Survival and growth of juveniles of the coconut crab Birgus latro under laboratory conditions: implications for mass production of juveniles

Abstract

Populations of the coconut crab, Birgus latro (Linnaeus, 1767), have been depleted by primarily overharvest. The aim of this study was to develop artificial propagation technologies for the restocking and conservation of this species: it is a terrestrial hermit crab with aquatic larvae. Megalopae (post-larvae stage) were group cultured for six months with access to both “land” and “sea” areas (trial 1). In addition, shell-carrying juveniles aged one month were group cultured on land until the age of 13 or 24 months (trial 2). Furthermore, juveniles that had abandoned their gastropod shells were cultured individually and their moult and growth was monitored. The survival rates of animals ranged from 26-55% in trial 1, and they grew to a mean thoracic length (TL) of approx. 1 mm. In trial 2, the juveniles grew to a mean TL of approx. 4 mm at age 24 months. The juveniles changed their gastropod shells for larger ones according to their growth based on their body width. The juveniles found soon after abandoning their gastropod shells varied in size (2.5-8.6 mm TL), age (15-26 months old), and the degree of the formation of pleonal tergal plates. The juveniles without shells moulted 5-6 times during the culture period of 9-20 months. Two survivors grew to 6.8 mm TL and 11.9 mm TL at an age of 24 and 37 months, respectively. The body colour pattern of the juveniles was retained through successive moults. Our results demonstrated the feasibility of artificial production of the coconut crab juveniles and the utility of using natural marks to monitor their growth and migration after being released in the wild.