Coral reefs are rich, biodiverse ecosystems that are home to incredible creatures of all shapes and sizes. Scuba divers from all over the world flock to remote locations like the Similan and Surin Islands, South Andaman in Thailand or Mergui Archipelago in Burma, and to have the chance to catch a glimpse of marine curiosities from massive manta rays to tiny nudibranchs scattered across underwater landscapes that will take your breath away. If you are the kind of person who is enthralled by macro life, you have surely heard of the harlequin shrimp.
| Also called Hymenocera Elegant, the Harlequin Shrimp is a minuscule flamboyant crustacean that is among the superstars of its family. Its hypnotic coloration and bizarre behavior are some of the reasons that this rarity is high on the list of Macro-life Under Water photographers (read the full Underwater guide to diving Thailand). |  |
Spotting a harlequin shrimp
Harlequin shrimp can be identified by some distinctive features such as the unique body shape and appendages. Their claws are large and flat, different from all other types of shrimp. Their tail is trapezoidal and they use two fancy flat antennae on their heads with sophisticated scent receptors tuned to detect prey.
How big do harlequin shrimp get
The females can grow up to 5cm in length whereas the males, even fully gown, looks like a juveniles next to them.
One of the Harlequin Shrimps most attractive feature is their Carnaval-ready costume. Their carapace is cream-colored patterned with large psychedelic spots.
It used to be thought that there were two varieties of harlequin shrimp (Hymenocera elegant and H. Picta) but it was later concluded that they are one and the same with variations in color depending on the region they inhabit.
One of the Harlequin Shrimps most attractive feature is their Carnaval-ready costume. Their carapace is cream-colored patterned with large psychedelic spots.
It used to be thought that there were two varieties of harlequin shrimp (Hymenocera elegant and H. Picta) but it was later concluded that they are one and the same with variations in color depending on the region they inhabit.
| Around the Indian Ocean (H. Elegant), they generally have orange to purple spots surrounded by a blue line. While Harlequin shrimp native to the pacific, particularly from Hawaii (H. Picta), are the most vibrant with spots that are rather pink or purple detailed with a yellow lining. |  Hawaiian Harlequin Shrimp. (H. Picta) Native of the Pacific |
Can harlequin shrimp change color?
Some aquarium owners have reported that Harlequin shrimp can change color base on their mood and as an example, one ordered a pair one picta, and one elegant, both arrived looking identical in color until they both calmed down and returned to their true colors!
These intricate motifs have developed through evolution as a means of protection. In the underwater world, animals with bright colors are usually recognized by potential predators as toxic. This is true for the harlequin shrimp whose advantage invites far fewer natural predators than other less colored creatures of similar stature.
These intricate motifs have developed through evolution as a means of protection. In the underwater world, animals with bright colors are usually recognized by potential predators as toxic. This is true for the harlequin shrimp whose advantage invites far fewer natural predators than other less colored creatures of similar stature.
Harlequin Shrimp and juvenile (H. Elegant)
Home sweet hiding hole
 | Harlequin shrimps live on and around coral reefs between 1 and 30 meters deep. These shy creatures tend to prefer dark narrow crevices and branched corals to seek refuge from the jaws of the fish, crabs, and octopus that prey on them. |
They are often found in pairs and if a couple successfully establishes a secure den they can be found in the same place together for long periods of time. Sometimes Harlequin Shrimps will even spend the vast majority of their 7-year lifespan in the same place and with the same mate. They will live, breed, hunt, and defend their territory together loyally as long as their surroundings allow them. You may be thinking this is a very romantic gesture on the part of these gorgeous couples. Sorry to burst your bubble, but this behavior might just be a good way to increase their chances for the female’s eggs to get fertilized...
Romance in the style of a harlequin shrimp
Like many crustaceans in general, harlequin shrimp moult when they outgrow their shells leaving them soft and exposed. This sloughing allows the renewal of the exoskeleton and marks the moment when a female reaches sexual maturity. She will be roughly 200-240 days old when she undergoes her first molting period and then repeats the process every 18-26 days for the rest of her life. Following every shedding of her carapace, she will be fertile and ready to reproduce.
During the breeding season, the female can produce between 100 and 5000 eggs which she will carry attached to her abdomen following fertilization. This may seem like a staggering number but most of the young will not survive their next stage of development. Basically, the more babies that hatch the more chances that some will survive to sexual maturity and continue to propagate the species.
During the breeding season, the female can produce between 100 and 5000 eggs which she will carry attached to her abdomen following fertilization. This may seem like a staggering number but most of the young will not survive their next stage of development. Basically, the more babies that hatch the more chances that some will survive to sexual maturity and continue to propagate the species.
