The Emerald Crab Diet

The emerald crab, also called the jade crab and mithrax crab, is a large-bodied, bright green crab native to the tropical areas of the western Atlantic Ocean. It is found in the Florida Keys and the Caribbean, and prefers rocky coast lines, seagrass beds and backwaters. These crabs are popular in the pet trade, and are often used to remove algae from reef tanks.

  1. Algae

    • Emerald crabs eat primarily algae, and spend most of their time on algae-covered coastlines. They may also be found anywhere that algae grows heavily on rocks and debris in or near the ocean. These highly ornamental crabs are also used to control nuisance algae species in reef tanks, particularly bubble algae. According to the Journal of the Marine Biological Association of the United Kingdom, these crabs are more effective at algae control when fed tiny frozen shrimp than when fed commercial feed pellets.

    Scavenging

    • Smaller crabs stick primarily to an algae diet, but as they grow, these crabs also begin to scavenge other food types. They also consume cyanobacteria, dead animals, ocean and tank detritus and seaweed. In captivity, these crabs remove organic material before it can rot, keeping the tank free of undesirable micro-organisms.

    Size

    • According to the Doctors Foster and Smith website, emerald crabs are relatively small creatures, growing to about 3 inches. They are semi-aggressive, and that aggression increases as they grow. Aquarium owners may wish to choose fish too large to serve as prey for the crab in order to reduce the chance of one species killing another. Crabs that receive adequate food from their environment are less likely to become a problem, even at a large size.

    Considerations

    • Emerald crabs may not be appropriate for small-scale algae infestations, as they spread this organism while consuming it. These crabs tear the algal cells apart, spreading cell liquid full of juvenile algae into the water. The Journal of the Marine Biological Association of the United Kingdom suggests that this behavior may contribute to additional algae growth.

    Misconceptions

    • This species of crabs is sometimes misrepresented as vegetarian. However, the emerald crab is actually omnivorous, and will scavenge dead animals and food left by other animals. Larger specimens can become predatory, and may consume small aquarium animals or coral. Maintaining higher algae populations and supplementing the crabs' diet with additional vegetation may help prevent this.