Crabs can be an enchanting and pleasant addition to your saltwater aquarium. Not only do they look great and add interest, but they also help to keep your reef tank clean! In my aquarium, my platoon of Scarlet Hermit crabs are some of my favorite inhabitants. They are just so unique!
Here are some of the most popular species of crabs for a saltwater aquarium:
- Mithrax Crabs
- Anemone Crabs
- Sally Lightfoot Crabs
- Halloween Hermit Crabs
- Pom Pom Crabs
- Arrowhead Crabs
- Scarlet Hermit Crabs
- Coral Crabs
You can choose to buy from a massive crab variety in our hobby so let’s get into a little detail about some of the most popular crabs you will find while perusing your local fish store.
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The Mithrax crabs (Mithrax sculputus), also known as Emerald crabs have very glossy green bodies and are very easy to care for. They generally like to hide in dark corners during the day and are very much nocturnal, but with a good food supply, you find them munching away during the day too.
These crabs are very popular as they have a habit of eating algae, especially bubble algae. Bubble algae are also known as Valonia and Ventricaria can grow very quickly and can block drains and inlets of pumps ( Trust me I almost found out the hard way!)
To help with the battle of Bubble algae buy the females as they tend to stay more focused and here is a quick video I made on how to easily sexy a crab:
Mithrax crabs are mostly omnivores so they need a lot of green food like dried seaweed if your aquarium is very clean or bare of naturally growing algae. They can be aggressive sometimes and can begin to prey on other tank members when don’t get ample food supply. You will also find them devouring any dead animal it finds.
Most Mithrax crabs thrive in a mature reef tank with ample food sources and plenty of rock to hide. The majority of Mithrax crabs stay small all their life but a few have been seen to grow quite large, especially in a large aquarium. When they get large they can be dangerous to other invertebrates and fish in the tank so it is better to remove them if they start to show signs of aggression
They are capable of growing 2 inches in size and can be bought for around $10.
Anemone crabs (Neopetrolisthes ohshimai) are known as the cool crustaceans because they are very pretty with brilliant color. Belonging to Porcellanidae family these crabs have a red polka dot pattern on their shells with white edges which give them a look of porcelain, hence why they are sometimes known as a Porcelain Crab.
They have very large claws which they use to hold large meaty pieces that they find, but most of the time they use their fan-likes appendages to catch microscopic food from the water column.
These crabs are very passive and can be kept in pairs. They generally do not show aggressiveness towards other tank dwellers but can raise their large claws to ward off any potential predators when needed.
They are named after anemones that they live within the wild. They can be kept easily without anemones in the home aquarium, but having an anemone will show this symbiotic relationship well.
These crabs can reach as big as 2-3 inches in size and their price ranges from $10 to $20 each.
Sally Lightfoot Crabs
Sally Lightfoot crabs (Percnon gibbesi) belong to Grapsidae family. These crabs have a very striking appearance with a brown body and yellow, red rings on their legs. They are a great tank janitor, cleaning the tank from unwanted organic material.
These crabs are omnivores and scavengers. They feed on detritus, algae, uneaten food, and everything else that comes in their path. If they are given the opportunity they will eat meat, such as other invertebrates and fish. In a new, unmatured tank you can boost their diet with dried seaweed and meaty pieces like Mysis Shrimp, Clams, etc.
They are usually semi-aggressive when small but when getting larger they can get very aggressive and intolerant. These crabs do fine when put in with larger fish but with smaller fish, they can show aggressiveness and harm them or eat them, although they don’t attack corals.
They favor places where they can camouflage themselves easily so they will be in need of a lot of rocks in their aquarium. They also move very quickly which is why they are very hard to catch. These guys are very undemanding.
Their sizes range to 3″ and you can find them for around $20. These can be found in blue, orange, yellow, and brown.
Halloween Hermit Crabs
The Halloween Hermit Crab (Ciliopagurus strigatus) belongs to Diogenidae family. They are very beautiful to look at and will remind you of the Halloween decorations you had as a kid.
They are a vibrant orange color with red stripes around their legs which makes a nice contrast from the shell. They are very easy to care for as they are omnivores, scavengers, and algae eaters. They will eat detritus, dead organisms, leftovers, cyanobacteria, and algae making them a useful member of your tanks’ clean-up-crew.
If you are keeping them in a young and unmatured aquarium, feed them with shrimp and dried seaweed to help them from starving. They are mostly safe to keep but sometimes they can be aggressive and try to steal food from corals and knock them over in the process once they start to get larger.
