A Diel Comparison of the Unique Faunal Assemblage in Remote Anchialine Pools on Hawai‘i Island

Anchialine pools, which are defined as land-locked mixohaline pools with tidal influence, are unique and increasingly rare habitats in the Hawaiian Islands. Particularly, anchialine pools in Manukā on the island of Hawai‘i are home to a diverse, rare, and unique assemblage of decapod crustaceans. Diurnal and nocturnal surveys of motile aquatic species were conducted across 81 anchialine habitats in the Manukā watershed to perform diel comparisons of species assemblages, richness, abundances, distributions, and hydrography. Nocturnal surveys revealed significant increases in abundances, distributions, and species richness throughout Manukā’s anchialine habitats. Of particular interest are six native anchialine decapods, Halocaridina rubra, Metabetaeus lohena, Calliasmata pholidota, Antecaridina lauensis, Procaris hawaiana, and Palaemonella burnsi, that exhibited notable diel patterns in abundance and distribution. In addition, a recent new record of a caridean shrimp and two unidentified species were documented. Factors influenced by diel period (i.e., behavior of introduced predators and sun exposure) and various hydrographic and habitat characteristics were suspected to affect patterns in the biological parameters that were measured. The addition of nocturnal surveys can provide valuable biological information to anchialine habitat resource management that would not have been obtained with diurnal surveys alone.