What Kind of Crabs Can Continuously Live Under Water in an Aquarium?

A number of attractive and interesting aquatic crabs are suitable for inclusion in the marine aquarium. Most of these species will feed on unwanted algae in the aquarium and are sought after by most aquarists. The majority of these aquatic crabs are small, although the strangely shaped horseshoe crab can attain a much larger adult size. Aquatic crabs are generally hardy and easy to keep.

  1. Pom Pom Crab

    • The pom pom crab is native to the Indo-Pacfic. This little marine crustacean exhibits a unique behavior by sourcing and carrying a tiny anemone in each of its claws. Anemones possess stinging cells on the tips of their tentacles, and the pom pom crab protects itself by thrusting them toward would-be predators. These crabs will also drag their anemones across the reef and then remove some of the food items that the anemones have captured. Some food particles are left for the anemone to consume, and in this way pom pom crabs ensure the health of their personal anemones. These small, inch-long crabs are attractively marked, exhibiting striped legs and vivid body colors. The pom pom crab is a hardy crustacean which can be housed in small groups in the aquarium. Females carry their reddish-colored egg masses on their abdomens.

    Scarlet Hermit Crab

    • These peaceful little crabs are sought after by marine aquarists, as they feed on a variety of nuisance algae types, including slime, hair and filamentous algae. Scarlet hermit crabs will also feed on cyanobacteria, which can plague an aquarist if allowed to get out of hand. These small crabs, which are found on coral reef environments in the Caribbean, are just over an inch in length. Scarlet hermit crabs are easy to care for in an aquarium, as they will readily accept tiny pieces of frozen seafood items and dried seaweed. These crabs require progressively larger shells as they grow, and an ongoing supply of empty shells must be provided by the aquarist.

    Green Emerald Crab

    • Green emerald crabs are immediately identifiable by their vivid green body. These small marine crabs eat not only leftover food in the aquarium but also feed on bubble algae, which many hobbyists are not easily able to remove. Green emerald crabs are found on coral reefs in the Caribbean, where they forage for food items during the hours of darkness. This little marine crab tends to hide during the day among coral rubble and requires similar décor when kept in an aquarium. Green emerald crabs will readily accept dried seaweed and tiny pieces of prawn or calamari when in captivity. These crabs will also accept sinking aquarium pellets.

    Horseshoe Crab

    • Horseshoe crabs are living fossils which have remained effectively unchanged for 250 million years. These light tan crabs are demersal or bottom-dwelling creatures which burrow into the soft substrate in estuaries and tidal flats. The adult female horseshoe crab, which is larger than the male, has a top shell 12 inches in diameter. Both sexes possess a modified tail, in the form of a long spike. Horseshoe crabs keep the aquarium substrate clean and aerated by sifting through the sand particles in search for food items.