Decomposers, Bacteria, and Microbenthos 387 



after each peak of bacterial abundance. One group of ciliates fed on 

 bacteria and another group fed upon benthic algae. 



Nematodes were the most abundant metazoan at 1 to SxlO* m"^ 

 Rotifers were equally abundant but harpacticoid copepods reached 9x 10^ 

 m '"'. All of these animals had but one generation per year and all except 

 the copepods overwinter as eggs (copepods overwintered either as eggs or 

 asjuveniles). 



Most of the carbon flow in the microbenthos is through the 

 zooflagellates; ciliates and metazoans provide less than 10% of the total. 

 All of the microbenthic grazers remove about 28 Mg C m '^ day " ' or about 

 1 to 2% of the bacteria and algae. This is, however, about 20% of the 

 bacterial and 5% of the algal production each day. 



The microfauna are likely controlled in part by predation; most of 

 this is by other microfauna. This predation is difficult to quantify, 

 however. Predators do make up about 20% of the total ciliate fauna at 

 their peak abundance. Predation by macrofauna is likely only about 2% 

 day-'. 



Experiments with microcosms containing Carex, bacteria, and a 

 protozoan (Tetrahymena) showed both a decrease in bacterial numbers (2 

 to 3-fold) and an increase in bacterial activity when the protozoan was 

 present. This increase was not caused by any release of phosphate by the 

 protozoan. A direct measurement revealed that the ciliates contributed 

 only 4 to 5% of the total phosphorus excretion in the system. Actual 

 mineralization of phosphorus from the Carex was increased 40 times by 

 the presence of the grazer. 



Temperature seemed to have only a slight effect on the microfauna. 

 For example, in the middle of June only a few centimeters of sediment had 

 thawed out and the water was still at 2°C. Yet the protozoan fauna was 

 already fully developed. Later, the animals were able to reproduce and the 

 smallest forms had up to 80 generations during the summer. 



