GULF OF MEXICO 



219 



litorature on this subject has boon annotatod by 

 ZoBoU (1946a). Seaweeds, diatoms, dinoHagjol- 

 iates, ami otlier marine plants may be extonsivoly 

 parasitized by pathogenic bacteria, actinomyces, 

 yeasts, and mold fungi. The wasting disease of 

 eelgrass, which threatened the extermination of 

 Zostera marina along the Atlantic seacoast a few 

 years ago, is believed to be due to infection by 

 Labyrinthula species (Renn 1936), although Halo- 

 pMoboluii species ma}- also be involved (Barghoorn 

 and Linder, 1944). 



By vitiating the water in local environments or 

 in the wake of periods of intense organic produc- 

 tivity, bacteria may have far-reaching adverse 

 effects on the plant and animal populations. 

 Among the ways m which bacteria contribute to 

 the vitiation of aquatic environments are by de- 

 pleting dissolved oxygen, by producing hydrogen 

 sulfide, by forming toxic amines, or bj' changing 

 the pH of the water. So-called stagnant water 

 basins are rendered uninhabitable primarily by 

 the activities of bacteria, and extensive areas in 

 the open ocean may become temporarily lethal 

 for plants or animals. For example, Copenhagen 

 (1934) described an area approximatelj' 25 by 200 

 miles in the Atlantic Ocean off Walvis Bay, South 

 Africa, where hydrogen sulfide is liberated period- 

 ically by bacterial activity in quantities sufficient 

 to kill both flora and fauna. The bacterial vitia- 

 tion of water is believed by the writer to be an 

 important feature of the "red tide." Extensive 

 populations of purple sulfur bacteria, observed by 

 Gietzen (1931) growing associated with decom- 

 posing algae along the Holstein coast, imparted a 

 distinctly red coloration to the sea. 



Marine bacteria also contribute to the bio- 

 fouling of man-made structures. The attach- 

 ment and growth of barnacles, bryozoans, tuni- 

 cates, mussels, clams, algae, and other fouling 

 organisms on ships' bottoms or other submerged 

 surfaces may be pi-omoted by bacteria in various 

 waj-s (ZoBell and Allen 1935). Likewise, micro- 

 organisms may contribute cither directly or in- 

 directl}^ to the deterioration of pilings, planks, and 

 other wooden structures in sea water. Lines, 

 ropes, nets, semes, sailcloth, and other cordage 

 or textile products readily rot in sea water unless 

 they are treated to preserve them from microbial 

 decomposition (Atkins and Warren 1941). Un- 

 protected steel and iron structures are also sus- 



ceptible to attack by bacteria which oxidize fer- 

 rous iron, produce acids, form hydrogen sulfide, 

 create reducing conditions, or depolarize hydro- 

 gen films resulting from the reaction between 

 water and iron. Acid production in microspheres 

 from the bacterial oxidation of organic matter or 

 sulfur may result in the corrosion of concrete. 

 Even rubber and bituminous coating materials 

 may be attacked by marine micro-organisms 

 (ZoBell 1950a). 



Bacteria are important chemical and geological 

 agents in marine bottom deposits where they 

 promote many processes involving organic com- 

 pounds, inorganic constituents, and physicochem- 

 ical conditions that affect the modification or 

 diagenesis of sediments. One of the first geo- 

 chemical processes to be studied by microbiologists 

 was calcium carbonate precipitation which Drew 

 (1911a, b) attributed to the activities of denitri- 

 fying bacteria found in great abundance in shallow 

 subtropical seas in the vicinity of Jamaica and 

 Tortugas. He (1912) reported that marine mud 

 near the Bahamas contained an average of 160 

 million bacteria per ml. with Bacilliis calcis pre- 

 dominating. Working in the same region, Keller- 

 man and Smith (1914) confirmed Drew's hypoth- 

 esis on the precipitation of calcium carbonate by 

 bacteria which raise the pH by reducing nitrate, 

 by producing ammonia, or by utilizing organic 

 acids. 



After finding rather sparse bacterial populations 

 in the open sea around Tortugas, Lipman (1929) 

 questioned whether bacteria contribute signifi- 

 cantly to calcium carbonate precipitation. This 

 view was rendered untenable, however, by the 

 extensive observations in the Bahamas of Baven- 

 damm (1932) who concluded that calcium carbon- 

 ate precipitation in tropical seas is primarily a 

 microbiological process. Similar conclusions were 

 reached by Gee (1932) who investigated bacterial 

 activity in the Florida Keys. Micro-organisms 

 found there by Gee and Feltham (1932) promoted 

 the precipitation of calcium carbonate by produc- 

 ing ammonia and otherwise increasing the pH. 



The pH of marine sediments may be increased 

 by micro-organisms which (1) form ammonia, (2) 

 reduce nitrate or nitrite, (3) reduce sulfate, (4) 

 oxidize or decarboxylate organic acids, or (5) 

 utilize CO2. On the other hand, the (1) produc- 

 tion of CO2 or organic acids, (2) oxidation of 



