Photo credit: Glenda Vélez Calabria (Colombia)     Technical review: Abdel Rahman El Gamal

This photo was taken in mundo marino and te mostramos lo que pasa en el fondo, Colombia

General: This species is a large marine hermit crab which was originally described as Cancer diogenes. These crabs which are red in color may show sexual dimorphism in regard to size whereas males are heavier than their female counterparts; the average wet weights were reported to be about 95 g and 50 g for males and females, respectively. Also, the claw size is another example of sexual dimorphism whereas the right claw is greatly enlarged in males suggesting male-specific functions such as defensing self and territory as well as mating.

Distribution and habitats: The distribution of the giant hermit crab occurs where its preferred warm temperature, proper salinity and depth are available. While the crab juveniles can be found both inshore in estuaries, their adults do generally occur offshore or around inlets and near-shore reefs.

The species is found on muddy, sandy, and shelly bottoms at depths that could range from near-shore to more than 100 meters; turtle grass beds and in the mangrove areas are examples.

Feeding habits: The giant hermit crab preys on a variety of other invertebrates, and feeds on macroalgae.  Because of its opportunistic behavior, the species does likely occur where a continuous flow of feeding opportunities do exist.

Predators: In spite of their large size, the giant hermit crab could be preyed upon by some predators such as the Kemp’s Ridley sea turtle, the nassau grouper, and large bony fishes, rays, and octopus.

Reproduction and life cycle: The giant hermit crab reproduces sexually in which the male spermatophore is transferred to the female who clutches the fertilized eggs on her abdomen throughout the embryonic development. Hatched larvae pass through different planktonic stages with a duration range of about 30-80 days depending on food availability and water temperature. Afterwards, and through the metamorphosis, the juvenile crab is produced. Juveniles must select larger gastropod shells of the most appropriate size and shape in which they live and continue to grow.

Giant hermit crabs and their associates: The species is an example of obligatorily associated organisms whereas benthic juveniles must find an appropriately-sized host of marine gastropod snail shell in which they continue to grow. As they grow, the crabs continue looking for larger shells to fit their growing bodies. Because of their large sizes, the discarded shells of large mollusks such as the Queen Conch and the tulip snails are favorite hosts to the crabs.

The giant hermit can also be associated with other invertebrates; the hermit crab anemone, the porcelain crab, and the zebra flatworm are examples. Some of these associations such as the anemones, the crabs provide mobile shelter to the anemones that are attached to the shells of the crab. This is in addition to obtaining food as well as reducing the competition from other anemones. In turn, the anemone affords the crab camouflage and some degree of protection, via its stinging tentacles, from potential crab predators such as octopus.