Wednesday, April 16, 2008

A sextet of Hawaiian anchialine shrimps

In the oddest, often most inhospitable habitats of the islands—deep in the most remote lava tubes and in tiny pools on fields of sun-baked rock—there is native Hawaiian life.

The native shrimps of Hawai'i's anchialine ponds are fascinating examples.

(Photos: Top: Kanehena achialine pool on Maui. Middle: Red and white color morphs of the 'ōpae 'ula, or Halocaridina rubra, heading in opposite directions. Bottom: The shrimp Procaris hawaiana. All phones by Mike Yamamoto, used with permission.)

The U.S. Fish and Wildlife Service and the state Department of Land and Natural Resources Division of Aquatic Resources released photos of six species of Hawai'i's anchialine shrimps.

Anchialine ponds, where the shrimps live, are generally coastal ponds with no surface connection to the sea, but which rise and fall with the tides, suggesting some underground connection. They can range in salinity from nearly as salty as the ocean to quite fresh, with the fresh water often flowing from the mountains toward the sea.

Often the water is layered, with the freshest water lying near the surface and saltier water below.

“Three of the six species of anchialine pool shrimp are candidates for listing as endangered or threatened under the Endangered Species Act,” said Lorena Wada, candidate conservation coordinator for the Fish and Wildlife Service for the Pacific islands. The three, listed below, are the Metabetaeus, the Procaris and the Palaemonella.

Hawaiian anchialine shrimps tend to be found in clean water in either lava coastlines or limestone areas with open sinkholes. Much of the time, the shrimps appear to remain in cracks and underground water-filled caverns that are not accessible to humans, and so they are hard to count and to study.

The best known of the six Hawaiian anchialine 'ōpae is the 'ōpae 'ula, of which eight distinct genetic lineages have been located—indicating that once these creatures take up residence in a new part of the island, they tend to be isolated there and evolve into unique forms.

The 'ōpae 'ula are found on Maui, Hawai'i and O'ahu.

They grow to about a half-inch in length and are by far the best-known of the tiny achialine 'ōpae, but hardly the only ones.

The Palaemonella burnsi is much smaller—in the range of a quarter-inch—and is mainly found in only the saltiest pools—three known polls on Maui and one on Hawai'i.

Procaris hawaiana, shown here, is pinkish in color and can grow to more than an inch long. It is found in two clusters of pools on Maui and one on Hawai'i.

Metabetaeus lohena can be pale pink to bright red, is about three-quarters of in inch long at maturity, and can prey on its cousin, 'ōpae 'ula. Its numbers appear to have been declining, but it is found on the same three islands as 'ōpae 'ula.

A plant-eater, Antecaridina lauensis is about half an inch long and reddish, and tends to be active at night. It is found in two groups of pools each on Maui and Hawai'i.

And Callaismata pholidota, from half an inch to more than an inch long, is pink to red with red bands. It's a predator and scavenger. It is apparently not common, and is found from a few pools on the Big Island and on Maui.

Learn more about the anchialine shrimps at a previous post here:

A Hawai'i state status report on eight shrimps is here:

A fact sheet on six species, with images, is here:

© 2008 Jan W. TenBruggencate