 Juvenile of Harlequin Shrimp | After 12-18 days of gestation, the larvae emerge from their eggs extremely small and vulnerable ready to begin the 5-6 week settlement period. If they can find a safe place to grow during this time the larvae will develop into their awe-inspiring mature form. |
What do harlequin shrimp eat?
Harlequin shrimp have very unique dinning habits that could easily be inspiring for the plot of a horror movie. Although they are very small, they survive on a diet of almost exclusively live starfish much bigger then themselves. With a particular taste for their legs and soft tissues (best eaten with a nice chianti). Most seas tars species are suitable but reportedly Harlequin shrimp cannot eat brittle stars.
"Are Harlequin Shrimp fetishist?" |  |
How do harlequin shrimp kill starfish?
The mating pair will hunt together, sharing the tasks at hand. They will first have to track down their prey using their sensitive antennae. Males, although much smaller, have been known to be more agile and proficient with this hunt than the females. Once the starfish is caught, the pair of harlequin shrimp will work as a team to flip the starfish over and then drag it back to their den using their powerful pincers. Unable to move, the starfish’s tube-like feet are exposed for its captors to feast on while it’s still alive.
A curious harlequin shrimp and starfish relationship
Even more gruesome is the harlequin shrimp’s tendency to prolong the starfish’s misery by feeding it for up to two weeks’ time to keep it alive and fresh. Some starfish will try to put up a fight by shedding the limb that is being eaten and regrowing a new limb to replace it. Unfortunately, the echinoderm is often too weak to effectively regenerate tissues. This is probably a blessing in disguise, as this effort would essentially give these twisted shrimp further opportunity to extend its prey’s torture.
In moments of desperation, the harlequin shrimp will resort to eating the similar soft leg tubes of sea urchins. It is clear that this is not their choice food source as they will only resort to this should the only other option be starvation.
In moments of desperation, the harlequin shrimp will resort to eating the similar soft leg tubes of sea urchins. It is clear that this is not their choice food source as they will only resort to this should the only other option be starvation.
Harmony on the reef
If you look past the freaky aspects of the harlequin shrimp’s food fetishes, there are actually benefits on a grander scale. The fact that their picky palate only has a taste for sea stars, including the species that eats coral has nurtured an important symbiotic relationship with the reef. The corals provide shelter while the shrimp will slowly help control the starfish population which could be extremely problematic should it grow out of hand.
Species like the crown of thorns starfish can devastate healthy coral colonies if there aren’t enough natural predators to keep their numbers under control. Although harlequin shrimp populations aren’t dense enough to eradicate these pests, they still do their part to fend off these destructive creatures who put their living habitat in jeopardy.
Species like the crown of thorns starfish can devastate healthy coral colonies if there aren’t enough natural predators to keep their numbers under control. Although harlequin shrimp populations aren’t dense enough to eradicate these pests, they still do their part to fend off these destructive creatures who put their living habitat in jeopardy.
Harlequin shrimps are in danger
 | Like many other marine creatures, harlequin shrimp are suffering due to the intervention of humans in their environment. Global warming, pollution, coral bleaching events, changes to water chemistry, and fishing to name a few, are factors that threaten this gorgeous species. |
| The deterioration of coral reefs could have a devastating impact on this species as they will not have the protection to help them develop and thrive. Also with fewer corals come fewer starfish for harlequin shrimp to eat, and thus begins a vicious cycle of doom. Although there are no specific conservation initiatives targeting harlequin shrimp, coral conservation projects can indirectly benefit individuals living on a reef that is well cared for. |  |
In recent years with the growing aquarium trade, these beauties have also become a major target for people wishing to put them on display in their personal fish tanks. When you search the internet for information on harlequin shrimp, the majority of hits are from sites offering information to aquarium breeders and collectors, which is heartbreaking. The appeal is understandable from an aesthetic standpoint, but we would much prefer to observe them happy and free in their natural habitat. We often get the opportunity to spot them tucked away in the reefs while diving Myanmar and Thailand
Although harlequin shrimp may have questionable dietary practices, we still find them to be magnificent little critters and look forward to every chance to meet them under the seas.
Although harlequin shrimp may have questionable dietary practices, we still find them to be magnificent little critters and look forward to every chance to meet them under the seas.
HARLEQUIN SHRIMP CLASSIFICATION
| Kingdom: Animalia Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca Order: Decapoda Infraorder: Caridea Family: Hymenoceridae Genus: Hymenocera Species: Hymenocera Picta and Hymenocera Elegant |  |
For the moment Myanmar's borders remain shut and all our cruises this season are planned to be in Thailand.
We are hoping for a reopening before next season...
We are hoping for a reopening before next season...
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