New photos are providing scientists with their best look yet at the rare, secretive shrimp that inhabit Hawai'i's subterranean anchialine pools.

The photos by Department of Land and Natural Resources staff were taken on Maui and at the state's 'Anuenue Fisheries Research Center on Sand Island.

"These images are some of the first of their kind for Hawaiian anchialine pool shrimp and open a window into the life history and behavior of the species," said aquatic biologist Mike Yamamoto, who took some of the photos.

Anchialine pools are found along coastal lava flows. Although land-locked, these brackish pools have an underground connection to the ocean and are subject to tidal fluctuations.

There are more than 650 anchialine pools in Hawai'i, with approximately 90 percent of them on the Big Island. However, very few of these pools are inhabited by shrimp.

Yamamoto said most anchialine pool shrimp occupy an extensive network of water-filled cracks and crevices that lead to and from the actual pool. This makes it difficult for researchers to obtain accurate population estimates. In most cases, scientists are able to only note the presence or absence of a species in the habitat being surveyed.

Loss of shrimp species from suitable habitat is the best method to date of measuring a decline in species, according to DLNR aquatic biologists.

Six species of anchialine pool shrimp were photographed by Yamamoto, Matt Ramsey and Tom Iwai: Metabetaeus lohena, Procaris hawaiana, Palaemonella burnsi, Callaismata pholidota, Antecaridina lauensis and Halocaridina rubra.

The first three species are candidates for endangered or threatened status under the Endangered Species Act.

Halocaridina rubra, known in Hawaiian as 'opae'ula, is the only one of the six with a common name. It is the most common species of anchialine shrimp in Hawai'i and can reach 10 to 15 years of age, an unusually long time for a tiny crustacean.

Depending on the species, anchialine pool shrimp range from two-tenths of an inch to about 1 1/4 inches in length and come in a variety of colors, including brilliant red, pale pink, white, light yellow, grayish-green, transparent and banded.

The three major threats to anchialine pool shrimp are habitat destruction and degradation, non-native invasive species and overcollection for the aquarium trade.

The Department of Land and Natural Resources and the U.S. Fish and Wildlife Service are partners in a cooperative effort to conserve and monitor anchialine pool shrimp and their habitats throughout the state.

Ramsey, a DLNR resource ranger, advises people visiting anchialine pools to only observe and not touch, and not to bring trash or other native or non-native aquatic animals or plants into the pools.

And before buying 'opae'ula, Ramsey said to make sure the vendor has the proper permits to sell them.