Rapid growth rates of chironomids in three habitats of a subtropical blackwater river and their implications for P : B ratios

Abstract

Growth rates of chironomids from communities characteristic of three major stream habitats were examined at a field laboratory on the 6th‐order Ogeechee River in the lower Coastal Plain of Georgia. Artificial systems that simulated environmental conditions of snags, sand, and backwater habitats were used to compare growth rates of members from these different communities. Three or more growth trials were run in each system for between 9 and 16 d. The average daily biomass growth rate for individuals across all trials was highest in the snag community (0.50 d−1) followed by the backwater (0.25 d−1) and sand (0.16 d−1). The low rate in sand was attributed primarily to psammophilous taxa, Lopescladius sp. and Rheosmittia sp. For taxa found in more than one habitat, we did not find significant differences in growth among habitats. Taxon‐specific growth rates were linearly and negatively related with the natural logarithm of mass for Corynoneura taris and groups of related taxa within the Tanytarsini and Polypedilum spp. Size‐specific growth rates were applied to quantitative field data from summer 1982 to calculate daily productivity of selected chironomids from the sand habitat. Daily biomass turnover (P : B g) ranged from 0.13 to 0.51. The mean growth rate for selected sand taxa (0.31) translates into a 6‐month P : B ratio (with temperatures >20°C) of ~57. With the exception of the psammophilous taxa, annual P : B ratios for most taxa in all three habitats approach or exceed 100.