Seasonal dynamics of invertebrate drift in a Hong Kong stream

Abstract

In Tai Po Kau Forest Stream, mean drift density was 277.9 ± 25.0 individuals 100 m-3; peaks in density were apparent during autumn and spring. Some 102 taxa were recovered from the drift; total number of taxa was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67.3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40.4% of individuals caught. Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature: Simulium T1 (Diptera), Anisocentropus maculatus (Trichoptera) and Amphinemura chui (Plecoptera) drifted most in winter, whereas Chimarra T1, Polymorphanisus astictus (Trichoptera), Helodes sp l and cf. Rhantus sp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring (Indobaetis sp., Cinygmina T1, Serratella T2), autumn (Baetiella sp., Pseudocloeon T2), or spring and autumn (Baetis nr pseudofrequentus) peaks which were not clearly related to water temperature. In only A. maculatus and P. astictus was drift seasonality associated with life-cycle events. Overall, there was no evidence of community-level trends in the periodicity of stream drift in this seasonal tropical habitat. -from Author