26 ANAEROBIC HABITATS 



vertebrates and their rcspiratoi-y habits is unfortunately 

 too fragmentary to allow one to make definite state- 

 ments concerning- the biological importance of the oxy- 

 gen-free bottom layers in the open sea. The wide dis- 

 tribution of anaerobic bacteria in the bottom material of 

 the deep seas (Waksman, 1934; ZoBell and Anderson, 

 1936) is an indication that anaerobic conditions are per- 

 haps a general feature of the bottom of all major oceans. 



It is of interest to note that similar conditions occur 

 near or on the seashore and it is especially significant 

 that ZoBell and Feltham (1942) encountered several 

 species of worms and other burrowing animals as deep 

 as 40 cm., and still deeper in a mud flat, that is, at a 

 depth at which there was no free oxygen and where the 

 Eh was around - 0.2 volts. Severe oxygen deficiencies 

 or complete lack of oxygen have been found in the water 

 permeating the sand of sandy beaches. Such cases have 

 been described in Denmark by Thamdrup (1935) and 

 in North Carolina by Pearse, Huntm and Wharton ( 1942). 

 Further investigations of similar localities would be 

 promising in view of the rich burrowing fauna occurring 

 on the sea shore. 



Fleming and Revelle (1939), in discussing dissolved 

 oxygen in the ocean, state: "The free dissolved oxygen 

 content of the interstitial water in the sediments and 

 immediately above the bottom will have a profound in- 

 fluence upon the conditions in the sediments and will 

 also affect the bottom fauna. Where there is little or 

 no oxygen, there can be little or no life other than bac- 

 teria. " In view of the facts that will be presented in 

 this monograph, such a generalization can hardly be 

 understood. 



B. Bulk of ivater basins. In many fresh water lakes 

 periodic annual stagnation of the lower water masses 

 occurs. This is primarily caused by a thermal strati- 

 fication which effectively prevents an exchange between 

 the water masses separated by the so-called thermocline. 



