Sea horses enjoy eating native shrimp
While visiting a sea horse farm on the Big Island recently, I discovered a homemade pond on the premises. Bending to peer into the 5-foot-deep hollow blasted from lava rock, I found what I expected: thousands of red, half-inch-long opae ula, Hawaii's native anchialine shrimp.
When the aqua-farmers dug this hole, a mixture of fresh and salt water seeped up through lava cracks, creating a pond. As expected, the shrimp then rose from their natural underground home, feasted on algae and multiplied like mad.
Later in our tour, we visitors were invited to feed some of these shrimp to the sea horses. I poured my jar of water containing several opae ula into the tank and watched the sea horses inhale them. Is this OK? I wondered. It felt so wrong.
Hawaii hosts eight species of anchialine shrimp. All are red, all live in anchialine (brackish seaside) pools and all survive underground.
Our most common anchialine shrimp, found only in Hawaii, is opae ula, (Halocaridina rubra), the only one with a common name. These are the little red shrimp people buy in sealed glass jars.
The second species of Halocaridina, called palahemo, lives in only one pool on the Big Island. Biologists haven't seen any there in recent surveys, but that doesn't prove they're extinct. Some could be thriving in deep, underground cracks.
Of the six other species of anchialine shrimp that live in Hawaii, the following four are endemic:
» Metabetaeus lohena (1 inch long) eats opae ula. This shrimp was once found in pools on Oahu, Maui and Hawaii but is now rare on all three islands.
» Palaemonella burnsi (quarter-inch) lives in three Maui ponds inside state reserves, and one Big Island pond.
» Procaris Hawaiiana (1 inch) is found in two Maui ponds and one on the Big Island.
» Vetericaris chaceorum (2 inches) has been seen in only one Big Island pond, a lava tube 131 feet deep and 984 feet long.
The two remaining shrimp species in Hawaii are also found in other parts of the world.
Antecaridina lauensis (half-inch) lives in two pools in Maui and two on the Big Island. It is also found in anchialine pools of Fiji, Mozambique, Saudi Arabia and Japan.
Our other international shrimp, Calliasmata pholidota, is a blind snapping shrimp seen in seven pools on Maui and the Big Island. This species also lives in Tuvalu on Funafuti Atoll and in the south of Egypt's Sinai Peninsula.
No one knows how these two shrimp species got far so apart. One theory is that in ancient geological history these shrimp were oceanic, and the formation of continents separated them.
Researchers also theorize that anchialine ponds might not be essential to these shrimps' survival, that their true home is underground. If so, that's good news, because humans have destroyed 90 percent of Hawaii's anchialine ponds.
Opae ula are not on the endangered species list, nor is anyone petitioning the U.S. Fish and Wildlife Service to add them. That, plus the fact that the sea horse farm shrimp exist only because the farmers dug a hole, and that the farm's tour guides teach visitors about our opae ula, leads me to this conclusion: It's OK to let visitors feed farmed opae ula to farmed sea horses. It is memorable wildlife experiences like this that make us care.