As with all hermit crabs they live in shells so make sure you have an extensive supply of different sized shells so they can ‘Move Home’ whenever they feel ready. I just pick up a few shells each time I go to the fish store and drop them in the back of the tank. It is not uncommon for the Hermit Crabs to attack and eat snails to get to their shells if they cannot find a suitable empty one.
For one adult Halloween Hermit Crab, you should have a tank of 15-20 gallons, and be sure you provide plenty of rocks in your tank as these are mainly nocturnal creatures that like to seek refuge within the rocks.
Their sizes range up to 3″ and price range is usually between $12-16.
Pom Pom Crabs
These crabs are very cute, unique, and mystifying crustaceans. Their color ranges from white to tan with dark markings all over their body which helps them camouflage better.
They belong to the genus Lybia and are called the Pom Pom Crab because it looks like they hold pom poms in their hands, not really, they are used to catch floating food from the water.
The pom poms that they are holding are actually anemones, either from the Triactis or Bunodiepsis species. These anemones protect them against any potential predator and the crabs will wave their anemones to show that they are not the next meal! They also use this anemone for collecting food.
They are very easy to care for and are safe with fish and other pom crabs making them great for additions to a reef tank. They are omnivores and mostly eat zooplankton, but if you are keeping them in a young tank feed them with a variety of food like pellets, brine, and Mysis to help keep them fat and happy.
They are small at around 1 inch in size so can be difficult to see in a large tank, but in a smaller tank, you will have no problem finding them. Another interesting fact about them is that they molt like other arthropods so don’t worry if you see something that appears to be a crab’s dead body lying on the sand bed
Their price ranges from $24 to $39
The Arrow Crab (Stenorhynchus spp.) are commonly called spider crabs, belong to the family Majidae. Their color ranges from cream to yellow with iridescent white and blue stripes and the shape of head and body gives it its name.
These crabs are the most controversial ones because on one hand they look fascinating and on the other, they look like something from an alien or horror movie! They are easy to care for but have territorial and opportunistic predatory nature meaning these are mostly carnivores so it is better to keep them well-fed to prevent them from targeting your livestock.
They are effective in controlling bristle worm infestations but are not the best choice as an addition to a new, unmatured aquarium. They are aggressive towards their own species so it is recommended to have only one crab per tank and having a lot of rock will allow it to hide when it feels threatened.
These crabs are nocturnal and patrol the aquarium at night but once settled you will find them out during the day just doing their thing. They can grow up to 6 inches so it is better that you put them in at least an aquarium of 20 gallons and they do molt like all other crustaceans so don’t get scared that your crab is dead!
Their price ranges from $17 to $40
Scarlet Hermit Crabs
Sometimes known as the Scarlet Reef Hermit Crab, these vivid little critters belong to the family Diogenidae. They are one of the most common crabs as part of an aquarium’s cleanup crew because they are so easy to keep and are far less aggressive compared to the Blue Leg and Blue Knee Hermit crabs.
These crabs are herbivores and are voracious algae eaters, although they are not expected to keep your tank algae free! If you are planning to keep them in your aquarium you should provide them with empty shells and feed them with dried seaweed in a new tank with very little natural food growing in it
They live peacefully with other aquarium members but you have to take caution while adding them to the tank as large fish can prey on these little things. These are perfect for all sizes of aquariums as they are only 1/2″ to 1″ in size and being able to house multiple together makes them a great interesting crab to own!
They are cheap to buy with their price range from $1 to $6!
Also commonly known as the Pocillopora Crab, Acropora Crab, or Acro Crab these crabs predominantly live on branches of stony corals Acropora and Pocillopora but will be seen on just about any coral.
There are of a variety of colors with varying color pigments all over their body, ranging from blues, to purples to pinks, making them a very contrasting and pretty crab to watch.
Some coral crabs are very beneficial while some try to eat fellow fish when they get bigger. The good ones that you need to look for are related to Tetralia and Trapezia species. They have a symbiotic relationship with corals as they provide them protection from any potential predators and corals in return provide them with food and shelter.
These crabs can be a little hard to identify because they look different at every stage of their lifecycle so if this is a crab you want to be sure to get pictures of them at varying ages so you can easily identify them in the fish store.
These crabs are carnivores so in an aquarium you should provide them with meaty food particles, although they also eat mucus off of corals. They will need a host for surviving so make sure your aquarium is mature enough and has some established coral for them to inhabit
They only reach up to 1 inch so make great additions to nano tank and larger aquariums and be sure to not mistake them for a hairy Gorilla crab (Xanthid spp.) who will completely eat your corals!
