Abstract

Stream animals on tropical high islands have ecological counterparts among continental fauna but are confronted with highly dynamic and variable environmental conditions that can far exceed those occurring in mainland streams. In response to weather fronts passing through an island chain or to localized fluctuations in the formation of orographie rain, water levels in island streams can change from low flows of a few centimeters depth to sudden flash floods of several meters and back to clear shallow water within a few days. Studies of the five species of indigenous Hawaiian stream fishes have shown that the dispersal of larvae out to sea and their return several months later during their amphidromons life cycles constantly restock streams and provide a kind of ready reserve for recolonizing streams after unusually harsh disturhances, such as the recent Hurricane Iniki. Because of the predominance of amphidromy among the major species of stream fishes and macroinvertebrates on tropical Pacific high islands, we hypothesize that maintaining biodiversity in these island streams when conditions are otherwise favorable and restoring animal life to formerly diverted streams may be no more complicated than assuring that the freshwater-marine threshold remains open and that natural fluctuations in flow are unhampered.