Chapter XV 



MICROORGANISMS IN MARINE AIR 



One of the first problems investigated by pioneer marine microbiolo- 

 gists on oceanographic expeditions was the bacterial content of the atmos- 

 phere. Prior to the observations of Certes (1884a), Fischer (1886), and 

 MiNERViNi (1900), it was tacitly assumed that the air over the ocean at 

 considerable distance from land was sterile. Dating from their investiga- 

 tions, various kinds of microorganisms have been found in the air over the 

 ocean at all stations and elevations where samples have been taken. 



Bacteria in marine air: — While on the Talisman Expedition, Certes 

 (1884a) found bacteria in the air at considerable distances from shore. 

 However, they were present in such small numbers that he felt certain 

 that the aerial transportation of bacteria from land could not possibly 

 account for the presence of bacteria in the sea. 



Fischer (1886) made several hundred analyses of air over the ocean 

 between Kiel and Trinidad while crossing the Atlantic on the S.M.S. 

 Moltke. When the prevailing direction of the wind was onshore, terrige- 

 nous bacteria were rarely found in the air at distances exceeding 10 to 20 

 miles from land. Only small numbers were carried more than 70 to 120 

 miles from land by strong offshore winds. However, he admitted the pos- 

 sibility of bacteria being carried around the world with dust particles. He 

 stressed the cleansing action of precipitation. Corroborative evidence of 

 the paucity of bacteria in the air over the ocean has been recorded by 

 Levin (1899), Gazert (1902), Ekelof (1907), Pirie (191 2), and Hesse 

 (1914). 



Minervini (1900) found air-borne bacteria in all collections taken 

 over the Atlantic Ocean between Gibraltar and New York. Mold fungi 

 and pink yeast were also noted. Rain water collected at sea contained 

 small numbers of microorganisms. There were far fewer bacteria in 

 marine air than in air over the land. 



On various Pacific cruises of the Scripps, ZoBell and Mathews (1936) 

 found bacteria in the air over the ocean at all stations where tests were 

 made. In general, the abundance of bacteria decreased progressively with 

 distance from land. The numbers and kinds of microorganisms in the air 

 appeared to depend upon meteorological conditions. At land stations 

 terrigenous microorganisms predominated during offshore winds. During 

 prolonged onshore winds, marine microorganisms predominated. The 

 ability of the microorganisms to develop on fresh-water and sea-water 

 media was considered indicative of their origin. Illustrative data are 

 given in Table XXXVI on page 178. 



Besides their salinity requirements, other qualitative differences were 

 noted in the microbial content of marine and continental air masses. In 

 air masses known to have a marine history, Gram-negative, pigmented, 

 asporogenous rods generally predominate, with relatively few cocci. 

 Gazert (19066) and Hesse (1914) found virtually no cocci or spore-form- 

 ing bacteria in marine air. By contrast, large numbers of cocci and Gram- 



