RIPARIAN BEETLES (COLEOPTERA) ALONG A SMALL STREAM IN THE OREGON COAST RANGE AND THEIR INTERACTIONS WITH THE AQUATIC ENVIRONMENT

The purpose of this study was to determine density and composition of riparian arthropod communities and food habits of predacious riparian beetles along a 3rd order stream in the Oregon Coast Range. The surfac e dwelling riparian invertebrate community along the stream is mainly composed of ground beetles (Carabidae; 29.8%). rove beetles (Staphylin idae; 21.2%), water scavenger beetles (Hydrophilidae; 19.5%), and spid ers (Araneae; 5.0%). Carnivorous organisms comprise 41.8% of the epige ic fauna, detritivorous organisms 34%. The remaining 24.2% could not s afely be classified as either carnivorous or detritivorous. Twenty-fiv e carabid, 6 dytiscid, and 10 hydrophilid species were present. Eleven carabid species were exclusively found on sand bars. All abundant car abid species are spring breeders. Gut content analyses for three carab id and one dytiscid species were carried out (n=304). Chironomid (Dipt era) larvae comprise approximately one third of the prey of the gravel bar dwelling ground beetles Bembidion osculans Casey and B. kuprianov ii Mannerheim. They also feed on other small Diptera larvae, aquatic o rganisms such as caddisfly larvae, and emerging adult Diptera. More th an 70% of the prey of the sand bar dwelling Omophron ovale Horn and of Hydrotrupes palpalis Sharp were chironomid larvae. The riparian preda tors tend to be largely dependent on aquatic organisms and on species living in the aquatic-terrestrial interface.