You can buy these crabs for around $30.
Which Crabs are Reef Safe?
Crabs that can generally be considered reef-safe are Anemone Crabs, Halloween Crabs, Pop Pom Crabs, Scarlet Hermit Crabs, Red & Blue Leg Hermit Crabs, Pocillipora Crabs, Horseshoe Crabs & Zebra Reef Hermit Crabs. Be sure to secure coral frags well as some crabs will knock them over as they move around.
There are exceptions to the norm, but in general, all the crabs mentioned above do well in an aquarium containing any type of coral. To ensure crabs do not prey on your coral it is always advised to keep them well-fed with their preferred meal of choice.
Which Crabs Eat Algae?
Crabs that eat algae in a reef tank are Mithrax Crabs, Blue & Red Leg Hermit Crabs, Scarlet Hermit Crabs, Red Flidler Crabs, Zebra Reef Hermit Crabs, Halloween Hermit Crabs, and Porcelain Crabs. Herbivore carbs should be added to a mature aquarium with sustainable algae growth to keep crabs fed.
Once an aquarium is 6 months old then it should be mature enough to sustain herbivore crabs. If you are unsure that there is sufficient food growing naturally within the aquarium you can supplement their diet with Nori or sinking algae pellets.
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Which Crabs Eat Detritus?
Crabs that eat detritus in a reef tank are Mithrax Crabs, Blue & Red Leg Hermit Crabs, Scarlet Hermit Crabs, Red Flidler Crabs, Zebra Reef Hermit Crabs, Halloween Hermit Crabs, Horseshoe Crabs, Sally Lightfoot Crabs, and Arrow Crabs. Crabs are great for removing detritus built up in tight spaces.
A broad selection of omnivore crabs will ensure all areas of the aquarium are kept free of detritus. High water flow and a diverse selection of crabs help to ensure detritus does not allow it to build, break down, and cause high nitrates.
Do You Need to Feed Crabs in a Reef Tank?
Crabs added to a mature aquarium usually find enough of their natural food while scavenging. Many crabs will also feed off food fed to the fish ait it passes them or lands close by. For new, unmatured aquariums sinking pellets or blended/powdered coral foods will help supplement their diet.
The trick is to try and feed the aquarium without too much being uneaten and left to decompose. Feeding small and often will help prevent this but if the aquarium is new this leads to a problem of undernourished crabs.
Spot-feeding a crab with pieces of Mysis shrimp or Nori via a feeding tube of turkey baster will help ensure the crabs remain well-fed until there is enough of their natural food growing within the aquarium.
Do Crabs Need Dry Land in a Reef Tank?
Most saltwater crabs do not need an area of dry land in a saltwater aquarium. In their natural habitat, they live solely underwater on the natural coral reefs. The Striped Shore Crab does need dry land but this requires a very specific type of aquarium outside the scope of most saltwater aquarists.
This is one of the most famous saltwater aquariums designed with this species of crab in mind:
How Many Crabs Can I Have in a Reef Tank?
The number of crabs you can keep in a reef aquarium varies based on its volume. For small tanks under 55 gallons 1 crab for every 3-5 gallons is recommended, while for larger tanks many aquarists recommend a diverse group of crabs based on 1 crab for every 2-5 gallons.
These are general rules of thumb and the aquarist is advised to use caution and slowly add crabs as needed. Adding 50 crabs to a brand-new 100 gallon aquarium is a guaranteed way to ensure most end up dead.
Instead buy a select group of various crabs and add them. In a few months see how the cleanliness of the tank is and add some more if needed. The crab and snail population must meet the growth of their natural food source or they will become hungry and could begin to prey on fish and corals.
Crabs are a great and recommended addition to every reef aquarium! Not only do they add great contrast, diversity, and personality to the aquarium, their large appetite makes them an essential part of the tanks’ clean-up-crew.
A selection of different crab species will help to target different food groups allowing your tank to help maintain acceptable levels of detritus and nuisance algae.
Be sure to add crabs slowly as many of the large ‘Reef Cleaner’ packages you see advertised work well when first added, but once their food supply begins to run out, many starve and die.
If you found this article helpful I highly recommend you read these too:
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- 19 Best Corals For Beginners – With Pictures
- 20 Best Saltwater Fish For Beginners – With Pictures
- 14 Saltwater Fish To Avoid As A Beginner
- Best Beginner Clams For A Reef Tank