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MEPS prepress abstract   -  DOI:

Population dynamics of the coconut crab Birgus latro on Aldabra Atoll, Seychelles

Jennifer Appoo*, E. Fernando Cagua, Janske van de Crommenacker, April J. Burt, Pierre Pistorius, Frances E. Taylor, Heather Richards, Philip Haupt, Naomi Doak, Frauke Fleischer-Dogley, Nancy Bunbury

*Corresponding author:

ABSTRACT: Birgus latro, the largest terrestrial arthropod in the world, has undergone a substantial decline globally over the last generations, with only a few healthy populations remaining where they are actively protected. We aimed to quantify demographic and spatio-temporal dynamics of a protected population of B. latro at Aldabra Atoll (Seychelles). Based on results along 2 transects on the atoll from 2007 to 2016, we calculated an average density of 23.7 ± 1.1 ind. ha-1 (mean ± SE). This suggests a population of around 5000 B. latro on Picard’s coastal area, which is likely to be an undercount due to the cryptic nature of the species. Numbers within the study area were stable over the study period and the population exhibited high spatial and temporal variability in count, size and sex ratio and in association with the lunar cycle. Aldabra’s B. latro population is male-biased (3:1 male:female), and is sexually dimorphic, with males being larger than females. Males and females moulted at different times of the year and the breeding season overlapped with the region’s wet season (December–March), and in synchrony with lunar phase. B. latro on Aldabra present colour polymorphism in a 4:1:1 ratio of orange:blue:intermediate (mixture of orange and blue). Results confirm that Aldabra is an important refuge for B. latro and potentially a natural source population for other areas in the region. Similar long-term studies on B. latro are encouraged to improve knowledge on the species and to support conservation actions to halt the species’ decline.