Are Emerald Crabs Reef Safe?

Are Emerald Crabs Reef Safe?




The Emerald Crab is known as a scavenger invertebrate and will feed on uneaten foods and nuisance algae such as hair and bubble algae. Actually, the Emerald Crab is one of the rare members of a cleanup crew that will eat bubble algae. These crabs are very distinct and have a flat shiny green body and hairy legs.

The Emerald Crab loves to hide in rocks and caves during the day. You will see them mostly at night but not always. It requires a well-established aquarium with plenty of rockwork and hiding places. Once comfortable in your tank, the Emerald Crab will fairly active climbing all over the rocks picking on algae. They are very interesting to watch.

Of course, if you currently have a saltwater reef tank or plan to keep corals with Emerald Crabs, you will need to know if they are reef safe.


What does reef safe mean?


When you see the term reef safe, this refers to any livestock (fish or invertebrates) that are compatible with corals that may be present in your reef aquarium. Livestock that is not reef safe refers to fish and inverts that can be harmful to live corals and should not be mixed together.

Some livestock are considered reef safe with caution. In this case, the fish or invert may be reef safe but there is a chance that they could be harmful to corals. Sometimes there is no guarantee that a particular fish will not harm corals. It can be hit or miss if a certain fish or invert is labeled reef safe with caution. The Flame Angelfish is a good example.


Emerald Crabs In Reef Tanks – Are They Reef Safe?


Yes, Emerald Crabs are considered reef safe. I always have them in my reef tanks and have never seen them bother anything. You might see different opinions online with respect to them being reef safe but for the most part, Emerald Crabs will pick around the coral on the rocks or if its a frag on a plug. But I have never noticed them bother the actual coral itself.



are emerald crabs reef safe


Are Emerald Crabs Peaceful?


Emerald Crabs are considered semi-aggressive. For the most part, you won’t have a problem with them bothering other livestock. I have heard stories of them attacking smaller fish and other invertebrates at night. They have been known to go after small snails. I have never experienced that myself but anything is possible I guess.

I grabbed a pic of the Emerald Crab in my 120-gallon reef tank.


How many Emerald Crabs Per Tank?


Emerald Crabs only reach a size of 2″ when full grown and can live up to 4 years. They can be mixed together in the same tank and generally won’t fight with each other. It is recommended to have no more than 1 Emerald Crab for every 20 gallons tank size. If you have a small tank no less than a 10 gallon, you can keep 1 Emerald Crab.

Emerald Crabs are very hardy and can do well in less than ideal water conditions. When you first get them home, make sure to acclimate them properly so they can adjust to your tank’s conditions. They may hide for a while at first but then will become active after a short period of time.

One thing to be cautious of with Emerald Crabs. If you have Coraline algae in your tank and would like to keep it, it’s probably best to only have 1 Emerald Crab in your tank. They are known to eat some Coraline algae from time to time.

Emerald Crabs are easy to purchase and are affordable. You can buy them online for about $10 each at