WATER MANAGEMENT FOR MARINE AQUARIUMS 



and Lackey (1956) determined that pas- 

 sage through the filters at Marine Studios 

 (Marineland) generally removed more 

 than half of the circuhxting bacteria. 

 Herald et al. (1962) found that exposure 

 to ultraviolet reduced demonstrable bac- 

 terial populations of 1,200 to 2,000 per cc. 

 to practically zero. Marshall and Orr 

 (1958) successfully used Chloromycetin 

 and streptomycin to prevent the bacterial 

 multiplication that occurs when fresh sea 

 water is put into aquariums, but there were 

 indications that antibiotics may sometimes 

 harm invertebrates exposed to them. 



The importance of microorganisms, es- 

 pecially bacteria, to the state of the water 

 in marine aquariums can scarcely be over- 

 emphasized, and not until we have a better 

 understanding of bacterial activities can 

 we hope to develop a truly rational tech- 

 nique of taking care of it. The funda- 

 mental difference between the behavior of 

 small standing fresh-water aquariums and 



those containing sea water lies with their 

 microbiology. The real "balance" of the 

 former consists in the relatively stable 

 condition of its microbial population, even 

 in the presence of quite large amounts of 

 organic material. The basis for this phe- 

 nomenon is not definitely known. Breder 

 (1931) has suggested that it may be partly 

 the development of buffering capacity by 

 the water and the appearance of bacterio- 

 phage, while studies of Dr. Seymour 

 Hutner have indicated that the develop- 

 ment of a dominant population of preda- 

 tory protozoans is largely responsible. 

 The situation in fresh water may well be 

 exceptional, but the reasons for its absence 

 in sea water would nevertheless be of in- 

 terest. For example, bacteriophages have 

 been found in the ocean (Spencer, 1960), 

 but they do not seem to have been looked 

 for in marine aquariums or other artificial 

 environments. 



CHANGES OCCURRING IN SEA WATER AFTER LONG USE 



The outstanding changes occurring in 

 sea water that has been kept in circulatory 

 systems for months or years are two: a 

 permanent lowering of the pH and an 

 accumulation of nitrates. After 20 years 

 of use, an analysis of the sea water in the 

 New York Aquarium revealed that the ni- 

 trate content had increased more than 250- 

 fold and that the pH had dropped below 

 neutrality (Townsend, 1928). Similar 

 data, involving similar or shorter periods 

 of time, have been reported for the Lon- 

 don Aquarium (Stowell, 1926a; Brown, 

 1929; Oliver, 1957), the Amsterdam 

 Aquarium (Honig, 1934; Sunier, 1951), 

 and the Ueno Aquarium (Saeki, 1958). 



In nature, the pH of sea water seldom 

 exceeds 8.4 or drops below 7.5 (Sverdrup, 

 Johnson, and Fleming, 1942). It is regu- 

 lated by a series of chemical equilibria in- 

 volving carbon dioxide, carbonic acid. 



sodium bicarbonate, and sodium carbonate 

 which forms a buffer mechanism and 

 makes possible the addition of relatively 

 large amounts of acid or alkali before the 

 pH is appreciably altered (Harvey, 1928, 

 1955). If enough acid is added, all the 

 excess base (alkali reserve) will be de- 

 stroyed, but this occurs at a pH of 5.5, a 

 far stronger acidity than the vast major- 

 ity of marine fishes and invertebrates can 

 endure. There has been disagreement as 

 to the exact source of the acidity brought 

 about by the metabolism of fish, in addi- 

 tion to that caused by the carbon dioxide 

 they produce, but it is agreed that oxida- 

 tion is the ultimate fate of practically all 

 the excretions of fish — which is, of course, 

 an acid-producing process. 



Three methods of maintaining the pH 

 in marine circulations have been used. At 

 the Plymouth Aquarium, freshly slaked 



