Cleaner shrimp make everyone smile, but videos show they don’t mind making those smiles even brighter.
These industrious invertebrates eat parasites and dead skin off fish, keeping them healthy and earning a meal. But when human divers approach them the shrimp are happy to clean them up, too.
Why do shrimp do this for us, and should we let them?
While on vacation on Hideaway Island in Vanuatu, Victoria Kronsell of Melbourne, Australia, filmed a dive shop employee getting a quick clean from a skunk shrimp at sunken tugboat teeming with clownfish.
Kosnell didn’t try it herself, but “it’s a good little trick for the tourists,” she says.
It’s also pretty common thing for divers to try, says Benjamin Titus, of the American Museum of Natural History in New York City who has a studied the effects of diver interaction on cleaner shrimp.
Shrimp have very poor vision, he says, which might explain why they don’t shy away from human clients.
Shrimp might see a diver slowly approaching shrimp’s cleaning station as “just a large client fish,” says Eleanor Caves, a postdoctoral researcher at Duke University.
In a recent study Caves showed that shrimp even tried to clean darker shapes on an iPad screen placed against their tank—fish turn darker to signal shrimp they want cleaning, not dinner. (Related: Secret code prevents cleaner shrimp from cecoming a meal)
The presence of divers can also affect cleaning behavior.
In a 2015 study, Titus and his team observed cleaning activity at two dive sites, one devoid of people, the other a popular dive site.
While cleaning behavior—among fish and shrimp—didn’t change when observed with just cameras, it declined by half at the popular dive site when humans were present. When divers visited areas typically free of humans, it stopped altogether. These findings show fish may acclimate to diver presence, but not entirely.
Being motionless and exposed to the water column during cleaning leaves fish more vulnerable to predators than usual and the presence of a diver at a station might cause fish to put off cleaning to the detriment of their own health and that of other fish.
“By occupying a cleaning station, a diver may be scaring off or physically blocking clients that need cleaning,” says Caves.
Don’t hold your breath
Caves has never had a shrimp teeth-cleaning either, though they’ve cleaned her hand in the lab when she’s doing routine tank maintenance.
“They’re so small you can really barely feel them, except for occasional sharper pokes when they dig in a bit with their chelae,” pincer-like claws, so she thinks teeth cleaning would be a strange feeling.
“It’s great when people gain a broader understanding of what’s actually on a reef,” Caves says, but “the best practice for divers, and anyone out enjoying nature, is to leave animals alone.”
Divers will find that if they sit quietly in the right place they’ll likely see cleaning take place with minimal disturbance to the animals.
Titus recognizes the fun of the interaction but doesn’t encourage getting a crustacean cleaning.
Besides, he says, the first rule of diving is “don’t hold your breath,” which can increase the risk for decompression sickness, known as “the bends.” And “that is exactly what you’re doing when you’re letting a shrimp crawl through your mouth.”