1. Larval culture of coconut crabs

 In order to restore the coconut crab population at Green Island, we reared larvae of B. latro in the laboratory to the zoeal stage. Crabs generally spawn in the dusk at high tide coinciding with a dark phase of the moon in summer. Female crabs carrying dark-brown mature eggs were collected when they walked down to the edge of the sea to wash their eggs. The mature eggs immediately hatch to 1st zoeae when eggs contact the seawater.

 Zoeae were kept in filtered seawater at a temperature 24~25 °C and a salinity of 34~35. In general, larvae have five zoeal stages which last 29 to 31 days (Reese, 1968), but in 2003, of a total of 13 glaucothoes which were reared from 300 zoeae, among them about 50% of those glaucothoes emerged from larvae which shortened their zoeal stages from 3rd zoeae to glaucothoes on the 25th~28th days. Morphologically, the thoracic appendages of those skip-developed individuals at the 3rd zoeal stage looked like those of 5th zoeae, and the telson was armed with 8 + 1 + 8 processes similar to those which molted to 4th zoeae. Those skip-developed individuals had a significant shorter larval duration than those which emerged from 5th zoeae. Since the coconut crab has the shortest larval stages among the Coenobitidae, comprising land hermit crabs, we suspect that this skipped development has positive adaptive significance for terrestrial living. Some glaucothoes began amphibious life on the 32th day of life in the laboratory. They swam by using the pleopods, crawled along the bottom, and emigrated from the sea water to the land. In 2003, all glaucothoes did not carry a gastropod shell and died soon (Chen & Wang, 2004).

 The results of studying in 2004 showed that when fed Artemia nauplii enriched with polyunsaturated fatty acids, (n-3) HUFAs, EPA, DHA, etc., the survivorship of zoeae significantly increased. In total, 20 glaucothoes emerged from 5th zoeae (no skipped situation was detected), and 6 glaucothoes carried the gastropod shell in their amphibious life (Fig. 1). These preliminary but promising results indicate that the artificial seeding of juveniles is workable. So a technique of mass culture of juveniles is now being developed.

Fig. 1 A glaucothoe of Birgus latro hiding in a gastropod shell. This individual metamorphosed to a glaucothoe from 5th zoeal stage on the 27th day and began carrying the shell on the 37th day of its life.

2. Investigation of Juvenile Habitat

 We investigated the distribution of juvenile coconut crabs in Green Island in 2003 and 2004. Four juvenile coconut crabs without carrying shell were found in coastal shrubs and farmland which were away from shoreline 500m after sampling 6 sites where a total of 52 adults were encountered in 2 years (Fig. 2). The cephalothoracic length of juvenile crabs were about 19~23 mm. The results of low recruitments reinforced the necessity of replenishing natural population by artificial cultivation and preserving habitat diversity.

Fig. 2 A juvenile crab of Birgus latro. It was found in farmland in 2003.

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