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Crabs: Cute and Quirky Crustaceans that Help Tank Maintenance 


Scientists have insurmountable evidence that a lot of crustaceans evolved into crab-like forms. The term ‘Carcinisation’ has been coined to signify this massive drive of crustaceans to become pincered scuttlers.

With over 6700 different species spread across all of Earth’s oceans, lakes, and tropical coasts, crabs are one of the most recognized creatures in the world. What makes these consummate survivors such great saltwater aquarium additions? Saltwater crabs are a large group of invertebrates within the decapod crustaceans family, consisting of several sub groups.  From hermits, stone crabs, porcelains, sally light foot, anemone crabs, mithrax to name a few.  This wide range of invertebrates can vary in size from small to very large.

They are Scavengers That Clean the Tank

Crabs commonly found in and around coral reefs are bottom dwellers.  We are often asked what do crabs eat? Most crabs peruse the ocean floor, reefs, and rocks for food ranging from algae, organic matter, carcasses, and waste. Popular crab species for saltwater aquariums are chosen for their affinity for different waste that could clog up filters, cause algae to spread, or make tank water murky. This makes them extremely handy as they could save you $1000’s in clean up and filter change over time.

There are different species of crab with varied diets. Some of the most popular crabs target some aggressive forms of aquarium algae. Algae species like the hair algae or bubble algae tend to spread fast and suck the nutrients from the water.  Many people want to know if saltwater crabs can live in freshwater.  The answer is no - if saltwater drops below specific gravity equal to or lower then 1.017, most saltwater inverts will die.

For tanks prone to issues with algae blooms, the Emerald crab reigns supreme. This crustacean is a 10-limbed Roomba. The Emerald crab is constantly browsing every crevice and reef for algae, these stunning crabs particularly love to graze on bubble algae. If your tank is prone to bubble algae or you are just coming out of a flucanazole flush to kill all algae, introduce an emerald crab and you can forget about new outbreaks. 

Similarly, the Hermit Crab is a great tank addition. These omnivorous scavengers are one of the most common aquarium additions. They will graze the bottom of the tank, gulping down any left-over plant and animal matter that your fish missed during a feed.

Blue-legged Hermit crabs are small, which allows them to reach the spaces between rocks and corals in the tank and siphon off the algae that grow in the smallest crevices. This makes them extremely useful as they feed on both algae and the organic matter that algae grow on. This unique combination stemming from their omnivorous diet makes them an extremely powerful algae deterrent.

Great Personalities

Crabs are unique and great to observe. Each species has its own unique movement, behavior, courtship rituals, and habits. This makes them great to observe and study and kids love watching these pincered decapods sieve through the substrate. 

Species like the hermit crab chooses a shell and makes it it’s home. It uses the shell for protection and camouflage from above as they focus on rock crevices in search of algae. 

The anemone crab nestles itself amidst the venomous anemone tentacles (anemone crabs, like the clownfish, are immune to the anemone sting) and raises the fan-like filters behind its pincers and uses like a net to catch floating organic matter in the currents. By raising these ‘fans’ into the flowing current, they catch small bits of food which they then pick off using their pincers. This behavior is fascinating to observe.

The Scarlet Reef Hermit Crab is an extremely active species that sifts through substrate all day using the incredibly cute front mandibles and mouth parts. They are like a plow cutting through large swathes of the tank bed every day in search of debris. They also shed their shell when they find a newer, better shell and if there are multiple Scarlet Reef Crab in the tank, they often exchange their shells which is a unique trait that is awesome if you are lucky enough to observe it.

Attractive Tank Additions!

Most marine crab species sport a range of colors, patterns and have their own unique look. They blend in well with their tank mates and add a pop of color and movement to the reef bed, which is usually filled only with fish activity. 

The Porcelain Anemone crab (Neopetrolisthes maculatus) formerly referred to as Neopetrolisthes ohshimai, indigenous to the indo-pacific waters but are now widely regarded as ‘aquarium regulars’ across the globe. They sport a distinctive red polka dot pattern on a bright white shell body. This makes them an instant tank attraction. They also have one of the most unique feeding patterns in the marine world which makes them very fun to observe.

The Electric Orange Hermit Crab is one such attractive species, sporting bright neon orange stripes on the legs and body. They look extremely snazzy when they are relaxing with just their banded feet sticking out from under their shell. 


Make sure you fill your tank with shells in a lot of different sizes, shapes, and color. Picking an assortment of shells from Aquarium Depot ensures that the crabs in your tank have a great selection to choose from and find the right shell. 

Also, species like Emerald Crabs and Anemone Crabs suffer when the tank is running low on algae. It is crucial to substitute their diet with dry seaweed and algae feed. The Sea Salad feed from Aquarium Depot is a great blend for algae-dependant crabs. 

Some crabs also tend to be slightly aggressive towards snails. This is because they are a constant war for shells, which is a currency in the reef ecosystem. Also, they tend to get aggressive towards some shrimp and even fish if not well-fed. But in general, barring few anomalies, crabs tend to mind their own business, scavenging for food in the tank. 

Make sure your next saltwater aquarium addition is a crab! They are easy to care for, hardy decapods that will clean your tank for you and add much-needed character and color. Who can imagine a reef setup without crabs? Not us! 


These crustaceans are well known for their fondness of algae, detritus and left over food and waste, making them a great solution for the home aquarium for excess food and waste removal.  However most of the crabs in the trade are omnivores and will eat whatever is available to sustain life.  Care must be given when choosing invertebrates for your aquarium to insure that claws are not large enough to catch small fish and other small invertebrates.