Marine Invertebrates of Bermuda Verrilli's Hermit Crab Calcinus verrilli By Heather Schongar and James B. Wood and Kim Zeeh - Editors Abstract  Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract


Hermit crabs are the only crabs without a complete exoskeleton and hide their soft, vulnerable abdomens in gastropod shells. The fit of the shell affects growth, survival and fecundity of the hermit crab (Hahn et al., 1998). Calcinus verrilli is the only endemic hermit crab in Bermuda, discovered in 1901 by Addison Verrilli (Sterrer, 1992). It is mainly found in intertidal regions. (Markham, 1977). C. verrilli has been fround to not only occupy loose gastropod shells but also sessile vermetid tubes (Rodrigues, 2000). Three precopulatory behaviors between the males and females are preformed before the nine second copulation. (Hazlett, 1973). Detrimental associations between sea anemones and algae on the outside of the hermit crab shells will cause the shell to become weak and eventually uninhabitable. (Rodrigues, 2000). C. verrilli will either be scavengers or filter feeders depending on their shell preferences (Markham, 1977). Shell ! rot may also affect C. verrilli, and may even cause fatality (Vogan et al., 2002). Recent research of C. verrilli has been done on the pressures of shell selections. (Hahn et al., 1998, Garcia et al., 2001, Gherardi et al., 2005 and Angel, 2000). C. verrilli also displays some sexual dimorphism when choosing shell preference, although the reasons for this are relatively not understood (Rodrigues et al., 2000 and Gherardi, 2004). Most marine hermit crabs do not have any commercial importance. There are no Bermudian laws governing C. verrilli.

Taxonomy


Phylum: Arthropoda
  Class: Crustacea
    Order: Decapoda
      Family: Diogenidae


Habitat


Calcinus verrilli is the only hermit crab that is endemic (only found in one area) to Bermuda (Sterrer, 1986). It is found in five main marine areas: intertidal, subtidal, “boilers”, patch reefs and rim reefs (Rodrigues et al., 2000). C. verrilli was found to be particularly abundant at damaged reef and grounding sites. The reason for the increased abundance is thought to be due to the fact that there are fewer coral colonies for protection of fish, so hermit crabs have taken over as the dominant herbivores on these damaged reefs. (Rodrigues, 2000). The complete depth range of C. verrilli is still unknown, although crabs have been collected at depths of 110 meters (Markham, 1977).

Since C. verrilli is mostly found in the intertidal and subtidal zones where it is constantly being hit with strong currents and waves that cause the crab to struggle against the surge. Due to the strong water movements and competition for gastropod shells, some C. verrilli choose to occupy shells of Spiroglyphus irregularis (a vermetid found in Bermuda) (Rodrigues, 2000). These shells are permantely attached to rocky areas so the hermit crabs movement is severely limited, although these shells will provide high protection from strong water currents and predators. C. verrilli are the only hermit crabs in Bermuda that have adapted this behavior of shell selection and more females than males occupy the vermetid shells (Markham, 1977).

Ecology


In the early 1900s a zoologist from Yale University, Addison Verrilli, discovered a new type of hermit crab on the Bermudian reefs (Sterrer, 1992). At first this crab was thought to be in the genus Clibanarius but in 1908 Verrilli recognized the crab as a Bermudian endemic species and reclassified it in the genus Calcinus (Rodrigues, 2000). C. verrilli is a small hermit with a purple and red spotted body. Like all hermits in the Calcinus genera they have well calcified carapaces, long and slender eyestalks, and the surfaces of the first three periopods (walking legs) are hairless and spineless (Wooster, 1984). Also, as with all Malacostraca hermit crabs, they have a thorax with eight segments, six to seven abdominal segments and flattened uropods that form the tail (Pechenik, 2000). Hermit crabs have a soft, vulnerable abdomen where a thin exoskeleton is present. Because of this extreme vulnerability they inhabit gastropod shells that serve as a protective covering (Hahn et al., 1998). The particular fit of this mobile home has a direct effect on a hermit crabs growth, survival and fecundity (Angel et al., 2000). Damaged or ill-fitting shells have a detrimental effect on the mating and feeding behaviors and are considered to be the limiting resource which restricts populations (Rodrigues et al., 2000). The soft abdomen is asymmetrically coiled to fit inside the shell/columnella and the hermit crab holds on with its uropods that act like hooks (Rodrigues, 2000).

