Marine Invertebrates of Bermuda Purple Pincher Hermit Crab (Coenobita clypeatus) By Rebecca Karis with James B. Wood and Melissa Parr (Eds) Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract


Coenobita clypeatus is a terrestrial hermit crab found in tropical and sub-tropical areas. Living in humid areas this terrestrial hermit crab is a nocturnal scavenger that uses a gastropod shell to protect its soft body parts. These creatures are extremely social, foraging and traveling in groups. While C. clypeatus is extremely social the species is known to be aggressive towards other hermit crabs in their group to steal better fitting shells. C. clypeatus is also cannibalistic and will eat vulnerable molting crabs. While the purple pincher hermit crab is terrestrial it must return to the water to spawn and release it's larvae into the ocean.

In Bermuda the purple pincher hermit crab has an extremely small population. In 1994 their populations was estimated to be only 150 individuals. The current state of the C. clypeatus population pales in comparison to the population of the 1950s. The purple pincher hermit crab was said to be found every where on Bermuda, now it is only found in a single bay on the south shore. Recent research has pointed to shell availability as the determining factor in population size. Unfortunately there are no Bermudian laws protecting the dwindling C. clypeatus population.

Taxonomy


Phylum: Arthropoda
  Class: Crustacea
    Subclass: Malacostraca
      Order: Decapoda
        Family: Coenobitidae


Arthropods have an articulated, segmented, chininous exoskeleton (Wood 2007). Crustaceans have 5 paired head appendages, which include antennae, mandibles and two sets of maxilla. Crustaceans also have biramous appendages meaning they have two part appendages, each part performing a different function. Organisms in the class Malacostraca have trunks with fourteen segments, eight on the thoracic, six on the abdomen. Order Decopoda is defined by three thoratic appendages and five pairs of walking legs. Coenobita animals are named so for their communal living (Fenner 1999).

Habitat


Hermit crabs in the genus Ceonobita are found on tropical and subtropical islands in the Pacific, Atlantic and Indian Oceans (Chance and Hobbs 1969; Ball 1972; DeWiled 1973; Alexander 1979; Page and Willason 1982; Willason and Page 1983). Coenobita clypeatus is a tropical land hermit crab that lives throughout the Caribbean and as far north as Florida and Bermuda (Kurta 1982). C. clypeatus spends most of its time in the woods but is known to travel to high sand hills near the shore (Sterrer 1986). Because C. clypeatus has gills it must live in areas of high humidity. However their gills do not allow them to be fully submerged under water because the hermit crabs will drown. C. clypeatus has been found to travel across many different habitats and have climbed mountains as high as 887 meters (Walker 1994). In Bermuda these crabs once roamed all over the island but now they are only know to inhabit Hungry Bay a small bay on the south shore of the island (Hass 1950; Walker 1994).

Ecology


Activity
Coenobita clypeatus is a slow moving nocturnal terrestrial hermit crab (Hazlett 1964; Hazlett 1966). The crabs bury themselves beneath leaves, rocks, or sand during the day to avoid desiccation (Hazlett 1966). By being nocturnal C. clypeatus is temporally separated from its competitors (Morrison 2006).

The hermit crabs have a complex social structure. C. clypeatus uses “social facilitation as a foraging statagy” (Kurta 1982). This is an ordinary activity increased by the presence of others (Wilson 1975). The hermit crabs forage in groups to find food more quickly and as an “anti-predator device” (Powell and Nickerson 1965).

While C. clypeatus work together to find food they can become aggressive when it comes to shell selection (Spight 1977). The attacking hermit crab will grab onto the back of another hermit crab’s shell and rock the defending hermit crab back and forth. The attacking hermit crab will do this until the defending crab releases its hold on the shell that sparked the conflict (Hazlett 1966). Often the defending hermit crab will chirp, the reason for this is still unknown (Hazlett 1966).

Molting
Hermit crabs must go through a stressful molting process (Sterrer 1986). This process allows for growth and limb regeneration (Wood 2007). There are four stages of molting, pre-molt (proecdysis), molt (ecdysis), post-molt (metecdysis), and intermolt (anecdysis) (Wood 2007).

Proecdysis is the process of laying down a new exoskeleton and storing water for the arduous molt. Ecdysis is the shedding of the exoskeleton, at this point the crab is extremely vunerable without the protection of a hard exoskeleton. Metecdysis is the process of hardening the new exoskeleton; often the crab will eat its old exoskeleton to provide calcium for the new exoskeleton. Anecdysis is the periods in-between molts where the crab gains energy to prepare for the next molt (Wood 2007).

The molting process can take from three weeks to three months depending on the size of the hermit crab (Walker 2005).

