Chapter XVII 



ECONOMIC IMPORTANCE OF MARINE 

 MICROORGANISMS 



Marine microorganisms are of economic importance in many ways 

 besides causing diseases and bringing about the decomposition of marine 

 animals and commercial algae. Their indirect effects upon the primary 

 productivity of the sea and their possible role in the origin of oil have 

 already been mentioned. A few additional ways in which bacteria and 

 allied microorganisms are of direct economic concern to man are outlined 

 on the following pages. 



Fouling of submerged surfaces : — In nautical parlance fouling is the 

 attachment and growth of a heterogeneous assemblage of plant and animal 

 organisms on ships' bottoms, piles, water conduits, and other submerged 

 structures. Virtually all types of structural materials, whether they be of 

 wood, metal, concrete, glass, or plastic, sooner or later become fouled 

 when submerged in the biotic zone. The assorted organisms are popularly 

 known as "barnacles," "shells," "seaweeds," or "moss." While barnacles 

 or algae are usually the principal offenders, not infrequently a hundred or 

 more different species of organisms have been identified in fouled surfaces, 

 exclusive of bacteria and allied microorganisms. Sometimes nearly a 

 hundred tons of fouling organisms are found on the bottom of a large ves- 

 sel after it has been in the water for a year. Several pounds of fouling or- 

 ganisms may accumulate on the bottom of a flying boat within a few days. 



By increasing the resistance of ships in water, fouling organisms dimin- 

 ish the speed of a vessel, prolong the voyage, increase fuel consumption, 

 and augment wear and tear on the machinery. Fouling organisms necessi- 

 tate the drydocking of vessels at frequent intervals for cleaning, scraping, 

 and re-painting, costly processes which take the average vessel out of 

 commission for three or four weeks each year. The fouling problem is of 

 gravest concern to the Navy, particularly when operating far from home 

 bases. 



Microorganisms are the primary film formers on submerged surfaces. 

 On badly fouled surfaces bacteria may constitute as much as 8 or 9 per 

 cent by volume of the total cumulation. Bacterial attachment to previ- 

 ously cleaned glass surfaces may be detected in less than an hour following 

 immersion in the sea. The numbers increase more or less geometrically 

 with time until their abundance, together with the simultaneous attach- 

 ment and growth of diatoms, algae, protozoans, suctorians, and various 

 larvae, defeats census attempts. This may be illustrated by data sunmia- 

 rized in Table XLI on page 194. 



Laboratory as well as field observations (ZoBell and Allen, 1935) 

 suggest that bacteria may play an important role in the fouling of sub- 

 merged surfaces. This they may do in a variety of ways: (/) By affording 

 the planktonic larval stages of fouling organisms a foothold or otherwise 

 mechanically facilitating their attachment. (2) By discoloring glazed or 

 bright surfaces. Visscher (1927) and others have shown that bright, 



