WATER MANAGEMENT FOR MARINE AQUARIUMS 



vulcanite and ebonite, the use of which 

 was first recommended by Michael Fara- 

 day in 1857 (Lloyd, 1871). In recent 

 years, a number of plastics have also 



safe to use, however. In fact, if there is 

 any doubt about the suitability of a ma- 

 terial, it ought to be rigorously tested, by 

 the animals themselves, as recommended 



proved satisfactory. Not all plastics are and described by MacGinitie (1947). 



NATURAL CONSTITUENTS OF SEA WATER 



Overlying the differences between sea 

 water in nature and in confinement is the 

 basic similarity of its composition the 

 world over. The ratios between the nine 

 ions which constitute more than 99 per- 

 cent of its dissolved salts are virtually con- 

 stant (Sverdrup, Johnson, and Fleming, 

 1942; Harvey, 1955). This is a fortunate 

 circumstance that permits a great deal of 

 uniformity in approach and procedure by 

 aquarists and experimentalists as well as 

 oceanographers. On the other liand, at 

 least 52 elements have been found in nat- 

 ural sea water, and this complexity has led 

 to some irrational ideas about its chemical 

 composition, particularly in connection 

 with its duplication in the laboratory as 

 artificial sea water. A fundamental diffi- 

 culty is that conventional chemical nota- 

 tion cannot represent a mixture of many 

 anions, cations, and molecules, all in dy- 

 namic equilibrium. There is perhaps no 

 more striking illustration of this and its 

 relation to life in the sea than the obser- 

 vation that a volume of sea water allowed 

 to evaporate to dryness and then reconsti- 

 tuted with the proper amount of distilled 

 water will not support the variety of ma- 

 rine life it originally would. 



Moreover, as found in nature, sea water 

 is not only an inorganic complex. An 

 ever-increasing number and variety of or- 

 ganic substances are being found in it. 

 Although there is very little organic mat- 

 ter in sea water quantitatively speaking. 



evidence is accumulating that the little 

 there is exerts an important infljience on 

 marine life (Collier, 1953; Lucas, 1955; 

 Nigrelli, 1958) . Among the various types 

 of organic substances that have been found 

 in sea water are enzymes, vitamins, pig- 

 ments, amino acids, antibiotics, and toxins, 

 most of them presumably produced as ex- 

 ternal metabolites or ectocrines by plants 

 and animals in the sea. The role that such 

 minute constituents of sea water can play 

 in maintaining marine life in captivity has 

 been determined for only a few microor- 

 ganisms, and their fate, when subjected 

 to the changes that "captive" sea water 

 undergoes, is unknown. Nevertheless, 

 their existence is noted here because of 

 the good possibility that some of them may 

 be important in the culturing of larval 

 forms and macroscopic invertebrates. 



"Wliatever may be their bases, the dif- 

 ferences between various natural sea 

 waters can be extraordinarily subtle, as 

 the decade of painstaking work by Wilson 

 and Armstrong has shown. Faced with 

 similar mysteries, aquarists have attrib- 

 uted a sort of elan vital to sea water and 

 called it "living" — for instance, when 

 they have observed that artificial sea 

 water had to be inoculated with some of 

 the natural stuff before most invertebrates 

 and some fishes would live in it. Vitalism 

 is not the answer, of course, but there are 

 vital constituents of sea water that are 

 still unrecognized. 



CHANGES OCCURRING IN SEA WATER REMOVED FROM THE SEA 



Within 30 minutes after a volume of sea 

 water has been taken from the sea, detect- 



able chemical changes have occurred in it 

 (Collier and Marvin, 1953). Biotic ac- 



