Macrobenthos 299 



Most species lists of arctic or cold-subarctic insects are based on 

 collections of adults and do not discriminate among terrestrial, semi- 

 terrestrial and truly aquatic forms (Watson et al. 1966b; McAlpine 1965; 

 Rickard and Harmston 1972). The benthic studies of Holmquist (1973) 

 have focused on coastal lakes and the presence or absence of marine relicts 

 among the macrobenthos. 



The Char Lake IBP study emphasized dynamics, production, and 

 controls on macrobenthos, particularly Chironomidae (Welch 1973, 1976, 

 Welch and Kalff 1974, Lasenby and Langford 1972). Chironomids shared 

 dominance with Mysis relicta in Char Lake but there were few species; 

 Orthocladiinae were dominant and the variable ice cover occasionally 

 interfered with annual reproduction. Char Lake conditions represented a 

 more extreme polar environment than those in Barrow. Secondary 

 productivity in Char Lake was extremely low because of low primary 

 productivity (Welch 1976). It was also found that chironomids have longer 

 lifespans in the Arctic than in temperate latitudes, two or three years in the 

 Char Lake species. 



Barrow thaw ponds contrast with other investigated arctic habitats in 

 several ways. The species of Chironomidae are somewhat different from 

 those in other areas, although genera are similar. Some of the statements 

 and suppositions of Livingstone et al. (1958) about the absence of dytiscid 

 beetles and widespread dominance of Corynocera in the Arctic are not 

 borne out. Lifespans of benthic animals are longer than earlier authors 

 report, and growth is slow in terms of calendar years. However, 

 development is rapid in view of the low summer temperatures and when 

 compared with daily rates at lower latitudes. A sum of less than 1 year of 

 ice-free days is required for maturation in all the smaller species. 



Species Composition 



The principal organisms were collected from core samples of 

 sediments as well as by sweeps of emergent vegetation, by submerged 

 pitfalls, by quantitative entrapment of emerging adult insects, and by some 

 aerial netting. The list (Table 7-1) is remarkable in several ways. Virtually 

 every taxon contains fewer species than would be expected in a temperate 

 pond and many taxa are missing altogether. There are no Ephemeroptera, 

 Odonata, Hemiptera or Megaloptera, no Hirudinea, lumbriculid or naidid 

 Oligochaeta, no Pelecypoda, no Amphipoda, Isopoda, or Decapoda. 

 Mosquitoes are absent in contrast to their notorious abundances in thaw 

 ponds and pools farther inland. Indeed, there are few dipterans of any sort 

 besides the abundant and (comparatively) diverse Chironomidae. The 

 numbers of species of Coleoptera, Gastropoda, Trichoptera, and Acari are 

 all lower than in temperate waters. Even Chironomidae are not as rich in 

 species here as they are in permanent temperate ponds. 



