The duration and degi'ee of supersaturation de- 

 olined with each passing _year of the period studied. 



Strong annual variations in the degree of super- 

 saturation could very probably produce fluctua- 

 tions in the abundance and distribution of marine 

 organisms if these organisms can be aU'ected by 

 supersaturation. The most marked effect of super- 

 saturation on fish and other organisms is gas bubble 

 disease. This disease, liowever, does not appear un- 

 less certain conditions obtain. By convention, the 

 percentage saturation of dissolved gases in the sea 

 is the ratio between the observed concentration at 

 some depth and tlie concentration which would 

 exist at the sea surface in equilibrium with the 

 atmospliere at the same temperature and salinity 

 as the depth in question. Thus, water at moderate 

 depths may be supersaturated according to this 

 definition and yet because of the hydrostatic pres- 

 sure actually be capable of liolding much more 

 gas in solution. Ricker ( 1934) has called tlie degree 

 of saturation which is related not to a theoretical 

 surface value, but to the absolute capacity of water 

 at a given hydrostatic pressure, the "absolute satu- 

 ration." "Gas disease'" due to supersaturation alone 

 can occur only in absolute supersaturation. Fur- 

 thermore, this supersaturation must be extremely 

 high if gas disease is to be. caused by oxygen. Ob- 

 servations have been made of gas disease occurring 

 in the natural environment at oxygen saturations 

 of 250 percent (Renfro, 1963) and over 300 per- 

 cent (Woodbury, 1942). I have experimentally 

 induced gas disease in herring {Clupea h-arengus 

 harengu.?) at saturations of pure oxygen of 300 

 percent, but could not produce the symptoms at 

 less than 200 percent saturation. Nitrogen, how- 

 ever, seems to be dangerous to fish at saturations of 

 125 percent or more (Marsh and Gorham, 1905; 

 Egusa, 1959). In air-supersaturated water, I have 

 experimentally induced gas disease at saturations 

 of 120 percent nitrogen and 130 percent oxygen. 

 In my experiments, the lierring showed a definite 

 tendency to avoid the supersaturated water, but 

 only when the saturation levels were high enough 

 to produce gas disease. 



Gas disease can occur, furthermore, only when 

 tlie total gas pressure in tlie water exceeds the com- 

 bined hydrostatic and atmospheric pressures. When 

 the concentration of any gas is increased by the 

 displacement of another gas, gas disease is un- 

 likely as long as the total gas pressure is not in- 



creased. Fish have been exposed with little harm 

 to oxygen saturations of up to 400 percent by bub- 

 bling this gas into the water at atmospheric pres- 

 sure (Haempel, 1928; Bishai, 19C0). Pathological 

 symptoms occurred in some of Haempel's fish, but 

 tliey seemed to be unrelated to gas disease. 



The above evidence suggests very strongly that 

 tlie levels of gas supersaturation along the Maine 

 coast are not high enougli to have a direct detri- 

 mental efi'ect on fish in their natural environment. 

 Tlie situation under artificial conditions is much 

 different, however. In aquaria, lobster pounds, and 

 other similar installations where water is pumped 

 from below the surface of the sea into relatively 

 shallow tanks at sea level atmospheric pressure, 

 any nominal supersaturation becomes absolute. 

 This supersaturation, perhaps aggravated by ele- 

 vations in temperature or by the pumping system 

 itself could produce lethal conditions as it did in 

 our laboratory in the summer of 1964. The most 

 likely efi'ect of supersaturation on fish popula- 

 tions, if there is any effect at all, would probably 

 be indirect, but lack of evidence to demonstrate 

 such effects precludes useful discussion of them at 

 this time. The facts do show, however, that a con- 

 dition does exist, and recurs annually in more or 

 less cyclic fashion, which could conceivably play 

 a definite role in the ecology of marine organisms. 



LITERATURE CITED 



Bishai, H. M. 



1960. The effect of ga.s content of water on larval 

 and young fish. Z. Wiss. Zool., 163 : .37-64. 

 CoLTON, John B., Jr., Robert R. Marak, Samuel R. 

 NicKERSON, and Ruth R. Stoddard. 



1968. Physical, chemical, and biological ob.servations 

 on the continental shelf, Nova Scotia to Long 

 Island, 1964-66. U.S. Pish Wildl. Serv., Data Rep. 

 23, 19.'5 pp. on 3 microfiches. 

 Egusa, Syuzo. 



19.59. The ga.s disease of fish due to excess nitrogen. 

 J. Fac. Fi.sh Anim. Plusbandry, Hiro.shima Univ. 2: 

 157-182. 

 Gran, H. H., and Trygve Braarud. 



1935. A quantitative study of the phytoplaukton in 

 the Bay of Fundy and the Gulf of Maine (including 

 ob.servations on hydrography, chemistry and tur- 

 bidity). J. Biol. Board Can. 1 : 279-467. 

 (Jrekn, B. L. 



1965. A redetermination of the solubility of oxygen 

 In sea water and some thermodynamic implications 

 of the .solubility relationship.s. Ph.D. thesis, Massa- 

 chu.setts Institute of Technology, 137 pp. 



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