Feeding
Coenobita clypeatus is a generalist omnivore scavenger (Morrison 2002). These hermit crabs will eat almost anything from carrion, dead fish, and fallen fruit to rotting wood and sea turtle eggs (Vannini 1976). This feeding strategy is very similar to many other animals, so C. clypeatus is nocturnal to avoid competitors (Morrison 2006). The crab uses its chelipeds to bring food to its mouth parts to be ingested (Kurta 1982).

Reproduction and Life Cycle
Female hermit crabs have gonophores on their fourth pair of legs (Sterrer 1986). Males fertilize the females by passing spermocytes over her gonophores, to do this they must both emerge from their shells slightly (Walker 2005). The female then lays eggs and holds them inside her shell using pleopods (Sterrer 1986). The female broods the eggs for approximately a month before returning to the ocean to release the eggs (Walker 2005). The eggs burst and release zoea, planktonic larvae of Coenobita clypeatus. The zoea remain in the planktos for about two months constantly going through metamorphosis to become a megalopa. The megalopa find its first shell and lives both on land and in the water for a month before completing its first molt. After the molt the hermit crab emerges as a juvenile and is completely terrestrial (Walker 2005).

Threats
Coenobita clypeatus uses its shell to protect its soft body parts from predators and other threats. C. clypeatus is cannibalistic and will eat other hermit crabs especially over shell disputes. C. clypeatus is also known to dig up hermit crabs during molting periods and eat them, often stealing the shell of the molted crab in the process (personal observation). Humans have been attributed to removing shells from the C. clypeatus habitat and can stunt the growth of individuals as well as reduce population size (Nieves-Rivera and Williams 2003).

Recent Research


Much of the current research on Coenobita clypeatus has concentrated on shell selection and competition between land hermit crabs and ants.

Sally E. Walker did a study in Bermuda in 1994 on shell modifications by Coenobita clypeatus. As a paleontologist Walker (1994) was looking at how terrestrial hermit crabs often use fossilized Cittarium pica shells and the problem it caused when trying to establish time lines. C. clypeatus carried shells all over Bermuda making it appear that C. pica lived on land confusing the fossil record. The re-use of shells also can confuse time lines as extremely old shells that have been fossilized for thousands of years, are released by hurricanes and used by present day C. clypeatus. Walker (1994) made a standard way to evaluate C. pica shells to determine if they had been used by C. clypeatus. Walker (1994) also estimated the population of C. clypeatus on Bermuda to be 150 individuals, very different than previous observations made by Haas (1950) when terrestrial hermit crabs were found in large numbers roaming the entire island.

A more recent study tested the patterns of gastropod shell use of C. clypeatus on islands in the Bahamas. Morrison and Spiller (2006) also estimated population densities on these small Bahamian islands. Densities on the islands varied, due to shell availability. Shell use of C. clypeatus appeared dependant on size of the hermit crab. Larger hermit crabs used C. pica shells while smaller crabs used a variety of shells such as periwinkle or nerite shells.

Both studies found a strong correlation between cheliped length and body size. Both studies also suggested that population sizes of C. clypeatus are restricted by shell availability.

Morrison (2002 and 2006) studied the competition between C. clypeatus and ant species. Both species are scavengers and they compete over food sources. The hermit crabs tend to find food quickly but large groups of ants drive the hermit crabs away. The ants can become extremely aggressive and have been known to kill hermit crabs. This competition seems to explain C. clypeatus nocturnal foraging as an attempt at temporal separation from its competitor.

Commercial Importance


Hermit crabs are popular pets in homes around the world. All hermit crab pets are taken from the wild because they can not be bred in captivity.

Bermuda Laws


There are currently no laws in Bermuda pertaining to Ceonobita clypeatus.

Personal Interest


I have several different hermit crab species as pets and they make wonderful companions. They are very easy to care for and are their behavior is very interesting to watch. Each crab has their own personality and I find the social interactions of Coenobita clypeatus extremely interesting. Their communication and relations are fascinating as they work together to find food yet compete with each other for shells. I would love to find a way to breed C. clypeatus in captivity in order to protect the wild populations from being overexploited.

The current state of the C. clypeatus population in Bermuda is alarming. I would like to find a way to bring the plight of C. clypeatus to the attention of the Bermudian Government with the goal of having laws put in place to protect these intriguing animals. I also think it would be beneficial to run a program to increase the population and possibly introduce C. clypeatus to Nonsuch island, the “Living Museum” of Bermuda.

