10 



JAMES W. ATZ 



in which they live (see fig. 1). Early 

 aquarists considered their aquariums and 

 water systems to be microcosms whose ele- 



ments behave in the same way as they do in 

 the whole earth's grand economy (e.g., 

 Lankester, 1856; Mather, 1880), and this 



Figure 1. — Diagram of the complex interactions of macroorganisms and microorganisms and envi- 

 ronment in a marine aquarium or sea-water system. Arrows point from the agent or influencing 

 factor to the item changed or influenced. 



attractive but erroneous idea has persisted 

 for many years (see Stowell, 1926a). As 

 a consequence, the early aquarists who dis- 

 covered such vital techniques as circulat- 

 ing the sea water, storing it in the dark, 

 and aerating it, attributed their usefulness 

 to quite incorrect reasons (Lloyd, 1871; 

 Newman, 1878). Standing on the shoul- 

 ders of these pioneers, we now recognize 

 many significant differences between the 

 bionomics of aquarium systems and the 

 sea. 



The need for constant treatment of sea 

 water in order to keep it satisfactory for 

 marine life is apparent. x\.t the very least, 

 sea water must be aerated continuously, 

 but unless it is to be replaced often and 

 unless the ratio of volume of water to 



volume of animals living in it is extremely 

 large, circulation, filtration, and storage 

 in some sort of -reservoir are also neces- 

 sary. In a typical circulatory system, the 

 water flows from tank (exhibition, hold- 

 ing, or experimental) to filter, to reservoir, 

 and back to tank (see fig. 2). Aerators 

 are frequently located between each of 

 these units and the next. The pump is 

 placed after the reservoir because it is 

 least likely to become clogged with ani- 

 mals, sand, or solid wastes at this spot. 

 A gravity tank greatly facilitates the reg- 

 ulation of water flow into the animals' 

 tanks and lessens the chance of introduc- 

 ing water supersaturated with air. 



Systems in which the water is recircu- 

 lated, being used over and over, are called 



