Feeding, Reproduction, and Sense Organs of the Hawaiian Anchialine Shrimp Halocaridina rubra (Atyidae)

Abstract

The Hawaiian endemic shrimp Halocaridina ruhra Holthuis currently inhabits anchialine pools on Maui, Kaho'olawe, O'ahu, Moloka'i, and Hawai'i islands. Information is presented on the feeding, reproductive, and sensory biology of these shrimp. Feeding cheliped setae are of two types, serrated setae that scrape the substrate surface and filamentous setae that collect the loosened food materials or act as filters. The shrimp are primarily microphagous grazers that scrape the surface of the algal-cyanobacterial crust on pool substrates. This grazing activity is essential in maintaining the integrity of the crust, an actively growing matrix of plants, bacteria, diatoms, protozoans, and underlying siliceous and carbonate materials. Filter feeding is only observed in pools with dense phytoplankton blooms. The first and second pleopods of male and female shrimp are illustrated, and reproduction in captive populations from Hawai'i and O'ahu locations is described. Sense organs examined include the eye, aesthetasc hairs, campaniform sensilla, ringed setae, and abdominal pits with flared setae. The anchialine shrimp H. ruhra appears to be a generalist, feeds as a microphagous grazer or filter feeder, is well adapted to the epigeal-hypogeal habitat in the pools, reproduces in the subterranean portion of the habitat, and is equipped with sensory structures that detect motion and chemical changes in the environment. Survival of this endemic species is dependent upon the continued integrity of its habitat, which is unique and sparsely represented on five of the eight high Hawaiian Islands.