Life cycle and production of Chironomidae (Diptera) from Lake Banyoles (NE Spain)

Abstract

SUMMARY1. The life cycles and annual production of the eight most abundant species of chironomids (Prodadius cf. choreus, Tanypus punctipennis, Chironomus bernensis, Chironomus gr. plumosus, Cladopelma virescens, Microchironomus tencr, Tanytarsus gr. lestagei, and Cladotanytarsus atridorsum) were studied from sublittoral and profundal samples taken monthly in Lake Banyoles during 1987 at five sampling stations (depths ranging from 5 to 20 m).2. The number of generations per year deduced from instar‐frequency data varied from one to four, depending on the species, lake basin and depth. Annual temperature range, dissolved oxygen in the stratified period and presence of sulphide are the key factors that may explain the differences in the number of generations.3. Production estimates were calculated using the size‐frequency (SF) method corrected for the number of generations (SFG), and the increment‐summation method (IS) when cohorts could be clearly deduced.4. Production calculated with the SFG method gave results which were comparable with those of the IS method using smoothed‐survivorship curves in the three species for which the use of the IS method was possible (C. virescens, M. tener and C. atridorsum). Using these methods production was estimated to range from 23–70 mg AFDW (ash‐free dry weight) m−2 yr−1 at 12 m to 74–275 mg AFDW m−2 yr−1 in the sublittoral zone of the lake (5‐m depth).5. Calculation of production for the other five species using the size‐frequency method with the number of generations (SFG) deduced from monthly instar‐frequency data gave values ranging from 12 mg AFDW m−2 yr−1 (Chironomus bernensis at 20 m depth) to 3.75 g AFDW m−2 yr−1(Prodadius cf. choreus at 12 m).6. Total chironomid production (with the SFG method) varied from 0.8 to 5 g AFDW m−2 yr−1 in the profundal and sublittoral, respectively. At each sampling station two species groups accounted for most of the production: Prodadius cf. choreus and Chironomus spp. Annual production/biomass ratio (P/B) varied from very high values for Prodadius (between 11 and 27, as four generations completed each year) to very low values for Chironomus gr. plumosus (2.20), which completed only one generation each year. The annual production of P. cf. choreus in Lake Banyoles is higher than any reported in the literature due to the completion of four generations and to the high densities of this species.