70 



L. J. HALE 



nitrate. It will accumulate as nitrate un- 

 less removed by photosynthetic plants. 



Other major constituents of sea water 

 are unlikely to alter significantly, but the 

 concentration of some minor constituents 

 may do so. For example, phosphate is 

 removed by plants and some animals, and 

 excreted by animals but information on 

 this ion is too meager to make a useful 

 assessment of the situation in an aquarium. 

 Other ions, such as iodide, silicon, and 

 copper, may become depleted when par- 

 ticular organisms requiring them are kept 

 in the tanks. 



Suspended particles 



Marine bacteria are largely sedentary 

 (ZoBell and Anderson, 1936) ; nitrifying 

 bacteria are found associated with sus- 

 pended particles. These particles may 

 adsorb ammonia (Cooper, 1948a), thereby 

 encouraging bacterial oxidation. 



Most of the iron in the sea occurs 

 as colloidal particles (Cooper, 1948b; 

 Cooper, 1948c ; Harvey, 1937b) . Nitrify- 

 ing bacteria require iron (Spencer, 1956), 

 as also do diatoms (Goldberg, 1952; Har- 

 vey, 1937a) which are useful photosyn- 

 thetic organisms in an aquarium. Sus- 

 pended particles are essential as food for 

 filter- feeding organisms. Thus suspended 

 particles are an important feature of the 

 marine environment, and the common 

 practice of filtering aquarium water would 

 appear to be harmful. 



Water movement 



The necessity for an active movement 

 of water in an aquarium is indicated by 

 the fact that the majority of organisms 

 kept therein are relatively sluggish or 

 sedentary. The materials they require 

 for their existence which are contained in 

 the water, and the desirability of flushing 

 awa^y excretory products, must therefore 

 be mediated by the water. Marine orga- 

 nisms fall into three main groups as re- 

 gards these materials. Firstly, there are 



the animals and the aerobic putrefying 

 bacteria; they require oxygen, and their 

 waste products include carbon dioxide, 

 ammonia, and some inorganic phosphate 

 and sulphate. Secondly, there are the 

 nitrifying bacteria requiring oxygen, am- 

 monia, and phosphate, and producing car- 

 bon dioxide and, ultimately, nitrate. 

 Thirdly, there are the photosynthetic 

 plants which, in the presence of light, 

 more importantly require inorganic nitro- 

 gen, phosphorus, sulphur, and carbon di- 

 oxide; they give off oxygen. Thus the 

 requirements of one group are the waste 

 products of anotlier, and a stream of water 

 is the obvious means of transportation of 

 these materials. 



To this must be added the function of a 

 moving stream of water in supporting sus- 

 pended particles. 



There may be other beneficial proper- 

 ties of an active water movement. For 

 example, marine hydroids become mori- 

 bund and die in 1 or 2 days in stagnant 

 water, but they will live indefinitely in a 

 moving stream of sea water (Hale, 1960a, 

 1960b). The reasons for this remain 

 obscure. 



In the aquarium here a rate of flow of 

 water of 10 feet per minute is maintained 

 and is generally satisfactory. Faster and 

 slower rates are found in different parts 

 of a tank. The flow may be increased 

 considerably by the use of baffles. 



Temperature 



Consideration of the literature on the 

 temperature tolerance of marine orga- 

 nisms indicates that a temperature up to 

 at least 20° C. is not harmful to organisms 

 trom temperate seas. The water tempera- 

 ture in the aquarium here has risen to 21° 

 C. without noticeable effect on the con- 

 tained organisms. 



DESIGN OF AQUARIUM 



This brief survey of aquarium condi- 

 tions points to a simplicity in the design 



