An Unique Anchialine Pool in the Hawaiian Islands

Abstract

The Sailor's Hat crater was artificially formed on the south coast of Kaho'olawe Island in 1965 with explosives. The explosion formed a crater about 50 m from the shoreline, which penetrates the watertable to a 5 m depth. The pool at the bottom of the crater meets the criteria of an anchialine pond because it shows tidal fluctuation, has measurable salinity, and lacks surface connections to the sea. The water chemistry of this pool is similar to the ocean except silica is elevated and salinity is slightly depressed suggesting a small groundwater influence. The fauna is dominated by waterboatmen, an endemic shrimp and tubeworm, polychaetes, amphipods, an ostracod, gastropod, solitary ectoproct. anemone, flatworm and sponge. The atyid shrimp, Halocaridina rubra, is a characteristic species of Hawaiian anchialine systems and probably colonized this 32-year old pool by active migration via the watertable. Colonization by the remaining fauna may have occurred by storm surf (for marine species) or with the wind. Most predators are unable to inhabit anchialine ponds because of difficult access due to physical barriers, or to unsuitable ecological conditions. The anchialine habitat and life history strategy of the atyid shrimp have probably been important influences on the adaptative success of H. rubra in the Hawaiian Islands, and may be important characteristics of hypogeal anchialine species elsewhere.