References

Alexander, H. G. L. 1979. A preliminary assessment of the role of the terrestrial decapod crustaceans in the Aldabran ecosystem. Philisophical Transactions of the Royal Society of London Series B 286:241

Ball, E. E. 1972. Observations on the biology of the hermit crab, Coenobita compressus H. Milne Edwards (Decapoda; Anomura) on the west coast of the Americans. Revista de Biologica Tropical 20:265

Chance, F. A. and Hobbs, H. H., Jr. 1969. The fresh water and terrestrial crabs o fthe West Indies with special reference to Dominica. Smithsonian Institute, U.S. National Museum of Natural History Bulletin, 292:1

DeWilde, P. A. W. J. 1973. On the ecology of Coenobita clypeatus in Curacao with reference to reproduction, water economy and osmoregulation in terrestrial hermit crabs. Studies Fauna Curacao 44:1

Fenner, Bob. “Hermit Crabs, Use in the Marine Aquarium Hobby” 1999. WetWebMedia. Accessed 14 November 2007 .

Gould, S. J. 1982. Nature’s odd couples: in Gould, S. J. the Panda’s Thumb: W. W. Norton and Company, New York, p278-288.

Haas, F. 1950. Hermit crabs in fossil snail shells in Bermuda. Ecology 31:152

Hazlett, B. A. 1966. Observations on the social behavior of the land hermit crab, Coenobita clypeatus (Herbst). Ecology 47:316

Hazlett, B. A. 1981. The behavioral ecology of hermit crabs. Annual Review of Ecology and Systematics 12:1

Kurta, A. 1982. Social facilitation of foraging behavior by the hermit crab, Coenibita compressus, in Costa Rica. Biotropica 14:132

Morrison, L. W. 2002. Interspecific competition and coexistence between ants and land hermit crabs on small Bahamian islands. ACTA Oecologica International Journal of Ecology 23:223

Morrison, L. W. 2006. Mechanisms of coexistence and competition between ants and land hermit crabs in Bahamian archipelago. ACTA Oecologica International Journal of Ecology 29:1

Morrison, L. W. and Spiller, D. A. 2006. Land hermit crab (Coenobita clypeatus) densities and patterns of gastropod shell use on small Bahamian islands. J. Biogeogr. 33:314

Nieves-Rivera, A. M. and Williams, E. H., Jr. 2003. Annual migrations and spawning of Coenobita clypeatus (Herbst) on Mona Island (Puerto Rico) and notes on insland crustaceans. Crustaceana 76:547

Osorno, J. L., Fernandez-Casillas, L., and Rodriquez-Juarez, C. 1998. Are hermit crabs looking for light and large shells? Evidence form natural and field induced shell exchanges. Journal of Experimental Marine Biology and Ecology 222:163

Page, H. M. and Willason, S. W. 1982. Distribution patterns of terrestrial hermit crabs at Enewetak Atoll, Marshal Islands. Pacific Science 36:107

Powell, G. C. and Nickerson, R. C. 1965. Aggregations among juvenile king crabs (Paralithodes camischatica Tilesius) Kodiak, Alaskan Animal Behavior 13:374

Randall, H. E. 1964. A study of the growth and other aspects of the biology of the West Indian topshell, Cittarium pica (Linnaeus). Bulletin of Marine Science of the Gulf and Caribbean 14:424

Spight, T. M. 1977. Availability and use of shells by intertidal hermit crabs. Biological Bulletin 152:1

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

Vannini, M. 1975. Researches on the coast of Somalia, The shore and the dune of Sar Uanle, 4, Orientation and anemotaxis in the land hermit crab, Coenobita rugosus Milne Edwards. Monitore Zoologico Italiano, N. S. 6(4):57

Vannini, M. 1976. Researches on the coast of Somalia. The shore and the dune of Sar Uanle. 10. Sandy beach decapods. Monitore Zoologico Italiano 8:255

Walker, S. E. 1994. Biological Remanie: Gastropod fossils used by the living terrestrial hermit crab, Coenobita clypeatus, on Bermuda. Palaios 9:403

Weick, Tammy. “The Life Cycle of Coenobita Clypeatus” 2005. The Crabbage Patch. Accessed 14 November 2007 < http://www.thecrabbagepatch.com/lifecycle.html>.

Weick, Tammy. “Successful Molting” 2005. The Crabbage Patch. Accessed 14 November 2007 < http://www.thecrabbagepatch.com/molting.html>.

Willason, S. W. and Page, H. M. 1983. Patterns of shell resource utilization by terrestrial hermit crabs at Enewetak Atoll, Marshall Islands. Pacific Science 37:157

Wilson, E. O. 1975. Sociobiology. Belknap Press, Cambridge. 697 pp.

Wood, J. B. 2007. Marine Invertebrate Zoology lecture notes.

Links

The Crabbage Patch
Florida Marine Research
Smithsonian Think Tank: Land Hermit Crabs