Red Mangrove Crab – Detailed Guide: Care, Diet, and Breeding

Red Mangrove crab (Pseudosesarma moeshi) is one of the most colorful and interesting crab species in the aquarium trade. So, if you are looking for something unique to add to your paludarium, these crustaceans can be an interesting choice for you.

Red Mangrove crabs are hardy animals and easy to care for, therefore, they can be easily recommended even for beginners.

If you are interested in keeping the Red Mangrove crab as a pet or want to learn more about these interesting creatures, this profile guide will give a special look into this remarkable species.

Quick Notes about Red Mangrove Crabs

Name	Red Mangrove Crab
Other Names	Red-clawed crab, Thai red crab, Aratus moeshi, Long Arm crab, Monas crab, purple Long Arm crab,  Freshwater Red Clawed crab
Scientific Name	Pseudosesarma moeshi (previously Sesarma bidens and Dromia enythopus)
Tank size (minimum)	5 gallons (~20 liters)
Type	Semi-terrestrial
Keeping	Easy
Breeding	Very difficult
Size (carapace)	up to 1.6 inches (4 cm)
Size across the leg span	4 – 5 inches (10 – 12 cm)
Optimal Temperature	71 – 79 °F (22 – 26 °C)
Water type	Freshwater/brackish water
Moisture	70 – 90%
Substrate	Any
Diet	Mostly herbivore/omnivore
Temperament	Semi-aggressive
Life span	up to 4 years
Color Form	Red, black, and orange

Origins, Natural Habitat of Red Mangrove Crabs

Red Mangrove crabs originate from Southeast Asia. They are wildly distributed in Sumatra (type locality Deli), the Mergui Archipelago in the Andaman Sea, Sulawesi, Peninsular Malaysia, and the Gulf of Thailand.

These crabs are semi-terrestrial, living in or near lowland rivers, streams, or swamps, in close vicinity to the ocean and estuaries, with water salinities.

They are dominant components of the intertidal macrofauna of mangrove forests and other wetland ecosystems.

Description of Red Mangrove Crabs

Red Mangrove crabs have a smooth carapace and a square-shaped body. Their eyes are located at the end of two movable eyestalks located in the center of the carapace.

The average size (shell width) of the adult Red Mangrove crab is about 1.2 – 1.6 inches (3 – 4 cm) long. Across the leg span, they can reach 4 – 5 inches (10 – 12 cm).

Coloration:

• Although these brightly colored crustaceans have earned this common name from their red coloration of the carapace, they are not all red. Even more, there are other color morphs and some individuals can be even purplish or dark violet.
• Claws are red. The extreme tips of the fingers are yellow-colored.
• Dimorphism in claws is not present.
• Their legs have almost the same coloration as the carapace.

Lifespan of Red Mangrove Crabs

Currently, there is no data available on the maximum lifespan for Pseudosesarma Moeshi in the wild.

However, in captivity, Red Mangrove crabs can live at least 2 – 3 years, if appropriately cared for.

Typical Behavior of Red Mangrove Crabs

Red Mangrove crabs have a very complex social behavior. On the one hand this is a semi-aggressive and territorial species. On the other, they can be often found in groups.

These crabs have some fascinating personalities. They are not very skittish and readily display aggressive postures towards anything around them.

Although Red Mangrove crabs are primarily nocturnal, they remain relatively active even during the day.

These crabs are not fully aquatic, they are semi-terrestrial and prefer spending more time on land.

Red Mangrove crabs are also amazing climbers. Given the opportunity, they will try to get out of any tank.

These crabs are not diggers in their true sense, but they can push out some soil to make their own dens. In nature, they usually do that at the edge of the water bodies.

They are pretty messy and destructive. Red Mangrove crabs are strong enough to redecorate your paludarium to their liking.