The breeding season of C. verrilli begins in the middle of May and extends through late August. At the start of mating, three distinct precopulatory behaviors are preformed. The male begins the courtship by a tapping on the female’s chelipeds (claws) and legs with his own chelipeds. While the tapping is occurring, the male draws the female towards him by regressing into his shell and pulling her with his legs. Finally, just before copulation, the female palpates the male’s mouthparts with her chelipeds and legs. The copulation is nine seconds long and the female carries the eggs on her pleopods (swimmerets) until they are ready to develop (Hazlett, 1973). The larvae will swim around as plankton for a few weeks before settling to the reef floor (Pechenik, 2000).

Shell competition is a limiting factor for C. verilli, so that fighting between the hermit crabs for shells is a common occurrence. Typically the attacking crab will bring its shell down on the attacked crab’s shell. C. verilli has slower, weaker raps than other Calcinus species although there is strategic positioning of the attack (Hazlett, 1973). Usually the attacker will examine the external characteristics of the defender’s shell, and may even examine the inside with the chelipeds. The attacker will then rap several times on the defenders shell and might try to knock it over. The defender is either pulled out or comes out of its shell willingly. The attacker will then move into the defenders shell and may stay inside or move back into its old shell. After the attacker has made a shell selection the ‘naked’ defender will move into the remaining shell (Rodrigues, 2000).

Sometimes there are detrimental associations between the growth of organisms on the shells of C. verrilli and other hermit crabs. Algae and sea anemones can grow on the outside of the hermits shell, eventually making it more fragile and possibly unlivable. Although these organisms may provide predator protection, the degradation of the shell outweighs the benefits (Rodrigues, 2000). Other organisms such as Nereid worms, polychaetes, copepods, and porcellanid crabs will co-habitate with the hermit crabs inside the shell. These associations are also detrimental because less space is available to the crab and shell damage may occur (Rodrigues, 2000).

Most hermit crabs are scavengers and detrital feeders, sifting sediment to find food and snipping algae from the reef bottom. However, the hermits that occupy vermetid tubes are sessile and must turn to filter feeding as their feeding strategy. C. verrilli that live in vermetid tubes will generate a current with its antenna and removes particles from them as they become trapped (Markham, 1977).

Although crustaceans inhabit the ocean, disease is still a prevalent problem. One of the main problems affecting hermit crabs, as well as all other crustaceans is shell disease, also known as shell rot. Since chitin is abundant in marine environments as an important nutrient chitinolytic bacteria are common. The bacteria results in a breakdown of the chitinous exoskeleton of living crustaceans, leaving them with holes in their exoskeleton and vulnerable bodies. In the initial stages, shell rot is not fatal but if it continues it may result in unsuccessful shell molt and possible death by other bacteria that are able to gain entry through the shell holes. About ten percent of crustaceans get shell rot each year; although in unhealthy marine areas it may be a lot higher (Vogan et al., 2002)

Recent Research


Shell selection in hermit crabs is one of the most important choices that this organism can make. It is important in predation risk, growth, and fecundity. Most recent research on hermit crabs, as well as C. verrilli is being done on the selection pressures of shell preferences. Researchers have found that hermit crabs may be much attuned to the chemical cues of dead gastropods, which will direct them to available shells or warn them of possible predation in the area (Gherardi et al., 2005). Growth rate of hermit crabs is very dependant on the size and volume of not only the current shell, but also the size and volume of shells that are available. Smaller shells increase the risk of predation and increase the negative effects of the environment on hermit crabs (Garcia et al., 2001). Angel (2000) found that those hermit crabs that had smaller fitting shells had more activity than those with a better-fitting shell because of the probability of increased encounters with shells and the increased likelihood of finding an adequate shell. Some hermits show a severely decreased growth rate with shells that are too small for them. Sometimes, growth rates will reach zero or even become negative (Angel, 2000). Most hermit crabs prefer heavier fitting shells because of the intense wave action found in the intertidal areas they inhabit. It has also been found that hermit crabs will show a preference to previous shell types that they have inhabited. This serves to decrease the overlap of coexisting crab species and competition for shells (Garcia et al., 2001).

C. verrilli inhabits either gastropod shells or vermetid tubes. A sexual dimorphism is seen with shell selection with C. verrilli. The females are usually bigger than the males and prefer to live in the attached vermetid tubes, whereas the males prefer loose gastropod shells. It is relatively unknown why this difference in sexual shell preference occurs but a few theories have surfaced. Rodrigues et al. (2000) suggests that since females prefer the attached vermetid tubes, males do not need to be large to gain access to mating with females, while the bigger female size is beneficially with egg production. A second hypothesis makes note of the facts that gastropod shells allow for bigger body size and female egg numbers did not have a correlation with body size, which disputes the claims of Rodrigues et al. (2000). Gherardi (2004) hypothesizes that previous shell experience may also be a factor affecting the sexual dimorphism in shell preference of C. verrilli. Understanding the sexual dimorphism of shell selection is still not understood and further research needs to be done to understand these differences.

