Diurnal Periodicity in the Drift of a Day‐Active Stream Invertebrate

Abstract

Diurnal periodicity in the drift of invertebrate was observed in Temple Fork (of the Logan River), a small Utah mountain stream in the summer of 1966. The larvae of a caddisfly, Oligophlebodes sigma Milne (Trichoptera: Limnephilidae) exhibited a marked day—active drift periodicity, a type rarely reported. Drift rates as high as 400 g (160,000 individuals) per 24 hr for the entire stream (discharge about 0.34 m3/sec) were recorded, with only 4% occurring during the night. Inflections in drift rate were not related to times of sunset or sunrise, as is the case with night—active species. Rather, a close positive correlation with water temperatures, normally higher during the daytime, was apparent. Such correlation suggests that, whereas light intensity is the phase—setting mechanism for night—active drift periodicities, in the present case of a day—active pattern, the phase—setting mechanism was water temperature.