Features:

• Social: No
• Active: Yes
• Peaceful: No (semi-aggressive)
• Burrowers: No (generally)

Feeding Red Mangrove Crabs

Red Mangrove crabs are classified as opportunistic omnivores (because they have adapted to eating both animal and plant material dead or alive). It means that they will eat just about any food they manage to find on the bottom of your tank.

Nonetheless, observations indicated that these crabs do not have a strong preference for high protein food. For the best growth, feeds should contain protein at a level of about 20 – 30% of the diet.

In captivity, Red Mangrove crabs will eat a wide variety of foods including:

• Vegetables.
• Detritus.
• Leaf litter.
• Seeds
• Frozen blood worms.
• Detritus worms.
• Tubifex worms.
• Blackworms.
• Bloodworms
• Earthworms.
• Freshly crushed snails.
• Dead fish or shrimp, etc.

Vegetables and leaves (for example, almond leaves, dead beech, oak leaves, etc.) should always be on the menu, as they feed on these and require the detritus from the leaves. 

Features:

• Diet Type: Mostly herbivorous /omnivore
• Food Preference: Leaves and vegetables
• Feeding Frequency: 3 – 4 times a week

You can also read my article:

• What Do Crabs Eat and How to Feed Them?

How often should We Change the Food?

Crabs are slow eaters. Therefore, you can leave their food for 24 hours before removing it to prevent moles.

Tip: It is best to feed them at night or in the evening because they are nocturnal animals who naturally eat when others sleep. In addition, by doing so you’re recreating natural conditions for your Red Mangrove crabs.

How Often to Feed Red Mangrove Crabs?

Adult crabs should be fed 3 – 4 times a week. DO NOT let them starve or they can start cannibalizing very fast. 

Do Red Mangrove Crabs Need Calcium?

Yes, they do. Even more, calcium is a crucial component of a Red Mangrove Crab’s exoskeleton and overall health.

Calcium can be found in:

• kale,
• broccoli,
• spinach,
• cuttlebones,
• eggshells (dusted),
• figs,
• nuts,
• wonder shells,
• oyster shells,
• seaweed,
• seeds,
• insects, etc.

It is highly recommended to keep a small piece of cuttlefish bone (link to Amazon) in their enclosure all the time.

I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.

Are Red Mangrove Crabs Plant Safe?

It is possible but I would not say that it is absolutely safe to keep them with plants. They may eat or uproot some plants in your tank.

Caring and Keeping Red Mangrove Crabs

Keeping Red Mangrove crabs is not complicated because they do not have special requirements. In addition, this species is a pretty hardy species and can withstand varied ranges of water parameters.

Nonetheless, to make them happy and let them live a long life, we still need to address their core needs!

Tank Size (Enclosure):

Red Mangrove crabs do not require a lot of space. So, a 5-gallon (20 liters) tank can house 1 adult crab. One male and 1 – 2 females may be kept together in the same enclosure of 10 gallons (40 liters).

Males should not be kept in the same tank because of aggression and territorial fighting.

Actually, stocking is one of the most important factors, when it comes to keeping them as pets. Overcrowding is a major source of stress for crabs. In most cases, it leads to health problems, aggression, and cannibalism.

Note: Red Mangrove crabs are known to be able to climb vertical surfaces, and often they use this ability to escape from any tank. So, a tight-fitting lid is essential.

Land vs Water Ratio:

It is very important to remember that Red Mangrove crabs are semi-terrestrial crabs. Even more, they prefer land over water. Therefore, the land area should take at least 70-80% of the space in your tank or even more.

At the same time, water is extremely important as well and there are several reasons for that:

1. Red Mangrove crabs molt (shed their old exoskeleton) in water.
2. Water provides more hiding places and, generally, is a safer place.

Note: It may sound strange but these crabs cannot stay in water for a long time. They will drown!

Water Bowl and Water Type:

Red Mangrove crabs will be completely happy with a suitably sized bowl of water available to them 24/7.