Commercial Importance


C. verrilli and few other marine hermit crabs have any commercial importance worldwide.

However, land hermit crabs, from the family Ctenocheildae, are commonly kept as pets by children and adults alike. Most land hermits are low maintenance, requiring only a clean cage with a sandy bottom, a few shells to choose from, food and water. Thousands of hermit crabs are sold every year and tons of websites and books have been written, directing the new owners how to keep their hermit crabs alive and happy. There is even a Hermit Crab Association that meets every year and has a convention and promotes proper care and treatment of hermit crabs (www.hermit-crabs.com).

Bermuda Laws


At the time this webpage was created, there are no Bermudian laws for C. verrilli, or any other hermit crab species. However, as with all Bermudican Marine Protected Areas, collection and disturbance are prohibited in these designated areas.

Personal Interest


My fascination with hermit crabs began when I purchased one as a pet as a child. Hermie the hermit crab was the beginning of my interest into marine organisms and ecosystems. At the beginning of this project I was pretty sure I knew almost all there was to know about the hermit crabs, but to my surprise I learned a lot from this project. After I read that C. verilli was the only endemic Bermudian hermit crab my interest piqued even more. Then, finding out about their unique lifestyles and how they have been able to adapt and change with the differences in reef types held my interest and all I wanted to do was find out more about how such a small organism could make a living in the big ocean.

Shell selection and pressures that influence it are very diverse and change throughout species, but hermit crabs may be more adaptive than we think. They may be able to control (to some extent) their growth rates depending on the shell size and availability. The adaptive and inquisitive nature of hermit crabs is truly amazing. Hermit crabs are the only crab species that has no entire exoskeleton, so their evolution of using gastropod shells as a ‘mobile home’ is not only necessary but extremely adaptive as well. Not only are hermit crabs cute, colorful and fun to watch, but they are also some of the most diverse and adaptive species of crustaceans.

References

Angel, J. 2000. Effects of shell fit on the biology of the hermit crab Pagurus longicarpus (Say). Journal of Experimental Marine Biology and Ecology. 243: 169-184.

Garcia, R. and Mantellato, F. 2001. Shell selection by the tropical hermit crab Calcinus tibicen (Herbst, 1791) (Anomura Diogenidae) from Southern Brazil. Journal of Experimental Marine Biology and Ecology. 265: 1-14.

Gherardi, F. and Atema, J. 2005. Effects of chemical context on shell investigation behavior in hermit crabs. Journal of Experimental Marine Biology and Ecology. 228: 35-51.

Gherardi, F. 2004. Resource partitioning between sexes in the “unconventional” hermit crab, Calcinus tubularis. Behavioral Ecology. 15: 742-747.

Hazlett, B. 1973. Shell fighting and sexual behavior in the hermit crab genera Paguristes and Calcinus, with comments on Pagurus. Bulletin of Marine Science. 22: 806-823.

Hahn, D. 1998. Hermit crab shell use patterns: response to previous shell experience and to water flow. Journal of Experimental Marine Biology and Ecology. 228: 35-51.

Hermit Crabs. www.hermit-crabs.com. Christa Wilkin - Editor

Markham, J. 1977. Preliminary note on the ecology of Calcinus verrilli, an endemic Bermuda hermit crab occupying attached vermetid shells. Journal of Zoology. 181: 131-136.

Pechenik, J. 2000. Biology of the Invertebrates, Fourth Edition. Boston: McGraw-Hill. pp. 578.

Rodrigues, L., Dunham, D., and Coates, K. 2000. Shelter preferences in the endemic Bermudian hermit crab, Calcinus verrilli (Rathbun, 1901). Crustaceana. 73: 737-750.

Rodrigues, L. 2000. Shelter use by Calcinus verrilli, Bermuda’s endemic hermit crab. Thesis: University of Toronto.

Sterrer, W. 1992. Bermuda’s Marine Life. Bermuda: Island Press. pp. 307.

Sterrer, W. 1986. Marine Fauna and Flora of Bermuda: A Systematic Guide to the Identification of Marine Organisms. New York: John Wiley and Sons. pp. 742.

Vogan, C., Costa-Ramos, C., Rowley, A. 2002. Shell disease syndrome in the edible crab, Cancer pagurus – isolation, characterization and pathogenicity of the chitinolytic bacteria. Microbiology. 148: 743-754.

Wooster, D. 1984. The genus Calcinus (Paguridae, Diogenidae) from the Mariana Islands including three new species. Micronesica. 18: 121-162.

Links

General Hermit Crab Information
Hermit Crab Symbiosis with Sea Anemones
Care for your Land Hermit Crab
The Hermit Crab Association