Studies on Chironomidae in experimental recirculating stream systems. II. The growth, development and production of a spring generation of Orthocladius (Euorthodadius) calvus Pinder

Abstract

SUMMARY. Orthodadius (Euorthodadius) calvus Pinder. similar to Orthocladius (Euorthodadius) thienemanni Kieffer. colonized a new gravel substratum in two recirculating stream channels. A maximum population density of 68.621 m‐2 was attained after only 16 days. This had fallen to a negligible density by the thirty‐third day. Some recruitment occurred over most of the study period (April‐May 1981) and no single sharply defined cohort was evident. There was a large range of body lengths within each instar. and considerable overlap between instars. The population density estimates for instars I and II were low compared with instars III and IV. The relationship between instantaneous growth rate (g) and geometric mean length indicated that growth was best described by a Gompertz curve. Growth rate decreased with increasing length from a value of about 40% length day‐1 at 2 mm body length to about 5% length day‐1 at 9 mm. Growth rates for individual larvae, kept in culture, were very variable with maximum rates close to the values determined from the field data. Mean duration of larval life was 16 days. Estimates of production for the study period ranged from 13.5 g dry wt m‐2 (Channel III, size‐frequency method) to 34.2 g dry wt m‐2 (Channel II, Allen's graphical method, values corrected for non‐linear growth). Gut contents were estimated to represent about 55% of the total weight therefore production values should be reduced by this amount.