LARVAL HABITAT PREFERENCE OF THE ENDEMIC HAWAIIAN MIDGE, TELMATOGETONTORRENTICOLA TERRY (TELMATOGETONINAE)

Telmatogeton torrenticola Terry is a large endemic chironomid (last in star >20 mm) commonly found in high gradient Hawaiian streams on smoot h rock surfaces with torrential, shallow flow and in the splash zones of waterfalls. We have quantified benthic water how in larval habitat in a 50 m segment of Kinihapai Stream, Maul using a thermistor-based m icrocurrent meter. Under base flow conditions at sites suitable for la rval attachment, depth was measured and bottom water velocity measurem ents were made approximate to 2 mm above populations. Larval densities ranged from 386.9-1178 m(-2) habitat bottom water velocities from 13. 4-64.2 cm s(-1), and water depths from 1.5-50 cm. Bottom velocities of sites with zero larvae ranged from 20.8-21.8 cm s(-1) with depths fro m approximate to 50 to >160 cm. Larval densities were greatest in area s with high bottom water velocities and shallow depths. Stepwise multi ple regression analyses showed that density could be confidently predi cted best by Froude number (r = 0.81; p = 0.008). In the absence of Fr oude number as a regression term, the best variable to predict larval density was bottom velocity ratio: relative depth ratio (r = 0.75; p = 0.019). In addition, the torrential habitat of the larvae was always characterized by a periphyton community that appeared to be the primar y food resource for the larvae. These data suggest that torrential flo ws over appropriate substrates are important factors regulating habita t availability for ?: torrenticola and that reduced discharge (e.g. af fected by water diversions) could significantly reduce the amount of a vailable habitat for this organism and other flow sensitive stream fau na.