Banded Coral Shrimps – A Dance, a Wave & Maybe a Nice Massage

A pair of banded corals work from inside a vase sponge at Roatan Island, off the coast of Honduras.

BANDED CORAL SHRIMPS MAY BE THE FRIENDLIEST CREATURES ON THE REEF.  Well, they’re always waving at us.

Waving, that is, their super-long white antennae trying to attract passing divers – okay, passing fishes, actually – to come over for a little close-up cleaning. With their prominent tentacles, red-and-white banded bodies and outsized claw limbs, they’re high-profile members of the fish-cleaning profession that’s also inhabited by anemone shrimps, cleaning gobies and other little (often-juvenile) fishes.

Found in tropical waters around the world, banded coral shrimps (Stenopus hispidus) are keratin-shelled crustaceans. As decapods, they have five pairs of walking legs, three of them affixed with claws. The clawed, red-and-white banded middle pair is so enlarged and angular that, in my mind, anyway, the little guys remind me of hulking transformer robots. But smaller, and always mugging for the camera.

Like all of the thousands of species of shrimps, banded corals have elongated abdomens that, in jucier cousins, are the parts we find tasty and edible. With S. hispidus, very thin and only as long as 2.5 inches/6 centimeters, no such luck.

COME-HITHER SIGNALS

The shrimp beckons.

Banded coral shrimps whip their antennal appendages around from under ledges, from inside vase sponges and crevices and, sometimes, out in the open on seafloor substrates. They’re often somehow fixed upside down on the underside of a ledge, with their bodies mostly hidden and the antennae jutting out with a come-hither allure.

When a promising fish, or host, comes by, they do a little dance, swaying their bodies and antennae from side to side to make the prospect of a hook-up more enticing. Since the antennae can be three times the length of their bodies, it’s a noticeable bit of advertising.

THE DEAD SKIN SOCIETY. ALSO, PARASITES

As the fish moves in close, the shrimps use their claws to pick stuff off of the fish’s skin. What is it they clean, exactly? Tiny stuff: parasites, bacteria, fungi and dead or damaged skin tissues.

Cleaning activity appears to offer two mutual benefits: the shrimps, in the best hunter/gatherer tradition, fulfill their dietary needs while providing the fishes with healthy and apparently enjoyable services to the fish.

Just to be clear: S. hispidus is perfectly willing and able to also dine on other crustaceans, snails, worms, zooplankton and even small fishes. Apparently, bristle worms are a great delicacy. Somewhat shy and reclusive during the day, they’re more active at night when they leave their ledges and move out onto the reef to forage.

There are several YouTube videos showing banded coral shrimps eating bristle worms. The folks who posted this one, apparently shot in an aquarium, intended it as a comedy but it provides an excellent demonstration of the shrimp’s eating technique.

CLEANING STATION ETHICS

S. hispidus’ willingness to dine on small fishes does kind of go against the ambiance of cleaning stations (the term for apparently recognized sites where cleaning is regularly done). Host fishes – that is, the clients being cleaned – pretty much universally respect the principle that cleaning shrimps and fishes are benign service providers and not lunch. They’re routinely granted access to the insides of host fishes’ mouths and gills without being devoured.

Sometimes they do venture a little ways out in the open.

BANDED CORAL SHRIMP FACTS

Banded coral shrimps have been observed at depths as far down as nearly 700 feet/210 meters but since their typical cleaning clients are shallow water fishes like tangs, grunts, groupers and eels, they’re most likely to be found in at 40ft/9m or less.

As arthropods, they have three-part bodies, with the head and thorax fused together and covered by wide, flat plates called carapaces. They have exoskeletons based on keratin, like the stuff that makes up your fingernails. Like all arthropods, they periodically have to molt, or shed that exoskeleton, in order to grow.

As decapods, they differ from lobsters and crabs by having thin, somewhat fragile legs made for perching rather than crawling. In addition to their five pairs of legs extending from their thoraxes, their abdomens bear fringe-like appendages called pereopods (swimmerets) that they use for swimming. Although hard to discern, their bodies are covered with short spines that provide a defensive advantage.

Perhaps because their services are so important to the health of the reef and its assorted denizens, S. hispidus has no known natural predators on the reef. If a claw should break off for some reason, it can be regenerate with the next molt.

A visual cacophony of feelers.

TRUE SHRIMP LOVE

Banded coral shrimps are singular among invertebrates in that they’re monogamous – they mate for life (which is typically two to three years). You won’t find a bunch of banded corals together, but you’ll usually see two. They share.

Reproduction is tied to the female being newly molted. It starts with a courtship dance by the male, who transfers a sperm sack to the female. She inseminates her eggs and sticks them to her legs for some 16 days of incubation. Newly hatched little shrimps remain attached to Momma Shrimp for about six weeks before moving off into the plankton.

The author of this YouTube video found these guys on a reef. It does a great job of showing the female with her clutch of eggs attached to her abdomen.

Once settled, they also have a love for home. They’ll spend their lives in and defending territories less than two meters in diameter.

GIVE IT A TRY BUT WATCH THE REEF

Theoretically, if you’re slow and careful you can extend your hand toward a banded coral cleaning shrimp and persuade them to come out and clean your fingernails. I’ve succeeded in doing this with seafloor-based anemone shrimp but the difficulty with banded corals is that their locations make it a challenge to remain stable for the time required. Usually there’s a current, so you have to be careful not to crash into the reef. Don’t crash into the reef.

Sometimes, you just know they’re there.

PRINCIPAL SOURCES:   Marine Biology, Fourth Edition, Peter Castro, Michael Huber; Stenopus hispidus, Encyclopedia of Life; Banded Coral Shrimp, World Association of Zoos and Aquariums; Banded Coral Shrimp, Dutch Caribbean Nature Alliance; Banded Coral Shrimp, Marine Species Identification Portal; Reef Creature Identification, Florida, Caribbean, Bahamas & Reef Creature Identification, Tropical Pacific, Paul Humann, Ned DeLoach.

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