activities of specific, pre-existing regulatory organs (Kinne 1971). 

 On the other hand, acclimation results in actual changes in the re- 

 sponse mechanisms. It requires time to develop and involves all 

 levels of organismic functions and structures. Thus regulation and 

 acclimation are not alike. The capacity for osmoregulation in the 

 estuarine invertebrates depends on the time course of the salinity 

 or temperature changes. A number of euryhaline invertebrates have 

 been shown to exhibit higher capacities upon gradual changes (step- 

 wise transfer or slow variation) from normal to extreme conditions. 

 The time course of nongenetic capacity adaptation to salinity or 

 temperature seems to occur in three phases: immediate response, 

 stabilization, and a new steady state (Kinne 1971) . 



Immediate responses begin seconds or minutes after the transfer 

 of the animals into the test conditions. Frequently the responses 

 involve over- or under-shoots in activity, metabolic rates, or in 

 other performances. Changes may also occur in the behavior and 

 other physical conditions. The process of stabilization may require 

 hours, days, or weeks. Dehnel (1962) found that in the crab Hemi- 

 grapsus oregonensis the stabilization of blood osmoconcentration is 

 a function of salinity and temperature. At 15°C stabilization to 

 a 6-100% seawater range was completed within 24 hours but not to a 

 125-150% seawater range. When the temperature was lowered to 5°C 

 stabilization occurred within 24 hours to a salinity concentration 

 range of 6-150% seawater. In the same species (H. oregonensis), 

 Gross (1963a, b) noticed a measurable acclimation to 51°/ooS in more 

 than five days and a strong acclimation in 22 days. In Carcinus 

 maenas transferred from 25.9°/oo to H.8°/ooS the blood concentra- 

 tion became diluted within 26 hours and then remained constant (Duval 

 1925) . However, comprehensive information on the new steady state of 

 performance is lacking except for a few species. The crab H. ore- 

 gonensis exhibited greater capacity for osmoregulation in high sa- 

 linity after acclimation for more than 20 days to about 51°/ooS than 



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