performed using ^^C in field conditions as well as in basic laboratories, 

 showed that natural bacterioplankton can serve as a normal source of 

 nutrition for infusoria, sponges, hydroids, coral polyps, Appendicularia , 

 planktonic crustaceans (Cladocera, copepods, euphausiids), bivalves and 

 gastropods, filtering polychaetes (sabellids, and serpulids), holothurians, 

 ascidians (Sorokin, 1966, 1971b, 1972, 1973a, d,e; Sorokin et al., 1970; 

 Pavlova, Sorokin, 1970; Pavlova et al . , 1971; Petipa et al . , 1971, 1974; 

 Ponomareva et al., 1971). Figure 18 presents the results of determination 

 of the comparative intensity of nutrition of a number of filter feeders by 

 phytoplankton and bacterioplankton. 



For the fine filter feeders (sponges, Appendicularia , Cladocera, 

 Polychaeta, veligers, mollusks], bacterioplankton at concentrations close 

 to the natural ones (0.2-1 g/nr wet biomass) can fully satisfy their 

 nutrient needs. For many of these species, they are an even more important 

 source of nutrition than the phytoplankton. The coarse filter feeders 

 (copepods, euphausiids, bivalve mollusks, ascidians) are unable to filter 

 out the dispersed bacterial cells and consume primarily the aggregated 

 portion of the bacterioplankton. They, therefore, use bacterioplankton 

 less effectively than phytoplankton of the same concentration (Fig. 19). 

 Nevertheless, for them also, the microbial biomass is an important reserve 

 of additional food. In experiments involving determination of the 

 intensity of consumption of labeled bacterioplankton by coarse filter 

 feeders (Copepoda), with the same concentration of unlabeled phytoplankton 



SC 





i 



'/ I 





a 



■// 



\ Va 







Acartia 



i 



Fig. 18. Daily rations (R, % body weight) of massive spei,ies of plankters 

 and their nutrition by bacterioplankton (a) and phytoplankton (b). Fine 

 filter feeders ( Oikopleura , Penilia ), the veligers ( Serpulorbis ), medium 

 filter feeders ( Paracalanus ) , coarse filter feeders ( Eucalanu sT, and 

 predators (Acartia). ~~ 



present, and vice versa (Petipa et al . , 1974), it was shown that the 

 bacterioplankton represented 30-50% of their diet (Fig. 20). Even such 

 predacious crustaceans as Euchaeta marina frequently consume 

 bacterioplankton. 



278 



