the Oribatei, are by far the predominant group 
of Acarina. At Barrow, however, Douce (1973) 
reports that the prostigmatid mites comprised 
55% of the individuals and 16 of the 37 species 
found. Prudhoe Bay is even more extreme in the 
predominance of prostigmata; 79% of the mites 
on plots 1, 6, and 7 belonged to this group. This 
may be a general feature of tundra ecosystems: 
examination of data produced from other sites 
of the international Tundra Biome should allow 
resolution of this point. 
The total number of Collembola on all Prud- 
hoe Bay plots was lower than the Barrow mean. 
Thus, this system is not Collembola-dominated, 
as is the Barrow system. Differences in faunal 
composition occur within the Collembola. At 
Barrow the Entomobryidae comprise 90% of the 
total individuals; at Prudhoe Bay they comprise 
55% of the total. 
Sminthurid Collembola are rather uncom- 
mon at Barrow and somewhat more abundant at 
Prudhoe Bay, although they still do not form a 
numerically important part of the microfauna. 
Interestingly, they reach greatest abundance on 
wet plots at Barrow, but on the two dry plots at 
Prudhoe Bay. They are missing altogether from 
the polygon basin plot at Barrow, as they are 
from Prudhoe Bay plot 2. All of this suggests 
that there may be areas of wet tundra at Prud- 
hoe Bay not suffering from the “‘polygon basin 
syndrome,” in which sminthurid Collembola 
may reach even greater abundance. 
Biomass was not measured directly at Prud- 
hoe Bay. The numeric estimates of Table 3 were 
converted to biomass estimates using the mean 
dry weights per individual of 4 ug for Collem- 
bola, 5ug for Acarina, and 20 wg for Enchy- 
traeidae. The results are presented in Table 4. As 
at Barrow, the Enchytraeidae strongly dominate 
in all habitats sampled. Each of the Prudhoe Bay 
plots is well below the Barrow mean of 1,514 mg 
dry wt m2; however, Prudhoe Bay plot 6 corre- 
sponds precisely with the Barrow polygon basin 
which it otherwise resembles, and Prudhoe Bay 
plot 7, the Dryas-graminiform mesic heath, corre- 
sponds precisely with the Barrow raised polygon. 
Thus, when comparing similar habitats, the bio- 
mass of soil microivertebrates at Barrow and 
Prudhoe Bay is similar. However, the habitats 
sampled in this study represent a significant pro- 
portion of the Prudhoe Bay tundra, whereas com- 
119 
Table 4 
Estimated biomass of major invertebrate groups 
(mg dry wt m°2) at Prudhoe Bay, 29 August 1972. 
Plots 
Group Plofl) “Plot6) Plot 7 4/5 
Acarina 
Prostigmata 316 5 194 
Mesostigmata 5 O05 7219 
Cryptostigmata 60 29 20 
Total Acarina 381 35 233 
Collembola 
Entomobryidae 48 9 124 
Poduridae 15 2. 86 
Sminthuridae 14 0 31 
Total Collembola 77 11 241 
Enchytraeidae 636 1236 836 1316 
TOTAL 1094 1282 1310 
parable habitats at Barrow are limited in spatial 
extent. In other words, habitats low in inverte- 
brate biomass are the rule at Prudhoe Bay, but the 
exception at Barrow. As a whole, Prudhoe Bay 
tundra supports a lower biomass of soil inverte- 
brates than does Barrow tundra, in spite of the 
more temperate summer season climate and 
greater faunal and floral diversity found at Prud- 
hoe Bay. 
The depth distribution of microfauna (Table 
5) closely paralleled results found at Barrow. 
The majority of the fauna occurs close to the 
surface, which is most evident in the mites. All 
Table 5 
Depth distribution of soil microfauna (percent of 
total occurring in upper 2.5 cm of litter and soil). 
Plots 
Group Plot1 Plot6 Plot 7 4/5 
Acarina 
Prostigmata 93 30 93 
Mesostigmata 100 0 74 
Cryptostigmata 100 100 100 
Collembola 
Entomobryidae 83 100 87 
Poduridae 80 50 57 
Sminthuridae 100 82 
Enchytraeidae 87 87 61 82 
