III-E-2 



Darnell, R.M. 1961. Trophic spectrum of an estuarine community, based 

 on studies of Lake Pontchartrain, Louisiana. Ecology 42:553-568. 



One of the fundamental questions in aquatic ecology is the problem 

 of community nutrition. Several recent investigators have achieved 

 a high degree of success in working out Quantitative aspects of primary 

 production in natural aquatic communities. However, studies of the 

 problems of secondary production have not yielded results of the same 

 consequence. This has been due to the absence of good quantitative 

 methods of analyzing consumer nutrition and to the comple^xity of the 

 nutritional relations among the consumer species. With a few notable 

 exceptions, comprehensive data regarding the nutrition of a large 

 share of the consumers of a given aquatic community have not been 

 available, and overall patterns of the trophic relationships among 

 consumer species have not been well understood. As a part of a study 

 conducted in Lake Pontchartrain, 1953-55, food habitats of 35 of the 

 most important consumer species were investigated to achieve a more 

 thorough understanding of the problem of consumer nutrition and its 

 relationship to primary production in a complex natural community. 

 The results of the food studies of the various species have been 

 published, and the present work is an attempt to interpret these 

 results in the context of the total coninunity. 



Principal findings are summarized as follows: 



1. The Lake Pontchartrain community is a broadly open system, 

 exchanging nutrients, producers, and consumers with adjacent fresh- 

 water and saltwater areas, as well as with neighboring marshes and swamps. 



2. Consumers within the lake apparently depend in great measure 

 upon primary production which takes place outside the lake. Hence, 

 the estuarine community may be trophically unbalanced. 



3. The most conspicuous single food item in the diets of the 

 consumers of this community is organic detritus with its attendant 

 bacteria. 



4. Individual species do not appear to conform to specific trophic 

 levels because of the following considerations: 



a. Most, if not all, of the major consumer species are ominivorous. 



b. Consumers select food opportunistically. 



c. Ontogenetic changes occur in the food habitats of the consumers. 



d. Organic detritus is important in the nutrition of the consumer 

 species, some being largely dependent on it. 



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