74 



L. J. HALE 



FLANGES BOLTED 

 TOGETHER 



ENDS OF ,-^ 



ADJACENT TANKS 



Figure 5. — Tank-connecting units. 



Swirling of the water is to be encouraged, 

 but increasing the speed of entry of water 

 with a smaller bore pipe (to get more 

 swirling) results in an increase in the head 

 of water and reduces the efficiency of the 

 pump, so that a compromise is necessary ; 

 2-inch bore pipes are used on the aquarium 

 here. 



Tidal conditions 



A closed circulation system enables tidal 

 conditions to be easily simulated by a 

 sluice gate. A round hole is cut in one of 

 the broad sides of a Perspex box so that 

 it may be fixed to a tank connecting unit. 

 The opposite broad side is cut down so as 

 to be at the level of the water. The sluice 

 gate, also of Perspex, slides in slots against 

 this side of the box. One end of a pivoted 

 arm is attached to the sluice gate, the other 

 end resting on a cam turned by an electric 

 clock motor. Thus the sluice gate rises 

 and falls once every 12 hours; as it rises, 

 the depth of water on the upstream side 

 increases, and therefore decreases on the 

 downstream side ; as the gate falls, the two 

 water levels reverse this change until they 

 become equal again. 



Tidal conditions are necessary for some 

 intertidal organisms. It has been found 

 that limpets, for example, live indefinitely 

 in these tidal conditions, but were difficult 

 to keep for long without them. 



Filtration 



For the reasons already stated the water 

 in the aquarium is not filtered. It would 

 be expected that detritus would slowly col- 

 lect in the tanks, and this does happen. 

 This detritus appears to have no delete- 

 rious effects on most organisms, but it does 

 tend to swamp some smaller, sedentary 

 types. 



An obvious method of control is to re- 

 move it from time to time, but in the ab- 

 sence of knowledge as to the nature of the 

 detritus this practice might upset the 

 chemical balance of the aquarium. A bet- 

 ter method is to introduce detritus feed- 

 ers; hermit crabs have been used success- 

 fully. 



It is worth mentioning that in spite of 

 the slow accumulation of detritus the wa- 

 ter always remains perfectly clear. 



Lighting 



Fluorescent lighting is provided for 

 some tanks. The amount of lighting, in- 

 cluding the time it is switched on, is ad- 

 justed so that the photosynthetic orga- 

 nisms (especially diatoms) keep the pH of 

 the water to about 8.1-8.2. 



ACKNOWLEDGMENTS 



It is a pleasure to record my apprecia- 

 tion of the hospitality of the Director and 

 Staff of the Stazione Zoologica, Naples, 

 where these ideas about marine aquariums 

 were first conceived, and the helpful dis- 

 cussions with many colleagues. I should 

 also like to thank Mr. A. Yeoman, Mr. 

 A. Gall, and Mr. R. A. Fox whose craft- 

 manship made the aquarium possible. 



