Description

The Crabs belong to the “crustaceans”. There are about 6,800 different species in total. They have a more or less hard carapace made from calcium carbonate. They have eight legs used to move and two claws in the front used for hunting or defense, more or less large depending on the species, two eyes and a shell. Most of the crabs are aquatic but some of them are terrestrial. In Mauritius, more than 23 different species have been found, on earth and underwater.

What about the species living in mauritius?

To start with an easy one to spot for you as a beginner diver would be the “spotted porcelain crab”. We can usually find it in anemones, sponges or corals and their size is between 3 and 7 cm. They can be spotted between 5m depth to 20m depth. Very often seen on our dive site Ti Koraye.

Another crab that can be spotted mostly by night is the “splendid pebble crab”, who lives from 1m depth to 30m depth. His size is about 15-20cm and with its red carapace, red eyes, and large teeth it’s easily recognizable. If you know what to search you might be able to see it at Merville Patches.

Now, we just wanted to show you the “marbled stone crab” which can measure 6 to 10 cm, and lives until 95m depth. This specie is still very little known, it has not been studied a lot and still has a lot to tell us.

I wanted to show you the amazing “Calappa calappa” or "smooth box crab". As you can see, with its white eyes out of its orange carapace, its folded claws which fit perfectly under its shell, the kind of comb with teeth on the top of its claws, it looks particular and different from many other ones. It is called “calappa” which comes from “kelapa” the Malay word for “coconut”. It is active at night and when it feels threaten it can burrow beneath the sand.  

If you take a closer look into the corals, you might also find the one crab belonging to the “Trapezioidea” superfamily. This family includes small but fascinating crabs often found living symbiotically within coral colonies. These crabs, typically less than a few centimeters in size, use their compact, rounded bodies and strong legs to navigate the intricate branches of corals. Their colors often match their host corals, providing them with excellent camouflage.

Unlike many free-roaming crabs, members of "Trapezioidea" play a vital role in reef health. They defend their coral hosts from predators such as starfish and nudibranchs and help keep the coral surface clean by feeding on mucus, detritus, and small invaders. This mutualistic relationship highlights the delicate balance of reef ecosystems, where even the smallest creatures contribute to the survival of entire coral colonies.

Easily recognizable by its large, smooth carapace adorned with striking maroon or purplish spots, “Carpilius maculatus”—also known as the "marbled reef crab"—is a fascinating nocturnal inhabitant of coral reefs. Found throughout the Indo-Pacific, including the waters of Mauritius, this species prefers rocky and coral-rich environments where it can blend into crevices during the day.

Unlike smaller reef-associated crabs, Carpilius maculatus has a more robust build, with strong claws capable of breaking open mollusk shells.

Small but resilient, “Cymo quadrilobatus” —also known as the "blue-eyed coral crab"— is a cryptic crab species often found nestled within coral colonies. This tiny crustacean belongs to the Xanthidae family and is commonly associated with branching corals, where it finds shelter and food. Its compact, somewhat rounded body features distinct lobes on the carapace, giving it its scientific name.

Despite its small size, "Cymo quadrilobatus" plays a role in the reef ecosystem. It feeds on algae, detritus, and sometimes coral mucus, helping to maintain the health of its coral host. However, in cases of environmental stress, it may also contribute to coral tissue damage.

Commonly known as the "horned ghost crab", "Ocypode ceratophthalmus" is a fast-moving, nocturnal inhabitant of sandy beaches across the Indo-Pacific. It gets its name from the elongated, horn-like projections on its stalked eyes, which give it excellent vision to detect predators and prey.

This crab is a master of speed and stealth, capable of sprinting across the sand and disappearing into its burrow in seconds. It plays a crucial role in coastal ecosystems by feeding on organic debris, small invertebrates, and even scavenging on dead fish. At night, it emerges from its burrow to patrol the shoreline, leaving behind intricate patterns of footprints and tiny sand pellets as it searches for food.

Finally, you can also observe the flat crab called “Percnon guinotae” or "Shore crab".  With its flattened body and long, slender legs, it is built for speed, allowing it to dart across rocky surfaces with ease. This species is known for its striking coloration, often featuring shades of brown, red, and blue, which help it blend into its surroundings.

Unlike many crabs that rely on scavenging, it has a more herbivorous diet, feeding primarily on algae. Its presence in marine ecosystems plays a crucial role in maintaining algal growth and promoting habitat balance. Divers and snorkelers may catch a glimpse of this fast-moving crustacean along reef edges, where it thrives in high-energy environments.

A special thank you to Visham and Guillaume for their amazing pictures of crabs! :)