desired concentrations by adding synthetic sea salt [Instant Ocean, 

 Aquarium Systems, Inc.) or by diluting with dechlorinated tap water. 

 Salinity media were prepared with natural seawater of 30°/ooS. The 

 acclimation salinity (15°/oo) was prepared by diluting the sea water 

 with dechlorinated tap water but the test salinities 2, 5, 10, 15, 

 and 25°/oo were made by diluting the seawater with deionized water 

 (100,000 ohm/cm resistance). The other test salinity, 36°/oo, was 

 prepared by concentrating seawater with synthetic sea salt (Instant 

 Ocean, Aquarium Systems, Inc.). 



Salinity concentrations were measured with a T/S Refractometer 

 (Model 10402, American Optical Corp.). The instrument was periodi- 

 cally checked for accuracy by comparison with a portable Induction 

 Salinometer (Model RS-7A, Industrial Instruments, Inc.) using stan- 

 dard seawater as reference (obtained from lAPO Standard Seawater 

 Service, Charlottenlund Slot, Charlottenlund, Denmark). Salinities 

 were checked daily and adjusted at two-day intervals. 



Preparation of Deviated Ion Media 



For these studies, artificial sea salts were used which had been 

 specially blended by excluding one major cation such as a Ca-free mix, 

 a Mg-free mix, a K-free mix, and a 50% Na-free mix. Each of the four 

 sea-salt mixes had only one cation missing, the other ions being pres- 

 ent in the normal ratio. The salt of each eliminated cation was then 

 added to the appropriate cation-free mix in specific proportions to 

 make up salinity media in which the cation deviated from the ratio of 

 the normal amount present in seawater. Osmotic concentration of 

 each salinity medium was adjusted to that of normal seawater by the 

 addition of TRISMA-8.3 [Tris (hydroxymethyl) aminomethane buffered to 

 a pH of 8.3]. 



37 



