Did you know that White Spotted Crabs have a preference for Triton Trumpet conchs? These shells are a rare find, especially large ones. Some scientists believe that the large Tritons might be one of the only natural predators of Crown of Thorn Starfish, which are increasing in our waters. (TIME on-line) While a shell collector may see it as an amazing find, that crab species has to compete with the other large crabs in its habitat for another shell.
Tampering with the shells can have an impact on the reproduction cycle and survivability of the species as well. Female egg production is influenced by the type and size of shell the crab inhabits. In addition, the larger the crab, the more eggs it can produce. (Iossi, et al., 2005) The crabs will seek out undamaged shells of the right size and proportion to help increase their odds of survival. Damaged shells increase the risk of succumbing to predation. (Bulinski, 2007)
Crabs locate shells by smelling the decay of dead mollusks.(Scully, 1986) The crab scavenges the shell and if no other crabs are around to compete for the shell, the crab will try it on for size and decide if it’s a good fit. Hermit crabs don’t just select any random shell. Imagine being a size 8 in shoes and forcing your foot into a 5. The size and shape of the crab also affects the types of shells they can inhabit. (Vance, 1972; Bulinski, 2007) White Spotted Crabs are highly selective and are generally found in the Triton’s Trumpets. (UH Manoa Bishops Museum) The availability of large shells is limited.
Hermit crabs don’t “take” shells because they think the shells are pretty. The shell is part of the crabs defense mechanisms and acts as a protective armor. Hermit crabs have soft abdomens and don’t produce hard calciferous exoskeletons like other crabs. (Bulinski)
Carmem L Iossi, Renata Biagi and Fernando L Mantelatto. (2005). Egg production and shell relationship of the hermit crab Pagurus brevidactylus (Anomura: Paguridae) from southern Brazil. Animal Biology (formerly Netherlands Journal of Zoology). Volume 55, Number 2 / July, 2005
Richard Vance. (1972). The Role of Shell Adequacy in Behavioral Interactions Involving Hermit Crabs. Ecology, Vol. 53, No. 6 (Nov., 1972), pp. 1075-1083
Erik Paul Scully. (1986). Shell Investigation Behavior of the Intertidal Hermit Crab Pagurus longicarpus Say. Journal of Crustacean Biology, Vol. 6, No. 4 (Nov., 1986), pp. 749-756
Katherine Bulinksi. (2007). Shell-selection behavior of the hermit crab Pagurus granosimanus in relation to isolation, competition, and predation. Journal of Shellfish Research. April 1, 2007