Common name: Common Hermit Crab

General Information

The Common Hermit Crab, scientifically known as Pagurus bernhardus, is a fascinating and resourceful crustacean widely distributed across the northeast Atlantic Ocean and adjacent seas. This species is well-known for its unique habit of occupying empty gastropod shells to protect its soft abdomen, a behavior that has earned it the "hermit" moniker. Its adaptability and intriguing behavior make it a popular choice among marine hobbyists.

In the wild, Pagurus bernhardus plays an important ecological role by recycling shells and scavenging detritus, contributing to the cleanliness of its environment. In captivity, it serves as an excellent "clean-up crew" member, helping to manage algae and leftover food in marine aquariums. Its hardy nature and low maintenance requirements make it an ideal addition for beginners and experienced aquarists alike.

Physically, the Common Hermit Crab is characterized by its reddish-brown coloration, with lighter bands on its legs and claws. Its asymmetrical claws are a distinguishing feature, with one claw being significantly larger than the other. This species can be confused with other hermit crabs, but its coloration and size help differentiate it from similar species.

Care

Caring for Pagurus bernhardus is relatively straightforward. These hermit crabs thrive in well-established marine aquariums with stable water parameters. They require a sandy or mixed substrate to mimic their natural habitat and provide them with a surface to explore. Live rock is also beneficial, offering hiding spots and additional foraging opportunities.

Providing a variety of empty shells of different sizes is crucial for their well-being. As they grow, hermit crabs will need to "upgrade" to larger shells. A lack of suitable shells can lead to stress and aggression among tank inhabitants.

Diet and Feeding

The Common Hermit Crab is an omnivore and a scavenger, feeding on detritus, algae, and leftover food in the aquarium. In captivity, they can be offered a diet of high-quality marine pellets, algae wafers, and occasional treats like chopped seafood or blanched vegetables. Their natural scavenging behavior makes them excellent at cleaning up uneaten food, but supplemental feeding ensures they receive adequate nutrition.

Feed them small portions once or twice a day, observing their behavior to avoid overfeeding. A varied diet helps maintain their health and vibrant coloration.

Behavior and Compatibility

Pagurus bernhardus is generally peaceful and coexists well with other reef-safe species. However, they can be territorial when it comes to shells, occasionally engaging in "shell fights" if suitable options are scarce. Providing an abundance of empty shells can minimize such conflicts.

These hermit crabs are active and entertaining to watch, often seen exploring the substrate and climbing over rocks. They are compatible with a wide range of tank mates, including fish, corals, and other invertebrates. However, caution is advised when housing them with small or delicate species, as they may inadvertently cause harm while scavenging.

Symbiosis

While Pagurus bernhardus does not have a specific symbiotic relationship like some other hermit crab species, it often carries epibionts such as algae or small anemones on its shell. These hitchhikers can provide camouflage and additional protection, creating a mutually beneficial arrangement. In captivity, these relationships can add an extra layer of interest to the aquarium.

Health and Common Issues

The Common Hermit Crab is a hardy species, but it can be susceptible to stress from poor water quality or a lack of suitable shells. Regular water changes and monitoring of parameters such as salinity, pH, and temperature are essential to their health.

When selecting a hermit crab, look for active individuals with intact legs and claws. Avoid crabs that appear lethargic or have visible damage to their exoskeleton. Providing a varied diet and a stress-free environment will help prevent common health issues and ensure a long, healthy life.

Habitat

In the wild, Pagurus bernhardus inhabits rocky shores, sandy bottoms, and seagrass meadows, ranging from the intertidal zone to depths of over 100 meters. It is commonly found in the northeast Atlantic, including the North Sea, Baltic Sea, and Mediterranean Sea.

This species prefers environments with ample hiding spots and a variety of shells to choose from. Replicating these conditions in captivity helps them feel secure and exhibit natural behaviors.