Infodoc : Sciences, Techniques et Culture

The ecology of Hydrocyphon (Coleoptera: Scirtidae [= Helodidae]) was investigated in Tai Po Kau Forest Stream (TPKFS), New Territories, Hong Kong, over a two-year period. Quantitative benthic samples were taken from different microhabitats within a single riffle reach of the stream on 47 occasions, and were used as a basis for investigating life-history patterns and estimating secondary production. Hydrocyphon showed rather asynchronous growth, sporadic occurrence of adults and almost continuous recruitment, but interpretation of size-frequency histograms indicated that four generations were produced in each year. Annual production of Hydrocyphon (in terms of ash-free dry weight, AFDW) in the study reach over the period 1977-79 was 44.29 mg AFDW 0.5 m-2, but was 47% higher in 1977-78 [...]

The ecology of Hydrocyphon (Coleoptera: Scirtidae [= Helodidae]) was investigated in Tai Po Kau Forest Stream (TPKFS), New Territories, Hong Kong, over a two-year period. Quantitative benthic samples were taken from different microhabitats within a single riffle reach of the stream on 47 occasions, and were used as a basis for investigating life-history patterns and estimating secondary production. Hydrocyphon showed rather asynchronous growth, sporadic occurrence of adults and almost continuous recruitment, but interpretation of size-frequency histograms indicated that four generations were produced in each year. Annual production of Hydrocyphon (in terms of ash-free dry weight, AFDW) in the study reach over the period 1977-79 was 44.29 mg AFDW 0.5 m-2, but was 47% higher in 1977-78 (53.47 mg AFDW 0.5 m-2) than in 1978-79 (36.28 mg AFDW 0.5 m-2). These values lie within the range of production estimates made previously for psephenid beetles in TPKFS. Production: biomass ratios for Hydrocyphon were relatively stable and varied between 11.45 and 12.61 over the two years of the study. Densities of Hydrocyphon larvae in the study reach averaged 76.6 ± 25.5 individuals 0.5 m-2 (± 95% CL) over the study period, but mean densities were 56 % higher in 1977-78 than 1978-79. The were no obvious seasonal trends in larval density. Despite considerable within-patch variation, there was a clear pattern of abundance among patches on the stream bed: population densities were significantly lower close to the stream banks and larvae were more abundant in midstream. Stepwise multiple regression using algae, detritus and sediment statistics (mean grain size, sorting, skewness and kurtosis) as independent variables (i.e. 'predictors' of abundance) indicated that Hydrocyphon population densities were inversely related to the quantities of detritus in microhabitat patches, but the proportion of variation in scirtid abundance accounted for by detritus was low.