ABSTRACT: Intertidal-zone hermit crab populations in the Quirimba Archipelago occur in high densities and many species overlap considerably in terms of spatial distribution and types of shell used. The suites of shells used by 5 mid- to supra-littoral hermit crab species were studied (using multivariate analyses) across 3 shore zones, 7 islands and several levels of mollusc fishing pressure. Potentially high intra- and inter-specific competition for resources in the Quirimba Archipelago hermit crab assemblages is alleviated by a degree of macrohabitat and shore zone separation but largely by significant partitioning of shell resources. The suite of shells used by each species was distinct, even if certain types were in common. The highest influence on shell usage was tidal height followed by shore-zone area and hermit crab identity. Where the spatial distributions are tighter (in the supra-littoral), the resource (shell) partitioning is greater. Fishing pressure (and associated abundance of target-species shells) was generally unimportant, but 1 species, Coenobita cavipes, used harvested shells opportunistically in proportion to their availability. Shannon H' and species-richness values of shells used increased with shore zone area in the upper shore zone but not in the supra-littoral zone. It is suggested that this was due to high fishing pressure on certain mollusc species making certain shells abundant for hermit crabs (shell middens were deposited on the supra-littoral zone). The results suggest a tight niche mosaic of the many hermit crab species in the Quirimba Archipelago.

KEY WORDS: Hermit crab · Niche width · Shell use · Resource partitioning

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Published in MEPS Vol. 206 (2000) on November 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000