Shell utilization and morphometries of the hermit crab Diogenes brevirostris Stimpson

Abstract

Fecundity, shell utilization, and crab and associated shell morphometries were investigated for the hermit crab Diogenes brevirostris collected from three intertidal sites in the eastern Cape. The relationship between crab fresh mass and egg number was linear. D. brevirostris was found to occupy 33 gastropod shell species of which Bumupena predominated on the rocky shore (B. lagenaria, 35,9%; B. cincta, 17,5%; B. pubescens, 16,5%) while Bullia was more commonly used near sandy shores (S. armulata, 4%; B. digitalis, 2,7%; B. rhodostoma, 2,5%). Although Oxystele is common, it was hardly used by D. brevirostris (O. sinensis, 2,7%). Whereas shell type (Bumupena lagenaria, B. cincta, B. pubescens and Bullia rhodostoma) was found to have no significant influence on the crab length/mass relationships, significant differences were found between elevations but not slopes of the fresh mass/volume relationships (p < 0,05). B. rhodostoma was significantly different from all three species of Bumupena suggesting that small D. brevirostris occupy Bullia shells of a larger volume than a similar-sized crab occupying a Bumupena shell to compensate for the increased ‘dead space’ incurred with a high spire. Overall, there did not appear to be any selection towards low-spired (17 species, n = 264) or high-spired (15 species, n = 262) shell species, but there was when compared for each site (p < 0,01), indicating shell availability to be important. A good size correlation was found between 0. brevirostris and its associated shell suggesting that selection of available material and/or mutualism may occur.