Major Findings 15 



Metazoans which are found in arctic ponds do not appear to have any 

 particular adaptations to arctic conditions because the same forms are 

 often found in temperate ponds as well. Rather, many of the adaptations 

 or abilities they already possess that permit them to survive freezing or 

 other stresses permit survival in the Arctic as well. For example, in 

 temperate lakes, cladoceran zooplankton overwinter as diapausing eggs or 

 embryos and the cyclopoid copepods overwinter as diapausing subadults 

 (copepodids); the same species has a copepodid diapause stage in 

 temperate lakes where it moves into the sediment for several months. They 

 utilize the same methods for longer periods in the Arctic. 



Many of the arctic forms of midges have adults which have reduced 

 wings. After hatching, the adults move about on the water surface rather 

 than make the typical laying swarms. This behavior keeps them from 

 being blown away by the constant winds. The life histories of many higher 

 animals are affected by the low temperatures. Zooplankton grow so slowly 

 that there is time for but a single generation per year in most species. This 

 puts a very specific upper limit on annual production of zooplankton 

 because the number surviving the winter may be the single most important 

 factor determining annual production. Chironomids, which live in the top 

 several centimeters of sediment where the annual average temperature in 

 the summertime is only about 3°C, are most affected by the environment. 

 They grow very slowly; one species of Chironomus takes 7 years to pass 

 through the four instar stages. In spite of these difficult conditions for 

 growth, the number of midge species found in the ponds, around 35, is not 

 very different from the number in a temperate pond. Many of these species 

 have been found only in the Arctic or only in the Barrow area. 



The sedge, Carex aquatilis, that grows in the pond is well adapted to a 

 variety of habitats from dry meadows to the shallow water. Perhaps the 

 most obvious adaptation to the arctic environment is its ability to begin 

 growth when the air temperature is still close to 0°C. It also takes up 

 phosphorus through the roots at these very low temperatures. 



Modeling 



A part of the original plan of the U.S. IBP was to construct predictive 

 mathematical models of various ecosystems. This pond study offered 

 several advantages for this approach; the ecosystem is somewhat 

 simplified and physical factors (circulation and stratification) could be 

 ignored; the active life of the pond organisms is completed in only 100 days 

 each year; all the investigators worked on a common pond; controlled 

 experiments could be carried out in replicate ponds and in the nearby 

 laboratory. Our conclusion is that modeling is a very helpful approach but 

 that the construction of a large, complicated predictive model is not 

 possible with the existing gaps in our knowledge of aquatic ecology. 



