Abundance, population dynamics and production of Chironomidae (Diptera) in an ul traoligotrophic lake in South Greenland

Abstract

Macrozoobenthos of the ultraoligotrophic Lake 95 (61°N, 46°W, 8 ha, z_max=18 m,$\bar z = 6.9 m$) is composed of about 14 taxa dominated by 12 Chironomidae species. Abundance, life cycle, biomass and production were estimated for the six dominant taxa. Abundance declined fromca. 4150 at 2.5 m depth toca. 1400 ind m⁻² at 16 m depth and averagedca. 3200 ind m⁻² on a lakewide basis. By numbers,Heterotrissocladius changi andH. oliveri dominated the average fauna.H. changi was common at the 2.5 m and 5 m depth stations, whereasH. oliveri dominated from 5 m depth downwards. Chironomids showed mainly a 1-yr life cycle, but apparently bothHeterotrissocladius species had two contemporary cohorts with emergence in midsummer and late autumn/early spring, respectively. Average annual${P \mathord{\left/ {\vphantom {P {\bar B}}} \right. \kern-\nulldelimiterspace} {\bar B}}$ ratio was 4.2 and 4.6 forH. oliveri andH. changi, respectively. Annual production varied from 0.3 g ash-free dry weight (AFDW) m⁻² y⁻¹ at 16 m depth to 1.6 g AFDW m⁻² y⁻¹ at 2.5 m depthH. changi contributed 45%, fiveMicropsectra spp. 17% andH. oliveri 15% to total average production, which on a lakewide basis wasca. 1.1 g AFDW or 25 kJ m⁻² y⁻¹. Lake 95 thus belongs at the very low end of measured lake zoobenthic productions, which range from 10 kJ m⁻² y⁻¹ in Arctic lakes toca. 1600 kJ m⁻² y⁻¹ in highly eutrophic shallow lakes.