416 S. F. MacLean, Jr. 



TABLE 11-2 Composition of the Mite (Acari) Fauna in the Coastal 

 Tundra at Barrow 



compared with temperate forest and grassland ecosystems. 



Density of Collembola varied between 24,400 individuals m"- in the 

 basins of low-centered polygons and over 150,000 m"^ in the polygon 

 troughs and moist meadows, and was greater than that of mites in all 

 nine microtopographic units sampled, although the difference was small 

 in the three drier units. Collembolan density showed no relationship with 

 soil moisture. 



Biomass of Collembola was not determined directly. Population bio- 

 mass was estimated using a standard value of 4 ^g per individual, taken 

 from Petersen's (1975) observations of adult Folsomia quadrioculata 

 and from Fjellberg's (1975) observations of F. diplophthahna in arctic- 

 alpine Norway. These two species made up 70% of the total collembolan 

 density in our samples (MacLean et al. 1977). Using this value, estimated 

 biomass of Collembola exceeded 0.5 gdw m"^ in the most favorable 

 areas. 



The Diptera strongly dominated the numbers, biomass, and diver- 

 sity of tundra macroarthropods (Table 11-3). Three cranefly species 

 (Tipulidae) are particularly prominent: Prionocera gracilistyla, a large 

 species with larvae in the wettest habitats; Tipula carinifrons, a large spe- 

 cies of mesic and dry areas; and Pedicia hannai, a smaller species with 

 carnivorous larvae that are most abundant in wet meadows and the 

 polygon troughs. Larvae of other species of lower Diptera (Nematocera), 

 including especially midges (Chironomidae) and fungus gnats (Myceto- 

 philidae and Sciaridae), were recorded at densities of up to 685 individu- 

 als m"^ This must be considered a minimum estimate due to uncertain- 

 ties of samphng and extraction efficiency (Healey and Russell-Smith 

 1970). A large proportion of the smaller larvae may have been over- 

 looked, which would lead to a serious underestimate of density, but not 

 of biomass. 



Rotifers, which are more commonly associated with freshwater hab- 

 itats, occurred in all microtopographic units, with a mean annual density 

 in the wettest meadows of 40,000 ind m"-. Tardigrades occurred at densi- 



tl 



