oa African Zoology - Patterns of distribution, abundance and shell utilization amongst hermit crabs, Diogenes brevirostris

Volume 22, Issue 4
  • ISSN : 1562-7020
  • E-ISSN: 2224-073X



Hermit crabs, Diogenes brevirostris, attained peak densities >600 m-2 in and around seagrass (Zostera capensis) beds on intertidal sand flats in Langebaan Lagoon. Hermits were found in 20 types of gastropod shell, and inhabited a predictable succession of shell species as they grew in hard carapace, or shield length. The availability of larger shells declined progressively, such that all suitable shells exceeding 6 mm in aperture width were occupied by hermits. Close relationships existed between crab size and both the type and aperture width of shell occupied, although utilization patterns in male and female hermits differed. In natural populations males dominated both the smallest and largest size classes, intermediate groups consisting almost exclusively of females. Numbers of eggs brooded by females increased as a power function of shield length, but varied little with shell species occupied. Laboratory populations given access to an excess of empty shells exchanged shells frequently and repeatedly, ending up in shells that were larger and often of different shape to those occupied in the field. All evidence suggests that growth, fecundity and population density in D. brevirostris are increasingly regulated by shell availability as growth proceeds.

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