The Emerald Crab is one of the most popular algae-eating invertebrates used in saltwater reef aquariums. Recognizable by its green coloration and compact body, this active clean-up crew member spends much of its time picking through live rock in search of algae, leftover food, and organic debris.
Emerald Crabs are especially popular with reef keepers because of their reputation for eating bubble algae (Valonia). While individual feeding behavior can vary, they can be a valuable part of a diverse saltwater aquarium clean-up crew.
Emerald Crab Care
Scientific Name: Mithraculus sculptus
Common Name: Emerald Crab / Emerald Mithrax Crab
Type: Marine Crab / Clean-Up Crew
Care Level: Easy
Temperament: Generally Peaceful
Reef Safe: Generally Reef Safe
Diet: Omnivore / Algae Grazer / Scavenger
Adult Size: Approximately 2–2.5"
Aquarium Area: Rockwork & Crevices
Water Temperature: 74–80°F
Salinity: 1.023–1.026 SG
Recommended pH: 8.1–8.4
Do Emerald Crabs Eat Bubble Algae?
Emerald Crabs are commonly added to reef aquariums as a natural way to help control bubble algae. They may pick individual bubbles from rockwork while grazing and can reach areas that are difficult to clean manually.
However, not every Emerald Crab will eat bubble algae, and they should not be considered a guaranteed solution to an outbreak. Managing nutrients, removing accessible bubble algae, and maintaining a diverse clean-up crew are still important for long-term control.
What Do Emerald Crabs Eat?
Emerald Crabs are opportunistic omnivores. In addition to nuisance algae, they may consume film algae, leftover fish food, detritus, and other organic material found throughout the aquarium.
If natural algae becomes limited, supplemental feeding is recommended. Dried marine algae, algae-based sinking foods, pellets, and occasional meaty marine foods can help keep the crab well fed.
Are Emerald Crabs Reef Safe?
Emerald Crabs are generally considered reef safe, particularly when appropriately fed. Most spend their time grazing rockwork rather than bothering healthy corals.
As with many opportunistic crabs, individual behavior can vary. A hungry or larger Emerald Crab may become more likely to investigate other food sources, so adequate feeding is important in very clean reef systems.
Like other marine invertebrates, Emerald Crabs are sensitive to rapid changes in salinity and water chemistry. Careful acclimation and stable reef parameters are recommended.
Why Add an Emerald Crab to Your Clean-Up Crew?
The Emerald Crab provides a different style of algae control than snails and hermit crabs. Its ability to pick through cracks and crevices in live rock makes it a useful addition to a balanced clean-up crew.
For reef keepers dealing with nuisance algae—particularly bubble algae—Emerald Crabs are one of the most commonly selected clean-up crew invertebrates.
Emerald Crabs are also included in our Island Reef Aquatics Large Invert Pack, alongside other algae grazers, scavengers, and sand-bed cleaners.
Available from Island Reef Aquatics with local pickup in Deltona, Florida and shipping available.
