Influence of the Land Substrata 71 



bays and estuaries. After the eel grass was killed by a disease in the 

 early 1930's, large amounts of bottom material were washed away from 

 many sections of the shore. As the unprotected sand and mud was 

 scoured out by the tides, a great many other plants and animals that 

 had been living in the area were destroyed. Eventually the com- 

 plexion of the whole ecological community became altered (Stauffer, 

 1937). 



Another way in which organisms can modify the substratum is 

 through contributing their own remains. The sand on the famous 

 Pink Beach in Bermuda is composed chiefly of coral fragments. In 

 the deep sea some of the bottom oozes consist mainly of the skeletons 

 of planktonic organisms (Sverdrup, Johnson, and Fleming, 1942, Ch. 

 20). Glohigerina ooze formed by the accumulation of the shells of a 

 genus of Foraminifera and pteropod ooze similarly composed of the 

 shells of gastropods are examples of calcareous oozes ( Fig. 3.6 ) . Two 

 important types of siliceous deposits are formed by the accumulation 

 of the hard parts of radiolarians and diatoms, respectively. Radio- 

 larian ooze is found in certain tropical waters, and diatom ooze is 

 limited to colder seas. 



Aquatic organisms also act reciprocally on their own substratum 

 by adding organic material to it. In a peat bog the substratum is 

 practically 100 per cent organic matter resulting from the accumula- 

 tion of vegetable material (Welch, 1952, Ch. 16). In inland waters 

 and in the sea, fragments of dead organisms reach the bottom as an 

 organic detritus. Seaweeds and shore animals that have died and 

 been broken up by the waves contribute abundantly to this material, 

 but farther from shore the plant and animal plankton are largely re- 

 sponsible for the particulate organic material in the water. This 

 detritus tends to settle out where the current has been sufficiently 

 reduced. The excreta of worms, lamellibranchs, and various Crus- 

 tacea have been reported to form as much as 40 per cent of the fine 

 material in the mud of the Clyde Estuary. All these organic sub- 

 stances gradually become incorporated into the substratum and serve 

 as sources of nutriment for the mud-eating benthic animals (Twen- 

 hofel, 1939). 



ROCK, SAND, AND SOIL IN TERRESTRIAL ENVIRONMENT 



Influence of the Land Substrata 



In the land environment soil is by far the most important substratum, 

 but rock and special materials such as plants and plant products also 



