Emerald Crab Care (Clean-Up Crew Hero)

Emerald Crab Care (Clean-Up Crew Hero)


Its scientific name Mithraculus Sculptus, or Emerald Crab, is one of the most famous clean-up crew additions for saltwater aquariums but they do come with some baggage.

The Emerald Crab care routine is fairly straightforward but it isn’t exactly the most reef-safe crew mate around. Take a look at some of our tips on caring for your little crustacean below.

How do you care for Emerald Crabs?

Proper crab care is actually super easy as they will adapt to aquarium life really well and aren’t that picky about their environment. However, water quality should be sitting at something similar to what is listed below. 

  • Specific gravity: 1.023 to 1.025
  • pH levels: 8.0 to 8.4
  • Water temperature: 72 to 82 degrees Fahrenheit 


Fairly simple and a decent range to meet the lax demands of these little crabs. Otherwise, the most important thing you can do is ensure that they have adequate supplies of food every day so they do not become famished and begin feasting on your tank’s inhabitants.

Emerald Crabs are known to eat reef polyps if they become hungry enough so checking in on your crabs to ensure that they are fed properly can save you potential frustration later.

These little guys also love live rock so make sure they have some that make little caves they can hide in during their molting process. You might have live rock but all the unique hiding spaces may already be taken up by the current tank inhabitants.

Always make sure your crab has some space of its own.

Why did my Emerald Crab die?

First I have to ask, did your Emerald Crab actually die? It is very possible that your crab only molted its old shell and is currently hiding until it has a new layer of protection grown. 

If your Emerald Crab has passed away and it appears to be the only casualty then there are a few things to consider. These are just some of the most common ways that your crab might have passed away. 

Water Parameters

Double-check that your water parameters are within an acceptable range. It is possible that there was a swing in the night and your crab didn’t make it. 


Look for marks on your crab’s shell to see if they might have been suffering from an infection or disease. If you see that this might have been the case, remove the crab immediately so that it won’t continue to be a health risk to the rest of your tank’s ecosystem. 

Tank Mate Feud

Have you noticed that one of your larger fish has been antagonizing your Emerald Crab? It is possible that the fish finally had enough and attacked the crab.


How old was your Emerald Crab? They typically only live between 2 and 4 years so it might be possible it was just the end of their life.


Always watch what you are introducing into your aquarium’s water supply. Many medicines can have copper or other metal in them which are toxic to Emerald Crabs. 

How many Emerald Crabs per gallon?

Since these little guys don’t get too big you might assume that you can have a bunch of them to eat all of your bubble algae but that isn’t the case. The crab needs space to do its thing so you should try to keep the population to one Emerald Crab per 20 to 30 gallons of water. 

Emerald Crab tankmate compatibility

Emerald Crabs, as we have discussed, can be a little aggressive to their tankmates depending on their comfortability but there are some species that they will tolerate better than others.  They will attack small creatures like snails and other crabs. If you already have bottom feeders to reduce the bubble algae in your tank, it might be best to avoid introducing crabs to the same ecosystem. The bottom feeders will be easy targets for the crabs. 

You want to stick to fish that are non-aggressive and will stick to the middle and top ranges of your saltwater aquarium. Of course, on the other side of the spectrum, there are the fish that are too big as that will only reverse the roles and make the crab a target. 

The best way to ensure the safety of your reef and the other inhabitants of your tank is to give the crab plenty of food to keep it satisfied. If the crab is full, they will be much less likely to attack other species in the tank. 

Do Emerald Crabs eat hair algae or bubble algae?

Emerald Crabs are big eaters and the main reason to have one introduced to your tank’s community is to cut down on the bubble algae present. Emerald Crabs will eat bubble algae and hair algae! They will help clear up your tank in no time but remember that if you do not have adequate bubble algae in your tank, to begin with, it might be a good idea to consider a different species to help reduce algae, or else you will need to be sure to supplement the crab’s diet with dried seaweed or pellets.

What else will Emerald Crabs eat?

Emerald Crabs are big eaters and will pick at anything if they are hungry enough. Whether it is leftover food, algae, or even its own shell the crab will snack whenever it needs sustenance. They are scavengers after all. However, that doesn’t mean that you should just let your crab fend for itself in your reef tank. You should be providing a regular supply of food so that you prevent your crab from wanting to mess with your reef. 

If you have a lot of algae, which is the entire reason that you invested in an Emerald Crab in the first place, you might be thinking that it will be fine to just let the crab nibble on the algae every day. I caution you against relying solely on your algae supply to feed your Emerald Crab population. The moment that there aren’t sufficient algae for your crab they might very well begin moving towards your reef or smaller creatures in your tank. A well-fed crab is a happy crab who won’t bother his fellow tank mates.

If you want to introduce a supplemental diet to your crab, then a diet of pellet foods or dried nori will suffice. If your tank has sufficient algae then you might consider feeding your Emerald Crabs the pellets only a couple of times a week. 

Are Emerald Crabs reef safe?

Yes and no. It depends on a few things whether you Emerald Crab will get along with your reef. The first thing you want to consider is if your Emerald Crab is fed enough. The species is known to become a little upset when they are hungry and will lash out for food wherever they can find it. 

However, some people report that crabs are more hostile depending on the type of aquarium setup you have. An SPS setup for instance has been reported to attract the little crabs by some aquarists, despite being fed.

The most important things you can do if you are still interested in introducing an Emerald Crab into your reef tank is to make sure they are properly fed and to monitor them closely. After a week or two, if the crab is doing well and you are feeding them properly without any issues, they should be okay and given a little more trust. 

Are Emerald Crabs hardy?

You may be on the fence about purchasing an Emerald Crab for your saltwater tank but rest assured that the little green cleaners are a hardy bunch. They can withstand a little bit of negligence but you should always be doing your best to give them a habitat that will allow them to thrive the best. 

How big do Emerald Crabs get?

Emerald Crabs are tiny. They will reach around 2 inches but it is possible they could be slightly bigger or smaller than this size. It all depends on variation within the species. We don’t say all people will reach  5’11 after all.

Do Emerald Crabs molt?

Yes, Emerald Crabs like other types of crustaceans do molt as they grow so they can replace their shell with one that fits their expanding body better. So as you are inspecting your saltwater aquarium in the morning don’t be confused and think that your Emerald Crab passed away in the middle of the night. They will leave their shell behind and go find a place to hide in the reef until they have a replacement shell. How frequently your crab will molt will depend on the environment that it is living in. 

How long do Emerald Crabs live?

With the proper crab care, crabs can live anywhere between 2 to 4 years. Just be sure that you are paying attention that they are adequately fed, their tank mates are not antagonizing them, and their water parameters are within the proper range and you should have no issue keeping these little guys alive for their expected lifespan. 

Final thoughts

Now you have all the best tips you need for your Emerald Crab care routine. Though they aren’t necessarily the most reef-safe option available, they are one of the hardiest and least picky clean-up crew members available. They add a nice splash of color and personality to your tank as long as you ensure that they are properly cared for. The biggest worry you may have with one of these crabs is if it begins to antagonize your reef or its fellow tank mates but the best way to handle a situation like that is proper feeding. Keep a nice reserve of dried seaweed and/or pellets so that you can properly supplement the crab’s diet throughout the week. That way they won’t even have the thought to take a nibble out of your reef.

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