Macrobenthos 307 



brachyptery, shortened mid- and hind legs, and reduced antennal plume 

 separate it clearly from all other known Tanytarsus. It is a member of one 

 of at least four species pairs of Chironomidae in which one has normal 

 antennae and the other a reduced plume. In each case the reduced-plume 

 form cannot be identified in the literature and the two forms have 

 temporally distinct emergence periods. Oliver (1968) and Wiilker (1959) 

 have noted similar trends in other chironomids in extreme environments. 



In some cases, especially Metriocnemus, Psectrocladius and several 

 other Orthocladiinae, the species definitions and available keys are 

 inadequate. In others, Barrow pond forms are obviously new species, e.g., 

 Cladotanytarsus, Cricotopus and the aforementioned Tanytarsus. Other 

 species have type localities in Barrow: Trichotanypus alaskensis and 

 Derotanypus alaskensis. Barrow tundra ponds clearly have a fauna 

 distinct from that of previously studied areas. 



Emergence of Adults 



In 1975 adult midges were trapped in floating polyethylene pyramid 

 traps, each covering 0.1 m" of pond surface. In 1976 inverted funnel traps 

 were constructed of clear polycarbonate plastic. These funnel traps were in 

 contact with the bottom and enclosed 0.05 m" of sediment; this eliminated 

 problems of trap avoidance or attraction. Traps were cleared at 2- or 3-day 

 intervals from the earliest emergence (usually Trichotanypus in late June), 

 until mid-August when emergence of all species was virtually complete. 

 Both cast pupal skins and adults were collected. 



Comparisons of numbers of pupal skins with adults revealed that 

 floating traps introduced greater errors than bottom-resting traps. In 

 floating traps, the numbers of each fluctuated widely but sometimes skins 

 and other times adults were more numerous. In bottom-resting traps the 

 fluctuations were smaller and usually the number of adults exceeded 

 the number of pupal skins of each species. The greatest fluctuations in the 

 number of pupal skins occurred after the longest intervals between trap 

 clearing; therefore, skins are likely lost by sinking. Some adults were lost 

 or damaged by predators (probably mites, beetles, and perhaps 

 Heterocope) and by the act of clearing the traps; however, such losses were 

 greatly reduced in 1976 by the improved traps. 



All species had a single emergence each year in the ponds, and most, 

 especially the Tanytarsini and Trichotanypus, showed high synchrony 

 (Figure 7-5). Species emerging early in the season tended to show greater 

 synchrony than those emerging later. If the populations are synchronized 

 by thermal cues at or soon after the time of thaw as suggested by Danks 

 and Oliver (1972), then later emerging species would be expected to show 

 progressively decreasing synchrony. Another factor which may reduce 

 population synchrony is parasitism. During the 1976 emergence of 



