Macrobenthos 



301 



TABLET! (Continued) 



Metriocnemini 



Corynoneura spp. (several) 

 Metriocnemus spp. 



(at least 2) 

 Pseudosmittia gr. sp. 

 Parakiefferiella gracillima 

 P. nigra 



Limnophyes sp. 

 Lapposmittia sp. 

 Mesosmittia sp. 

 Bryophaenocladius sp. 



Individual species of animals tend to occur primarily either in the soft 

 sediments in pond centers or among stems and leaves of Carex and 

 Arctophila around the edge. These two habitats and the animals 

 associated with them are represented in Figures 7-1 and 7-2. In the centers, 

 Chironomidae, led by Chironomus sp., Tanytarsini spp., and Procladius, 

 make up 75 to 95% of the biomass while Oligochaeta contribute almost all 

 the remainder (Figure 7-3). Tubificidae account for most worm abundance 

 but the rarely encountered Enchytraeidae are very large forms and may be 

 locally important. At the edges among plants, other insects and the snail 

 Physa account for much of the biomass since their weight per individual is 

 high. 



Distribution of chironomid species between macrophytes and pond 

 centers is best illustrated by data from emergence traps (Figure 7-4). 

 Tnchotanypus and most Orthocladiinae were associated with the Carex 

 plants. Emergence of Corynoneura into all traps probably reflects 

 redistribution of active prepupae or pupae, as benthic samples showed 

 larvae of this species to be restricted to the vegetated pond margins. Other 

 subfamilies had species-specific habitat preferences, with clear distinctions 

 seen even within genera. Chironomus pilicornis, Procladius vesus, and 

 Tanytarsus inaequalis were all most abundant in pond center traps, while 

 C. riparius, P. prolongatus, and T. gregarius gr. sp. 2 occurred equally or 

 predominately in "Carex" traps. 



Most macrobenthos in the ponds are detritivores and most of these 

 are deposit feeders. As noted, however, .most species we found were 

 chironomids; the trophic structure of these will be considered later in the 

 chapter. The remaining macrobenthos species have a variety of feeding 

 mechanisms. 



All the Oligochaeta at Barrow are deposit feeders that always feed 

 below the surface. Nemoura and Tipula may be shredders or gatherers of 

 fine detritus among the macrophytes. Micrasema probably feeds on living 

 plants (Wiggins 1977) while Asynarchus, another caddis fly, is omnivorous 

 and even feeds on Turbellaria, dead Nemoura, and other Asynarchus. The 

 dytiscid beetles are predators both as adults and as larvae. The mite 



