Marine Life 



Several types of marine organisms attacl< various materials used in 

 underwater power transmission systems. The need for information and data 

 on the resistance of materials to attack by marine organisms is therefore 

 important. There is considerable published information on the suitability of 

 natural organic materials, such as wood, jute, and hemp, for marine use. Some 

 data are now becoming available on plastics, elastomers, casting resins, and 

 similar materials. 



The highest concentration of marine life is found in intertidal regions 

 and down to 600 feet, depending on the penetration of sunlight. Beyond 

 600 feet, to a depth of approximately 4,000 feet, an abundance of animal life 

 can be found, but plant life is rare. At depths exceeding 4,000 feet, the water 

 temperature approaches freezing, food is scarce and, therefore, marine life is 

 rare. Marine life in this zone consists mainly of borers, such as worms, mollusks, 

 gastropods, hydroids, and sea urchins. 



Marine borers are mollusks or crustaceans which bore into a material 

 for food or shelter. Of the crustaceans, the gribble (Limnoria lignorum) is the 

 most destructive to cellulose materials. Most borers are found in shallow 

 depths; however, some boring mollusks have been found down to 1 1,500 feet. 

 Records show that the lead sheath of submarine cables were penetrated by 

 borers at depths of 5,600 feet. 



A group of marine organisms attach themselves to exposed surfaces, 

 resulting in what is commonly termed "fouling." Associated with the fouling 

 organisms is a microscopic anaerobic bacteria which, because of its sulfate- 

 reducing character, is predominant in accelerating corrosion and destroying 

 nonmetallic materials. The bacteria are generally single cell organisms, a large 

 number of which are heterotrophic, that attack organic matter and use the 

 carbon as a source of energy. The bacteria play an important role in the 

 biology of the sea and are found in seawater and sediments from shallow 

 depths to the deepest areas of the ocean. Submarine cables, mooring lines, 

 and other power structures are particularly susceptible to deterioration by 

 bacteria since bacteria are most plentiful in seawater as well as in the first 

 few inches of bottom sediment. 



Summary 



An all-encompassing definition of surface conditions of the world's 

 major oceans is difficult due to the large variations in weather conditions, 

 thermodynamics, and prevailing winds which determine the characteristics of 



