Marine Aquaria 17 



A great number of investigators located in inland laboratories are 

 interested in the possibility of maintaining marine forms in a limited 

 amount of seawater, shipped to them from the nearest place on the shore. 

 For this purpose water must be collected from an unpolluted locality, 

 preferably off shore, and stored in a suitable container. Glass bottles 

 are of course ideal but not always practicable for shipping. 



If storage in glass containers is desired the ordinary carboys for spring 

 or distilled water may be used. A more practicable and cheaper way is 

 to collect and ship seawater in 25 or 50 gallon paraffined oak barrels. 

 After a few days of storage the organisms present in the water die and 

 the decomposing organic matter depletes the oxygen content of the water, 

 resulting in the accumulation of hydrogen sulphide (H 2 S). This, how- 

 ever, does not render the water unsuitable for laboratory use. By 

 aerating the sample for several hours all the hydrogen sulphide is driven 

 out or oxidized and the sulphur is precipitated and may be filtered off. 

 The author's experiments (unpublished data) show that the presence of 

 sulphur is not harmful to many marine invertebrates and that it pro- 

 motes the growth of Nitzschia cultures. 



Seawater in which marine forms have been kept may again be made 

 suitable by filtering it through a layer of gravel and sand and aerating 

 it. Increase in the concentration of salts owing to evaporation may be 

 compensated for by the addition of distilled water, while the deficiency of 

 calcium, phosphates, nitrates, and other salts used up by the organisms 

 is restored by the proper dosage of these respective substances. The 

 simplest way of controlling the concentration of salts consists in marking 

 the level of water in a tank and adding distilled water whenever the level 

 falls because of evaporation. Should a more accurate check be desired 

 the salinity of the water may be determined by titrating the sample 

 with a silver nitrate solution and finding the corresponding concentra- 

 tion in Knudsen's tables. A description of the standard method of 

 salinity determination may be found in Murray and Hjort (1912) and 

 Oxner (1920). 



Filtration. Natural seawater may contain large quantities of sus- 

 pended organic and inorganic matter which must be filtered out before 

 it is supplied to the laboratory table. For this purpose some of the 

 marine laboratories and aquaria have a more or less elaborate system of 

 filters consisting of several layers of gravel and sand through which the 

 water is allowed to pass. The institutions located far from the sea and 

 dependent in their operations upon a more or less limited supply of 

 water, as a rule filter the water as it leaves the aquarium tanks before 

 using it again. In the laboratories located on the seashore the water is 

 pumped directly into tanks in which it remains for a period of time 

 sufficient for the settling of a considerable portion of sediment. The 



