An energy-flow model for a typical littoral zone would be similar to that in 

 figure 7-5, except that (1) attached plants would dominate the producer level 

 (phytoplankton would be present, also); (2) a much larger proportion of the 

 net primary productivity (mostly macrophytes and attached algae) would be 

 invested in detritus food chains on the bottom; (3) inputs of allochthonous 

 organic detritus would be greater; (4) the biomass of detritus-feeding 

 invertebrates (and associated predators) would be greater than that in the 

 pelagial zone. 



Food Webs 



A general food web for the pelagial plankton community of a Maine lake is 

 given in figure 7-7. The generic examples given in the web are known to occur 

 commonly in Maine lakes (Davis et al. 1978a and Cowing and Scott 1975, 1976, 

 and 1977). Feeding relationships among the plankton have not been studied in 

 Maine lakes. The base of the web consists of phytoplankton and allochthonous 

 organic matter, which are fed upon by herbivorous (and detritus-feeding) 

 zooplankton and heterotrophic bacteria. The herbivorous zooplankton are fed 

 upon by the predatory zooplankton and planktivorous fishes. Many organisms 

 occupy more than one trophic (feeding) level. The zooplankton that feed on 

 detritus may ingest autochthonous as well as allochthonous detritus and the 

 bacteria and fungi associated with both types of detritus. That is, a portion 

 of detritus is recycled within the pelagial plankton food web itself. The 

 remainder of the detritus is carried out by the outlet stream or falls to the 

 bottom where it becomes the food for a benthic food web (not included in 

 figure 7-7). In the profundal zone the web includes various detritivorous and 

 deposit-feeding chironomids (e.g., Chironomous) , tubificid oligochaetes (e.g., 

 Limnodrilus ) , and the fingernail clam Pisidium , the predatory chironomids 

 (e.g., Procladius ) , and the predatory phantom midge Chaoborus (Davis et al. 

 1978a). Detailed information on the pelagial biota of 17 Maine lakes is given 

 by Davis and coworkers (1978a). Cowing and Scott give information for 43 

 other Maine lakes (1975, 1976, 1977, and in preparation ) . 



The littoral zone food web (figure 7-8) is much more complex than the pelagial 

 plankton food web. No thorough descriptions have been done of the littoral 

 parts of lake systems in Maine. Davis and coworkers (1978a) and Cowing and 

 Scott (1975, 1976, 1977, and in preparation ) sampled the plankton and 

 macrozoobenthos in the deepest parts of Maine lakes whose entire areas were 

 littoral. Cowing and Scott (1975, 1976, and 1977) surveyed the common 

 vascular plants in 43 Maine lakes, four of which (Brewer, Branch, Green, and 

 Highland) are in the coastal zone. The base of the web consists of 

 macrophytes and other producers. 



Algal epiphytes on vascular plants may account for a significant portion of 

 littoral productivity (Wetzel 1975). Food for subsequent parts of the 

 littoral web includes allochthonous organic matter, as well as organic matter 

 produced in the littoral zone itself. The consumer populations (herbivores 

 and carnivores) are dominated by many different kinds of arthropods 

 (especially insects and crustaceans) and fishes. The heterotrophic bacteria 

 and fungi occupy a central position in the littoral food web in that feces, 

 dead organisms, and dissolved organic matter from various sources ultimately 

 serve as a food source for these decomposers, which, in turn, may be ingested 

 by consumers. 



7-29 



10-80 



