14 J. E. Hobbie 



course, a general slow-down of metabolism because of the cold 

 temperatures and this will affect all ecosystem processes from 

 decomposition to predation. Yet, low temperatures (2 to 8°C) are also 

 found in all temperate ponds; in fact, a majority of months will be cold- 

 water months. The unique properties of arctic ponds are: (1) they never 

 warm, (2) they are frozen for 8 1/2 or 9 months of the year, (3) there is 

 continuous light from late April until mid-August (although the intensity 

 does vary greatly over 24 hours). 



The smallest life forms of the ponds do not seem to have any special 

 adaptations to the Arctic. Bacteria, for example, are just as abundant in 

 the Arctic as in the water and sediments of any temperate pond; their 

 activity is low but it is about the same as for a temperate pond in the spring 

 when the water is cold. Phytoplankton species are almost identical to the 

 species found in temperate ponds in the spring. There is not even a 

 reduction of species number as 105 species were found in the ponds. These 

 same species, by the way, are found throughout the world and even reach 

 the Antarctic. The physiology of the algae was also normal except that at 

 low temperatures photosynthesis was strongly inhibited by high light 

 levels. This is not adaptive; it may be a result of the low temperatures 

 slowing the rate of repair of chlorophyll. It has been suggested that 

 photosynthesis is less affected than is respiration by low temperatures and 

 for this reason, biomass production would be very efficient in the Arctic. 

 We were not able to measure algal respiration or biomass changes very 

 well so we cannot say if this is true. 



Protozoans were also found to have the same species and total 

 abundance as temperate pond communities. Some forms that do not have 

 resistant resting stages might be absent, for so little is known of protozoan 

 life history that this could not be detected. Thus, it was surprising to find 

 Paramecium in the pond, for this species has never been known to form 

 resistant cysts. 



Mttazoans are affected in. a number of ways by the arctic 

 environment. The obvious way is by exclusion of some forms because of 

 physiological limitations. Amphibia and sponges are absent while 

 Hemiptera, Odonata and Megaloptera are rare. Ephemeroptera, 

 Trichoptera, and Coleoptera are represented by only a few families or 

 genera. 



Another way that organisms are affected is by exclusion from certain 

 habitats. For example, fish are found in deep lakes but not in ponds or 

 lakes shallower than 2 m; they are excluded by the 2-m-thick ice cover in 

 arctic fresh water. This absence of fish allows large zooplankton to exist 

 such as the large Daphnia middendorffiana which reaches 3 mm in length 

 and the fairyshrimp which can be 20 mm long. These large animals, in 

 turn, affect the species composition of the algae. We first noticed this 

 effect when all the zooplankton were killed in a pond by the addition of oil. 

 The same shift in the dominant algae, a replacement of the Rhodomonas 

 by Uroglena, also occurred when we removed the zooplankton by net. 



