presence of vegetation type Avicennia germinans, Batis maritima, Prosopis chilensis, and Cryptocarpus pyriformis. The overall mean density was 0.7±0.5 ind.m², assessing an area of 340,915.9 m² and obtaining a population estimate of 250,744 individuals. The Tumbes River - Cherrez area presented the largest population size of C. crassum and the largest habitable area compared to the other zones (SNLMT - ZA, Puerto Pizarro and Corrales). Sex ratio was favorable to males (3.8 M: 1.0 H), registering only two ovigerous females. Mean size of cephalothorax width (CW) in female specimens was 75.6 mm, and 83.4 mm CW in males. There was a predominance of active burrows (open burrows with host) compared to inactive (closed burrows) and abandoned burrows. In addition, only male alometric specimens were observed.