ZoBell — 22 — Marine Microbiology 



limit the depth to which bacteria are found in bottom deposits because 

 many species thrive in the complete absence of free or dissolved oxygen. 

 Living anaerobic bacteria have been recovered from the greatest depths 

 sampled, namely about 25 feet (see Chapter VI). 



In general, neritic bottom deposits, or those in water adjacent to land 

 to the 200 meter depth contour, consist primarily of sand and other coarse 

 material. Oceanic bottoms, or those beyond the 200 meter line, consist 

 largely of muds and oozes. The oceanic or deep-sea deposits consist of 

 terrigenous or pelagic material. 



Terrigenous deposits come from the land or are formed close to land. 

 They consist of disintegrated rock fragments and the remains of certain 

 littoral organisms. Therefore the constituents may be classified as either 

 inorganic or organic. Terrigenous deposits are also classified according to 

 texture which is a function of their content of sand, silt, or clay. The 

 International Society of Soil Science gives the following mean dimensions 

 for sand, silt, and clay: 



Terrigenous deposits can be characterized according to color which may 

 be black, white, blue, red, yellow, green, or brown. 



Pelagic deposits consist of the remains of calcareous and siliceous 

 organisms from the overlying water and the hydrous silicates of iron and 

 aluminum from the disintegration of materials from submarine volcanic 

 action. 



If the sediment consists primarily of the tests of pelagic foraminifera, 

 it is termed globigerina ooze. In coccolith oo7e the calcareous remains of 

 Coccolithophoridae, minute flagellates, predominate. Pteropod ooze is 

 characterized by a predominance of the calcareous shells of pteropods, 

 small gastropod mollusks. Diatom ooze and radiolarian ooze contain a 

 large proportion of the siliceous skeletal material from diatoms or Radio- 

 laria respectively. Pelagic deposits which contain less than 30 per cent 

 of the calcareous or siliceous remains of organisms are known as red clay. 



For further information on the properties of marine bottom deposits 

 the reader is referred to Murray and Hjort (191 2), Teask (1939), and 

 SvERDRUP et al. (1942). 



Plant and animal population : — Over 8000 species of marine plants 

 have been described, with species of red algae, diatoms, brown algae, dino- 

 flagellates, green algae, and blue-green algae predominating in the order 

 listed. The red and brown algae, which are known collectively as sea- 

 weeds, are the most conspicuous plants along the coast and in shoal 

 waters, but it is the microscopic diatoms and dinoflagellates that are most 

 important in the economy of the sea. Diatoms and dinoflagellates are 

 more or less universally and generally abundantly distributed through- 

 out the photosynthetic zone. Though microscopic in size, their mass 

 greatly exceeds the combined mass of all other primary producers includ- 

 ing the more conspicuous seaweeds and higher plants. The siliceous 

 shells, or frustules, of diatoms are of considerable importance in sediments 



