Johngarthia lagostoma (H. Milne Edwards, 1837) on Ascension Island: a very isolated land crab population

Abstract

A study was made of the land crab, Johngarthia lagostoma (H. Milne Edwards, 1837) on Ascension Island in the central South Atlantic: aspects of its distribution, population structure, and reproduction are described. On Ascension it is normally limited to altitudes >200 m, the only parts of the island with substantial vegetation. The population comprised predominantly pale colour morphs, and few immature specimens were sampled. The significance of both factors is examined. The breeding migration to the shore was observed. Migrations occurred in February to April, varied in intensity between years, and were dominated by females. Migrants had to cross the bare arid lowlands, resulting in mortality. There are no recent records of the return of the juvenile crabs after the planktonic larval phase. Une etude a ete menee chez le crabe terrestre Johngarthia lagostoma (H. Milne Edwards, 1837) sur l'ile d'Ascension, dans l'Atlantique sud central : les aspects de sa repartition, la structure de sa population et sa reproduction ont ete decrites. Sur l'ile de l'Ascension, sa presence est limitee normalement aux altitudes >200 m, les seules parties de l'ile avec une vegetation substantielle. La population comprend des formes de couleur pâle et quelques specimens immatures ont ete echantillonnes. La signification de ces deux facteurs a ete examinee. La migration de reproduction vers la mer a ete observee. Les migrations ont lieu de fevrier a avril, varient en intensite suivant les annees, et sont dominees par les femelles. Les migrateurs ont a traverser les parties basses, denudees et arides, qui sont cause de mortalite. Il n'y a pas de donnees recentes sur le retour des crabes juveniles apres la phase larvaire planctonique.