Published August 31, 2003
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Shell condition and adequacy of three sympatric intertidal hermit crab populations
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TURRA, A. (2003): Shell condition and adequacy of three sympatric intertidal hermit crab populations. Journal of Natural History 37 (15): 1781-1795, DOI: 10.1080/00222930110116020, URL: http://www.tandfonline.com/doi/abs/10.1080/00222930110116020
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- urn:lsid:plazi.org:pub:FFE6FFB9FFA31D677B06FFB4FFD8525B
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- Although the three hermit crab populations used mainly undamaged shells, C. sclopetarius and C. vittatus occupied shells with epibionts more frequently than C. antillensis. According to Scully (1979) and Asakura (1995), the use of low-quality shells by hermit crabs occurs in sites with low shell availability. In fact, C. antillensis used shells of Cerithium atratum (Born, 1778), which were the most abundant in this area (Leite et al., 1998), while the two other species used low-availability shells ( Turra, 1998).
- The use of unbroken and highly encrusted shells may be associated with the regular dispersion pattern of C. sclopetarius and C. vittatus in the study area (Turra et al., 2000). Moreover, these two species mainly used shells of Chicoreus senegalensis (Gmelin, 1790) (Turra, 1998), the architecture of which is composed of strong spines, which according to Vermeij (1978) may reduce crab predation risks. This would be especially important given the high abundance of shell-crushing predators in the studied area, such as the blue crab Callinectes danae Smith, 1869. In addition, the use of highly encrusted shells may make the crabs cryptic (Partridge, 1980; Gherardi, 1990, 1991), thus also reducing the predation risks. The lower the predation risk, the more exposed (out of refuges) and dispersed the crabs can be. In contrast, the clumped dispersion pattern and the clustering behaviour of C. antillensis ( Turra et al., 2000) may be associated with the use of damaged and non-encrusted shells as argued by Gherardi (1991) for Clibanarius erythropus (Latreille, 1818) and by Turra and Leite (2000) for another population of C. antillensis at the Sao Sebastiao Channel. These authors suggested that the presence of damage and the absence of encrustation might expose these crabs to higher predation and desiccation risks. In this way, crabs in such shells are more frequently found in clusters than scattered, while scattered crabs more frequently use unbroken and encrusted shells (Gherardi, 1991; Turra and Leite, 2000).
- The high frequency of physical damage to the aperture of the shells used by the studied species may indicate, according to Bertness and Cunningham (1981), a high predation rate by shell-crushing crabs on gastropod and/or on hermit crab populations. Moreover, the presence of physical damage to the shells may enhance the predation risks on hermit crabs (Reese, 1969). In fact, hermit crabs avoid damaged shells (Conover, 1978; Taylor, 1981; Pechenik and Lewis, 2000). The crabs in the present study seldom used shells with holes. Perforations are extremely disadvantageous for intertidal hermit crabs, because they reduce the water-storing capacity of the shells, mainly when located in high spires ( Reese, 1969).
- The three co-existing hermit crabs in the studied area showed inter- and intraspecific shell partitioning regarding shell type and size (Turra, 1998). The degree of encrustation also differed among species as was shown for other hermit crab assemblages (Gherardi and Nardone, 1997). The variation in the degree of encrustation among reproductive classes was dependent on the crab species. Ovigerous females of C. sclopetarius and C. vittatus occupied proportionally less encrusted shells than males and non-ovigerous females. Similarly, males of C. antillensis used proportionally more encrusted shells than females. This may make males more cryptic when looking for mates and new shells outside refuges. Asakura (1995) showed that males used epibiota-covered shells more frequently and were more widely dispersed than females of Diogenes nitidimanus (Terao, 1913). On the other hand, Gherardi (1990) showed that the degree of encrustation did not vary between males and females of Calcinus ornatus (Roux, 1830) and Clibanarius erythropus (Latreille, 1818). The degree of breakage did not differ among sexes for the three studied populations, or for the populations studied by Gherardi (1990) and Asakura (1995). In fact, both sexes appeared to avoid the risks imposed by the use of broken shells.