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Marine Ecology Progress Series

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MEPS 665:103-113 (2021)  -  DOI:

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

Jennifer C. Appoo1,*,#, E. Fernando Cagua1,2,#, Janske van de Crommenacker1, April J. Burt1,3, Pierre Pistorius1,4, Frances E. Taylor1,5, Heather Richards1,6, Philip Haupt1,7, Naomi Doak1, Frauke Fleischer-Dogley1, Nancy Bunbury1,8

1Seychelles Islands Foundation, Victoria, Mahé, Seychelles
2Center for Integrative Ecology, School of Biological Sciences, University of Canterbury, Christchurch 8041, New Zealand
3Department of Plant Sciences, Oxford University, Oxford OX1 3RB, UK
4Department of Zoology and Institute for Coastal and Marine Research, Nelson Mandela University, Port Elizabeth 6031, South Africa
5SoftFrog cc, Port Elizabeth 6070, South Africa
6Royal Society for the Protection of Birds, South East England Regional Office, Brighton BN1 1UF, UK
7Ichthyology Department, Rhodes University, Grahamstown 6139, South Africa
8Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn TR10 9FE, UK
*Corresponding author:
#These authors contributed equally to the work

ABSTRACT: Birgus latro, the largest terrestrial arthropod in the world, has undergone a substantial decline globally over the last decades, 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 on Aldabra Atoll (Seychelles). Based on results along 2 transects on the atoll from 2007 to 2016, we calculated an average (±SE) density of 23.7 ± 1.1 ind. ha-1. This suggests a population of around 5000 B. latro in the coastal area of Picard Island, which is likely to be an underestimate due to the cryptic nature of the species. The average density within the study area was stable over the study period, and over the yearly cycle, 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 sexually dimorphic, with males being larger than females. Males and females moult at different times of the year, and the breeding season overlaps with the region’s wet season (December-March) and was in synchrony with the 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.

KEY WORDS: Arthropod conservation · Population size · Spatio-temporal variability · Seasonal dynamics · Moulting · Reproductive season · Indian Ocean

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Cite this article as: Appoo JC, Cagua EF, van de Crommenacker J, Burt AJ and others (2021) Population dynamics of the coconut crab Birgus latro on Aldabra Atoll, Seychelles. Mar Ecol Prog Ser 665:103-113.

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