As a frequent diver in the clear waters of Bonaire, I have become obsessed with observing the little creatures that reside there. Among my favorites are the colorful shrimp. Some species are found on certain coral, and many live in stinging anemone. Some feed on tentacle tissue of their host and on the mucus-trapped planktonic particles adhering to it. But many feed on external dead tissue, algae and parasites found on fish. The shrimp advertises its service by swaying its body and waving its antennae. Such cleaners even enter the mouths of fishes and clean behind gill covers with impunity.
How can those that live in anemone tolerate the stinging cells of their host? The exoskeleton of a shrimp does not provide full immediate automatic protection. Rather, anemone shrimp have to acclimate to their hosts. When a ‘non-acclimated’ shrimp contacts an anemone, the cnidarian’s tentacles (as a result of the stinging nematocysts) will adhere to the shrimp, causing it to rapidly jump backward and attempt to tear itself away.
An acclimating shrimp will endure the occasional sting and will gingerly make contact with the anemone’s tentacles and pick at the integument of its potential host. Once it has fully acclimated (in one to five hours) the shrimp can move about the anemone unimpeded, and the host will not respond at all to the presence of the shrimp.
What happens during this acclimation process that inhibits nematocyst discharge? One theory suggests that the shrimp accumulates sea anemone mucus on its exoskeleton, which serves to camouflage it. A second theory is that the shrimp build up chemicals in their bodies that inhibit the discharge of the stinging cells of sea anemones during acclimation. This chemical is retained and possibly even secreted from a gland. Whatever the mechanism, there is a remarkable additional fact: If a shrimp is isolated from an anemone for as little as 24 hours, it loses its protection and has to re-acclimate to a specific host!
Here are some of my favorite shrimp:
The Spotted Cleaner shrimp (Periclimenes yucatanicus) lives among the tentacles of several species of sea anemones and exhibits the typical behavior to attract client fish. It grows to a length of about one inch. It has transparent body patterns with brown and white saddle-shaped markings. The chelae and legs are boldly striped in red, purple and white. There are two pairs of long white antennae banded in black.
Breeding takes place in the summer and females have been seen brooding eggs under their abdomens in the months of July and August. After hatching, the larvae pass through several planktonic stages before settling on the seabed and undergoing metamorphosis into the adult form.
Squat shrimp or Sexy shrimp (Thor amboinensis) lives symbiotically on corals, sea anemones and other marine invertebrates in shallow reef communities. It is a small shrimp growing to a length of about 0.5 inch. It is an olive brown color with symmetrically placed white patches edged with thin blue lines. It characteristically carries its abdomen curved upwards with its tail fan above its head.
Thor amboinensis does not clean fish, but feeds on tentacle tissue and on the mucus-trapped planktonic particles adhering to it.
The female Thor amboinensis carries the fertilized eggs under her abdomen until they are ready to hatch. The zoea larvae pass through several stages and, before undergoing metamorphosis, are attracted by both chemical cues in the water and visual cues which cause them to settle near potential host anemones.
Pederson’s shrimp (Ancylomenes pedersoni) is often associated with a sea anemone, at depths of three to 49 feet. It is a small transparent shrimp with bluish and violet markings on the body and long white antennae and within its range is unlikely to be confused with other species.
Up to 26 shrimps have been found associated with one sea anemone but usually there are just one or two. The shrimp offers cleaning services to passing fish in the typical antennae-waving fashion.
Scarlet-striped Cleaner shrimp (Lysmata amboinensis) do not live in anemone, but will set up shop on live rock or coral outcroppings and wait for fish or eels to come and be cleaned of parasites or dead tissue. A popular shrimp with aquarists, Lysmata amboinensis is also known as the Scarlet Skunk Cleaner Shrimp or the Red Skunk Cleaner Shrimp because of the distinct pair of bright red stripes that outline the single white stripe running down its back. The Shrimp is often found in groups. They range is size from three-quarters to two inches.
Sun Anemone shrimp (Periclimenes rathbunae) can be seen in the Caribbean, Bahamas and Florida, but they are much less common in Bonaire than the other shrimp described here, perhaps because their host anemone is not so common. They grow up to one inch and can be seen at depths ranging from three to 60 feet.
Banded Coral shrimp (Stenopus hispidus) is a shrimp-like decapod crustacean. Another common name is banded cleaner shrimp. It reaches a total length of 2.4 inches, and has striking coloration. The ground color is transparent, but the carapace, abdomen and the large third pereiopod are all banded red and white. The antennae and other pereiopods are white. The abdomen, carapace and third pereiopods are covered in spines.
Stenopus hispidus lives below the intertidal zone, at depth of up to 690 feet, on coral reefs, often hanging upside down. Like many other cleaners, it advertises to passing fish by slowly waving its long, white antennae. This shrimp uses its three pairs of claws to remove parasites, fungi and damaged tissue from the fish. Remarkably, researchers claim that Stenopus hispidus is monogamous.
There are many fascinating things to see in the waters of Bonaire. If/when you dive there, be sure to take your time (and maybe an inexpensive magnifying glass) and observe the tiny creatures, including the colorful shrimp.
Charles (Chuck) Shipley was a Professor of Computer Science until his retirement in 2005, when he and his wife Barbara moved aboard their 2001 Kadey-Krogen 48 North Sea Tusen Takk II. They have been cruising the Caribbean since January 2007.