Composition and abundance of periphyton and aquatic insects in Sierra Nevada, California, stream

The species composition of periphyton and benthic insect communities and abundances of common taxa (&;gt;0.1&;#37; of individuals) were examined during snow-free months in Convict Creek, a permanent snowmelt- and spring-fed stream in the Sierra Nevada of California. The communities were highly diverse. The most abundant taxa in the periphyton were diatoms ( Achnanthes minutissima, Cocconeis placentula lineata, Cymbella microcephala, C. sinuata, Fragilaria construens, F. crotonensis , Navicula spp., Synedra acus , and S. rumpens ), except in late spring and summer when several seasonal blue-green algae ( Chamaesiphon incrustans, Lyngbya spp. and Oscillatoria spp.) are at their maximum densities. Most common periphyton taxa vary systematically in abundance with season, but relative abundances of taxa also appear to be influenced by streambed scouring and by concentrations of ambient nutrients. Data on population densities and length frequencies of larval and nymphal stages of common benthic insects and occurrences of pupal and adult stages were examined to determine life history patterns. Taxa hatching in winter and spring and abundant as immatures in late spring include ephemeropterans ( Epeorus longimanus, Drunella flavilinea , and Caudatella heterocaudata ), plecopterans ( Calineuria californica, Doroneuria baumanni, and Pteronarcys princeps ) and dipterans ( Cryptolabis sp.). Common taxa hatching in late spring or summer are the plecopteran Malenka ( californica? ) and the trichopterans Arctopsyche grandis and Rhyacophila acropedes . Several bivoltine and multivoltine ephemeropterans ( Baetis devinctus and B. tricaudatus ) and dipterans ( Simulium spp. and Chironomidae) have summer cohorts. Taxa hatching in late summer or autumn and most abundant in autumn include ephemeropterans ( Baetis spp., Ephemerella infrequens, Epeorus dulciana, Ironodes lepidus , and Paraleptophlebia pallipes ), trichopterans ( Hydropsyche oslari, Lepidostoma spp., Glossosoma califica, Micrasema sp., Brachycentrus americanus, Neophylax sp., and Rhyacophila vaccua ) and dipterans ( Antocha monticola, Pericoma sp., and Chironomidae). Major recurring events that may influence life history patterns and structure of the benthic insect community are (1) near-freezing, nighttime winter water temperatures and occasional anchor ice, (2) a prolonged period of high discharge in late spring and early summer (3) a brief summer, and (4) a prolonged period of moderate stream discharge in autumn when the substratum is stable and food is abundant.