In mantis shrimp Squilla empusa the serum magnesium, calcium, and 

 potassium decreased with decreasing salinity (Lee and McFarland 1962) , 

 Below 60% seawater the calcium level remained constant, at a concentra- 

 tion which appeared similar to the blood calcium level in our studies. 



Concentrations of blood calcium, magnesium, and potassium were 

 measured in crabs Hemigrapsus nudus and H. oregonensis in eight sa- 

 linities (6 to 175% seawater) and three temperatures (5°, 15°, and 

 25°C) (Dehnel and Carefoot 1965; Dehnel 1966, 1967). In 6 to 75% 

 seawater the blood potassium and calcium were considerably hypertonic 

 to the external salinities. In 100 to 175% seawater the ion concen- 

 trations approached isotonicity. The potassium regulation is in 

 agreement with our findings in P^. aztecus ; but calcium regulation 

 paralleled the isosmotic line in 25 to 36°/ooS range. The shrimp 

 acclimated at 18°C exhibited isosmocity between 32 to 36°/ooS level 

 at 18° and 32°C. Blood magnesium in the crabs was hypotonic in all 

 salinities above 12% seawater. 



In H. nudus and H. oregonensis test temperatures exerted no in- 

 fluence on the regulation of blood potassium and calcium. High tem- 

 perature impaired the magnesium regulation. There is contrary evidence 

 in brown shrimp that temperature variations influence the calcium, po- 

 tassium, and magnesium regulation. Potassium concentration levels in 

 shrimp increased with test temperature regardless of acclimation tem- 

 perature. Temperature was shown to influence the regulation of cal- 

 cium and magnesium. Evaluation of the physiological implications of 

 these ionic changes is beyond the scope of these experiments. 



However, changes in the ionic ratios in the test salinities are 

 shown to influence the behavior, survival, and metabolic rates in 

 brown shrimp. High or low sodium levels used in these studies evident- 

 ly have no effect on the behavior and survival. Removal of magnesium 

 from the salinity medium at 18°C increased the activity level above 



292 



