The ʻōpaeʻula (Halocaridina rubra), also known as the Hawaiian red shrimp or volcano shrimp, is a small shrimp from the Atyidae family.
Small in size, about 1.5 centimeters (3/5 inch), it feeds on algae, plankton, bacteria and diatoms. ‘Ōpae’ula can carry about 12 fertilized eggs under their abdomen for a hatching period of roughly 38 days. Reproduction occurs once or twice a year, and the shrimp can live up to 20 years.
The ʻōpaeʻula is an endemic species that occupies alkaline brackish water lakes near the sea coast. Its habitat is unique and restricted to five islands in the Hawaiian archipelago: Maui, Kahoʻolawe, Oʻahu, Molokaʻi and Hawaiʻi. On the island of Maui, specimens are found in the brackish water of Muliwai, where the freshwater stream meets the sea, but they have also been found in karst caves on older islands such as Oʻahu.
They shrimp have a sweet taste and are eaten whole with their head and shell, either raw or boiled.
According to an ancient legend, a Hawaiian princess named Popoalaea escaped from her cruel husband, Chief Kakae, and hid inside the cave of Waianapanapa. A faithful maid accompanied her and, one day, as she sat in front of the princess, she waved a kahili feather, a symbol of royalty, in the air. Noticing the reflection of the kahili feather in the water, Chief Kakae discovered Popoalaea’s hiding place and killed her. At certain times of the year, small red ʻōpaeʻula shrimps appear in the brackish pond of the cave, coloring the water red. Legend has it that this is a reminder of the blood of the slain princess.
The introduction of non-native species into the pools near the sea is now a major threat to ‘ōpae’ula: Species such as tilapia and guppies prey on them voraciously. Habitat loss is also a major threat, as is the aquarium trade.