• The water only needs to be a few inches deep. It should be big enough to completely submerge your crab and nothing more. As long as water pools can completely cover their entire bodies, they will be fine.
• It also should have some hiding places. Remember, Red Mangrove crabs molt in the water.
• It is crucial to provide a variety of surfaces for them to get out of the water. You also can place some rocks or driftwood in the water to create small islands that the crab can climb onto.

Red Mangrove crabs are mangrove crabs. In the wild, they have access to freshwater and brackish water. Therefore, it is recommended to provide them with:

• a bowl of freshwater and
• a bowl of brackish (saltwater).

Is it possible to give them only freshwater and skip brackish water? Yes. Of course, it may shorten their lifespan a bit but overall they will be absolutely fine.

How to prepare brackish and freshwater:

Important: Do not ever use simple aquarium salt or table salt to prepare saltwater. You can use only special marine salt (such as Instant ocean marine salt (link to Amazon) or similar).

Your goal is 1.005 to 1.010 SG (up to 12 ppt).

Add about ⅛ cups of salt for each gallon of fresh water in a plastic bucket. Use a good hydrometer or refractometer to take accurate measurements.

1. Stir the water properly.
2. Let it sit for about 20 – 30 minutes.
3. Stir again to ensure that the salt is entirely dissolved and evenly distributed.
4. If the salinity level is high, add more freshwater, and if it is too low, add more marine salt mix.

Regarding freshwater, ideally, you need to give them something like dechlorinated tap water, bottled spring or distilled water.

If you decide to use tap water, let it age for 24 hours before using it. Tap water contains chlorine and it is toxic to them. 

Classic Paludarium Setup

If you do not want to use water bowls and decide to go for a classic paludarium setup for Red Mangrove crabs, you need to know their preferences. These crabs thrive in water with:

pH: a pH range of at least 7.0 – 8.0.
Hardness: KH 0 – 10 and GH 4 – 16.

Related articles:

• How to Set up Paludarium

Pros and Cons of Water Bowls vs Classic Paludarium Setup

Pros:

• All water changes will be very easy and simple.
• Cheap. There will be no need to use any filters.
• Less maintenance.

Cons:

• Water bowls usually do not look great in the setup unless you know how to decorate and hide things.
• Frequent water changes. You will have to replace it every 2-3 days.

Temperature:

The optimal temperature should be in the range of 71 – 79 °F (22 – 26 °C). Red Mangrove crabs like a warm and humid environment.

Tip: If you decide to use a heat pad, it should cover 1/3 (or less) of the tank so that crabs could move from warmer to colder places anytime they want. This allows your crabs to regulate their body temperature to their needs.

Humidity:

Their setup should be tropical in nature with a relative humidity between 70-90%. Humid air lets them breathe properly.

Lighting:

No special requirements. You may not even need one.

However, if you have plants, lighting should be adapted to their needs.

Substrate:

You can have any substrate in their habitat. However, in my opinion, it is better to use some that will allow Red Mangrove crabs to burrow if needed.

Therefore, a mixture of cocofiber and sand will be the best option for them.

Tip: There is a simple trick to test the consistency. Take a pencil and stick it all the way down and pull back up. If the tunnel doesn’t collapse, your substrate is good enough.

The substrate may also require maintenance such as spraying with fresh dechlorinated water on a regular basis in order to keep it moist enough since the moisture in it will evaporate over time.

Important: Do not ever use saltwater to maintain moisture as salt does not evaporate and can lead to a harmful salt build-up.

Decorations and Hiding Places:

Decorations play an important role for Red Mangrove crabs – they provide hiding places (shelter and protection) and minimize their stress. This is especially crucial for the molting process. Cannibalism after molting can become a big problem.

They will appreciate all types of leaves, rocks, wood, PVC pipes, and other decorations to enrich the environment in your tank.

Related article:

• Do We Need Tank Decoration? Simple Ideas

Molt Cycle of Red Mangrove crabs

Periodic molting is vital for the growth of crustaceans. This process is characterized by a complete replacement of the old mineralized exoskeleton with a new one.

