Harlequin Shrimp Discovery

Harlequin shrimp were first found in the Saipan Lagoon and reported to the CNMI’s Division of Fish and Wildlife (DFW) biologists in January 2004 by Captain Carl. Scientists had not previously recorded it anywhere in the Marianas Islands. This species of harlequin shrimp is named by scientists as Hymenocera picta and placed in the Family Gnathophyllidae. They are usually found in the eastern and central Pacific and reach a maximum size of less than 3 inches (8 cm). Their paddle-shaped legs and the distinctive pattern of strikingly beautiful spots on a white or cream background are used to positively identify the harlequin shrimp. This particular species tends to have yellow halos around the spots. The spots are believed to provide the shrimp with camouflage, because the spots blend in with the shadows and other patterns on the ocean bottom and coral reef. However, each individual has its own unique color pattern.

Harlequin shrimp are shy reef creatures and rarely seen. They tend to hide during the day in crevices and feed at night. Moreover, they tend to be uncommon even in the places they are found. Harlequin shrimp tend to mate for life and are usually found as a pair, with the female slightly larger than the male. Females also have blue or purple tips on the abdominal legs, whereas males have transparent abdominal legs. Harlequin shrimp are especially sensitive to copper and nitrates (often found in fertilizers and some detergents), both of which will kill the shrimp, even in very low concentrations.

Harlequin shrimp eat live starfish or sea stars. Biologists believe that the shrimp use their large antennae (on the head and with brownish spots and lines) to follow the scent or smell of the sea star. Once the pair of shrimp finds the sea star, they use their large paddle-like legs to push under the sea star and turn it over. The shrimp then eat the soft tube feet and other soft parts of the living sea star. Biologists also think that the shrimp may anesthetize the sea star (so that it doesn’t move away) and that the shrimp may even feed the sea star to keep it alive. The pair of shrimp may feed on a single sea star for over a month, before the sea star dies. Harlequin shrimp especially like to eat sea stars of the genus Linckia, including our common blue sea stars. In captivity, harlequin shrimp have also eaten crown-of-thorns sea stars and pincushion sea stars.

Pacific Islanders have harvested harlequin shrimp for food, but have carefully harvested only the largest pairs, and never many at the same time from the same location. Harlequin shrimp are also captured and sold as aquarium pets in some parts of the Pacific, but their diet can make them difficult to maintain as pets. They also tend to be too rare to capture consistently. Biologists in Hawaii have successfully bred and reared harlequin shrimp, so that wild populations do not have to be harmed by this industry. In the CNMI, people must apply for and receive an aquarium-collecting license from DFW before they attempt to capture these shrimp for display in aquaria. To export these shrimp from the CNMI, people must also get an export permit from DFW.

This “Fact Sheet” was produced by the CNMI Division of Fish and Wildlife and is available free of charge.