ZoBell — 174 — Marine Microbiology 



The experiments of Clarke and Gellis (1935) indicate that, while 

 bacteria may be important as food for copepods, there seem to be insuffi- 

 cient bacteria in the sea to provide for the complete nutritional require- 

 ments of "copepods. According to Waksman and Carey (19356), the bac- 

 terial population of the sea is kept down to a certain minimum due to the 

 consumption of bacteria by protozoans, copepods, and other marine ani- 

 mals, notably those of the mucous-feeding or filtering classes. 



Several kinds of zooplankton organisms were found by Voroschilova 

 and DiANOVA (1937) to ingest bacteria. These workers concluded that 

 bacteria nourish zooplankton organisms and that the predatory activities 

 of the latter tend thus to restrict the bacterial population of the Caspian 

 Sea. Pack (19 19) reported that ciliates in Great Salt Lake feed on bac- 

 teria. Baas Becking (1925) noted that sulfur bacteria appeared to be 

 the chief food of ciliates in sulfureta. 



Mud-dwelling detritus feeders studied by MacGinitie (1935) utilized 

 bacteria as food. Mare (1942) stressed the importance of bacteria as food 

 for bottom-dwelling animals in marine benthic communities. ZoBell 

 and Feltham (1942) estimated that around 10 grams (dry weight) of bac- 

 teria are produced per day per cubic foot of mud in a shallow marine mud 

 flat. The bacterial crop available for the nutrition of the animal popula- 

 tion in deeper colder bottoms of the open ocean, where less organic matter 

 reaches the sea floor, is cpnsiderably less than 10 grams per day. 



ZoBell and. Feltham (1938) demonstrated that the sea mussel, 

 Mytilus calif ornianus, ingests and digests bacteria. Specimens were main- 

 tained on an exclusive diet of bacteria for several months, during which 

 time the mussels, gained in size and weight". Few species of marine bac- 

 teria are injurious unless they are present in such great numbers that their 

 metabolic products vitiate the water. Bacteria were also found to sustain 

 the growth of the sand-crab, Emerita analoga, to a limited extent. Emerita 

 is more sensitive to large doses of bacteria than is the mussel and is less 

 efficient in removing bacteria from suspension. The Gephyrean worms, 

 Dendrostroma zostericola and Urechis caupo, were found to eat bacteria and 

 to derive nourishment therefrom. 



Baier (1935) listed several genera of rotifers, copepods, ciliates, and 

 flagellates which may feed directly upon bacteria and small nannoplankton 

 suspended in water. The larval stages of additional genera are planktonic 

 bacteria feeders. A second group of animals ingest bacteria along with 

 the mud and slime which they swallow promiscuously, digesting the usable 

 portion and ejecting inert materials. Nematodes, mussels, tube worms, 

 and the larvae of midges are in this category. A third group of bacteria 

 feeders discussed by Baier are animals which graze on solid objects like 

 rocks, aquatic plants, and suspended solids of various kinds. Certain 

 snails, ostracods, copepods, and amoebae are mentioned as examples of 

 animals which feed in this manner. Concerning the latter group, Baier 

 writes that it is not the decomposing plant substance but rather the bac- 

 teria, the cause of the decomposition, which nourish the grazing animals. 



That bacteria are ingested and digested by highly diverse fauna is 

 incontrovertible, but quantitative data on their relative importance in the 

 food cycles in the sea are wanting. It is doubtful if bacteria are suf- 

 ficiently abundant in sea water to constitute an appreciable item in the 

 diet of marine animals, but cumulatively bacteria must play an important 

 role in food cycles by synthesizing cell substances and by converting 

 waste or dissolved organic matter into a particulate form which can be 