This process consists of 4 phases:

1. pre-molt,
2. molt,
3. post-molt.
4. inter-molt.

For more information, read my article “Crabs and Molting Process”.

Important:

• NEVER disturb your crabs when they are molting.
• Do not panic even if you have not seen them for a few days in a row! The molting cycle may extend over days. So, give them time. This is the most stressful moment in their life.
• Keep putting and replacing food in the tank! You never know when they can come up from the molt.
• Keep giving them calcium-rich food.
• Also, do not remove the old exoskeleton from the tank. The crab exoskeleton is multi-layered and consists of calcified chitin, protein, and lots of minerals. Your crab will eat it later.

Rules: How to Care and Handle Red Mangrove Crabs:

• Red Mangrove crabs are not pets you can play with. Do not take them out just because you want to.
• They should never be lifted up by their legs or claws! They can lose a limb by autotomy.
• Do not leave uneaten food for too long. It can cause smell and bacteria in their enclosure. Keep in mind, Red Mangrove crabs can store uneaten food in their burrows. Check them.
• Provide as many hiding places as you can!
• Keep the warm temperature and high humidity.
• The substrate should be based on coconut fiber, soil, and peat to give them a homely feeling.
• Make sure the lid of the tank is closed tightly so that they cannot escape it.

Related article:

• How to Handle your Pet Crustaceans

Sexing Red Mangrove Crabs            

There can be several pointers as well such as:

• size (males are slightly larger),
• coloration (males have intense coloration),
• claws (males have larger and sometimes brighter claws).

However, many of these traits are not completely reliable.

The sure way to tell males and females apart is to look at the underside (abdomen). Males have a narrow and slimmer plate while females have a broad plate on their belly.
Of course, females might also be carrying around some fertilized eggs.

Related article:

• How to Tell If a Crab is Male or Female

Breeding Red Mangrove Crabs

Breeding them is very hard. All available animals are wild-caught.

During my research on this species, a have found only one study describing their larva development through laboratory culture. 

Some facts about breeding Red Mangrove crabs:

• Females can carry up to several thousand eggs.
• In nature, females release free-swimming larvae from the brood pouch into the water, where the larvae are swept by water flow into brackish water lagoons or in the open.
• Their larvae cannot develop in freshwater, they need brackish water (around 15 ppm).
• A warm temperature is preferable (78 – 81 F or 26−27C). It increases their survival rate.
• During their development, they have 4 larvae stages and a megalopa stage.
• After hatching, it takes about 16 days before they complete metamorphosis into a megalopa.
• At the megalopa stage, they reach only 0.04 inches (1 mm) in length.
• They feed on microplankton (Phyto, zooplankton, and freshly hatched Artemia nauplii).
• Water and food should be changed daily.

Red Mangrove Crabs and Suitable Tankmates

Some hobbyists say that this is a very sociable and also peaceful animal. Well, maybe they just got lucky.

Red Mangrove crabs are usually better in solitary confinement. Even though they are not very aggressive (compared to most crab species), they are still not completely peaceful and inoffensive.

If you decide to keep them in a group, you need to understand the risk. It is very important:  

• Red Mangrove crabs should be kept in groups of one male with 1 – 2 females.
• Males, in particular, are extremely likely to fight and eventually kill one another when housed together.

• The tank should have lots and lots of hiding places. They need to have hiding places even in water!
• They should be well-fed at all times.

In a paludarium setup, it is possible to keep dwarf shrimp and fish with them. Red Mangrove crabs do not show a big interest in going and staying in the water for a long time.

Bad Tank Mates: 

• Any crayfish species.
• Other crab species.
• Snails.
• Frogs.

In Conclusion

Red Mangrove crabs are low maintenance and simple species to care for.

These crabs are semi-terrestrial and do not require large tanks, therefore, even beginners will be able to keep them without problems since they are hardy and undemanding.