TABLE 2. — The relationship between temperature and the 

 approximate number of hours required for Mya arenaria to 

 acclimate to three concentrations from a control salinity of 

 16.26-17. 14°/oo. 



2 4 6 8 10 12 14 

 TEMPERATURE , °C 



FIGURE 2. — The relationship between temperature and time re- 

 quired to acclimate Mya arenaria from the control salinity 

 (30.54-31.80°/oo) to the following dilutions: (A) 11.49-12.05°/oo; 

 (B) 16.82-16.95%o; (C) 21.66-22.53°/oo; (D) 27.15-27.55°/oo. 



acclimation time (±2 SE) for all concentration 

 experiments combined at each temperature range. 



Discussion 



A constant flow apparatus is ideally suited to 

 shellfish studies. Continuous exchange of water 

 assures a rapid elimination of metabolic waste 

 products and more closely resembles natural 

 conditions than does a standing water system 



(Loosanoff and Smith 1950; Loosanoff see foot- 

 note 2). 



Van Dam (1935) observed that oxygen utiliza- 

 tion in Mya is independent of oxygen concentra- 

 tion down to about 2 cm 3 /liter (2.8 mg/liter). There 

 is therefore no reason to believe that the varia- 

 tions in dissolved oxygen encountered in these 

 experiments altered the pumping activity of Mya. 



In these studies, the exclusive use of adult Mya 

 is consistent with Matthiessen's (1960) observa- 

 tion that adult and juvenile Mya have different 

 tolerance levels to low salinity conditions. 



The phenomenon of faster acclimation to 

 concentrations than dilutions has not been 

 previously reported for Mya. Loosanoff (see foot- 

 note 2), however, reported that oysters moved 

 from 10%o into 20-25%o returned to normal 

 pumping very quickly. 



The relationship of pumping activity to shellfish 

 depuration has been well documented (Furfari 

 1966). When shellfish are subjected to suitable 

 salinity and temperature conditions, high pump- 

 ing activity is maintained and efficient depuration 

 results. 



Furfari (1966) reported that pumping activity is 

 reduced for a time when shellfish are subjected to 

 salinity other than that to which they are ac- 

 customed in the harvest area. During this time, 

 our data suggest that Mya periodically "samples" 

 the water conditions and acclimates to them 

 gradually. The length of time required is related to 

 the magnitude of the dilution. Welch and Lewis 

 (see footnote 3) have observed that this "sampling" 

 behavior is performed by opening the siphons very 

 slightly and then gently closing them, very little 

 water having passed through the clam in the 

 process. 



Our studies indicate that water temperature 

 directly influences the rate at which salinity 

 acclimation occurs. The results are consistent 

 with Harrigan (1956) who observed that the 

 pumping rate of Mya increased up to a tempera- 

 ture of 16°-20°C and Goggins et al. (1964) who 



228 



