Macrobenthos 



M. Butler, M. C. Miller, and S. Mozley 



INTRODUCTION TO ARCTIC BENTHOS * 



The larger benthic animals, which are mostly insects although snails 

 and worms do occur, are extremely important to the ecology of the ponds. 

 Not only are their biomass and productivity larger than those of any other 

 group of animals, but they also continually affect the structure of the 

 sediments by their feeding and burrowing. In one experiment, for example, 

 chironomids (at twice natural density) mixed and moved the sediments so 

 much that sand grains placed at the surface were completely covered in 10 

 days and 10% had reached a depth of 3 cm. This movement, plus the 

 circulation of water through their burrows, mixes oxygen into the 

 sediments and promotes the exchange of dissolved material. The benthic 

 animals also eat zooplankton, microfauna, benthic algae, and each other 

 and are, in turn, a food for insectivorous birds and even zooplankton. 



Macrobenthos of the ponds were investigated in two periods by 

 different investigators. In 1971 and 1972, D. M. Bierle collected extensive 

 data on distribution and dynamics, population densities, feeding, growth, 

 respiration, and production. Most data were collected in Pond J and on 

 larvae of the genus Chironomus, but comparative estimates of total 

 benthic secondary production were obtained for three other ponds, B, D, 

 and E. Unfortunately, the abundance of small forms and early larval 

 instars was underestimated and species were not adequately distinguished, 

 with the result that many population data represented mixtures of animals 

 with different life cycles. Some estimates were too low, such as larval 

 densities, spatial variance of larval populations, densities of emerging 

 adults, and length of larval lifespans, but estimates of larval and adult 

 biomass seem to have been too high. On the other hand, many data 

 collected in the earlier years on respiration, growth, larval feeding, trends 

 in directly measured total biomass, and occurrence of benthos or their 

 terrestrial life stages in bird guts were apparently valid. The present 

 authors collected further data on species composition, density, age 

 structure, emergence, and within- and between-pond variance in 1975, 

 1976, and 1977. A detailed description of these studies will be included in a 



*S. Mozley and M. Butler 



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