Reef Safe Critters Explained - Reef Safe Crabs

Crabs For The Reef Aquarium

Crabs are an essential part of any healthy reef aquarium and careful consideration must be taken when figuring out which type, and how many of these critters you will have. Below you will find a list of reef aquarium crabs that are available for placement in your tank with a description, and photo of each.

Blue Legged Hermits (Phimochirus operculatus):

The tiny Blue Legged Hermit Crab is one of the favorite scavengers and aquarium cleaners on the market today. Their beautiful coloration, small size, aquarium hardiness and excellent reef compatibility make them perfect additions to your reef aquarium. They are small enough to get into tight holes in the rock to scavenge on detritus, algae and other organic matter that larger invertebrates can’t reach. The common blue legged hermit crab, as its name states, has bright blue legs and reaches sizes up to about ?” in length. In a reef aquarium, it is advised to have at least one blue legged hermit crab for ever two gallons of aquarium water. This quantity is a suggested minimum; however, if you plan to have only this species of crab as your cleaner crew, you might require more.

Important note: If you have a large amount of any shell dwelling crab in your aquarium, it is necessary to provide them a large assortment of shells that they can move into as they grow. If you have no extra shells in your tank, they will fight over the shells you do have and they will kill each other in the search for new homes.

Scarlet Hermit Crabs (Paguristes cadenati):

By far, my favorite reef aquarium scavenger is the Scarlet Hermit Crab. The coloration of these little crabs is amazing, and their ability to clean a tank is just as spectacular. Like most other reef aquarium crabs, these little guys feed on algae, detritus and other organic waste present in the aquarium. They are great at cleaning hair algae off of rocks and substrate, but they will also feed on left over fish food, cyanobacteria and will actively scavenge on dead aquarium inhabitants. They require minimal maintenance in an established reef aquarium, but they might need to be provided additional food such as seaweed or extra fish food if your tank is extremely clean. Scarlet Hermit Crabs eat voraciously but only reach maximum lengths of about 1.5” in.

Some refer to these crabs as being very docile and nonaggressive, but I have personally seen them attack each other to steal new homes (shells); being so, I would classify the scarlet hermit crab as moderately aggressive. With this said, I have added a large amount of empty shells to my reef tank and have had ended the battles for new homes.

Green Emerald Crab (Mithrax Sculptus):

Green Emerald Crabs are a great addition to any reef aquarium cleaner crew. They feed on nuisance algae like hair and bubble algae as well as on meaty foods and organic material. They are very attractive crabs with shiny green bodies and hairy legs. They have flat tipped pinchers that they use to grasp algae and other foods with, and, when startled, they use their pinchers to put on quite a ferocious display.

Although they eat algae and detritus as the main part of their diet, I have, on occasion, caught mine picking polyps off SPS corals and even off of Purple Gorgonians. They hide by day in rock crevasses and come out to graze on algae at night in the relative safety of darkness. It is recommended to keep one Emerald Green Crab per 20 Gallons of aquarium water and to feed them regularly if they are not in an established reef aquarium.