Unfortunately, J0rgensen does not mention the 

 dimensions, weight, or conditions of his oysters, 

 and does not describe the details of his technique. 

 He states, however, (1952, p. 362) that "the oyster, 

 Ostrea uirginica, and the ascidians Ciona intestinalis 

 and Alolyula manhattennis filter about 10 to 20 1. 

 of water for each ml. of oxygen consumed." 



The low o.xygen uptake reported by J0rgensen 

 may have been due to the experimental conditions 

 and particularly to the presence in the water of 

 graphite particles used bj' him in determining the 

 rate of water filtration. 



Environmental effects 



Seasonal changes in the rate of oxygen uptake. — 

 After spawning the New England oysters pass 

 through a period of lowered activity and tend to 

 keep their valves closed, sometimes as long as 

 2 to 3 days; when they open again the rate of 

 water transport is lower than it had been before 

 the start of the reproductive period. Through 

 the cold season of the year, from October to 

 April, the oxygen uptake remains at a low level. 

 In order to obtain comparable results and to 

 eliminate the effect of temperature, tests of 

 metabolic rates were made at 25° C, using oysters 

 that were kept outdoors and brought into the 

 laboratory for 3 to 4 days before testing to adjust 

 gradually to the higher temperature. Exam- 

 ination of the data summarized in table 27 shows 

 that the period of lowered metabolic activities 

 occurred primarily during the winter. 



EJfect of change in salinity and pH. — No sig- 

 nificant change in the respiratory rate was no- 

 ticed in water of lowered salinity to which the 

 oyster had become adjusted. In these tests 

 the metabolic rate was fu'st measured in water 

 of 31.6 7oo salinity. After the first test, which 

 lasted 6 hours, the oyster was transferred for 3 

 days into running sea water diluted with fresh 

 water to the salinity of 24.1 °/oo (approximately 

 76 percent of the previous concentration of salts). 



T.\BLE 27. — Seasonal changes in the oxygen uptake in mg. 

 of oxygen per oyster per hour of adult Long Island oysters 

 about 10 cm. long and 7 cm. wide 



The rate of respiration was measiu-ed on the 

 4th day under standard conditions. The results 

 of the test (figure 194) show that the rate of 

 o.xygen uptake in the water of lower salinity 

 was not significantly different from that observed 

 in 31.18 °/oo salinity. The tests were repeated 

 several times with different oysters with identical 

 results. In all experiments the oysters were 

 left in water of lower salinity for at least 3 days 

 to adjust to the new conditions. The effects of 

 gi-eater dOution of sea water have not been 

 studied because of the technical difficulty in 

 providing sufficient food to the oysters during the 

 prolonged periods of adjustment. 



HOURS AFTER START 



Figure 194. — Oxygen uptake of an adult Long Island 

 oyster recorded at normal salinity (solid line) of Woods 

 Hole (31.58 °/oo) and 4 days later at lowered salinity 

 (broken line) of 24.1 °/oo. All tests were made in 

 August under standard experimental conditions at the 

 temperature of 25.0° C. 



Tlie pH has a very pronounced effect on the 

 rate of oxygen uptake. The water used in 

 metabolism tests was acidified by adding a quan- 

 tity of 0.1 N hydrochloric acid. After six or 

 eight readings with normal sea water, the acidified 

 water was turned on and the testing continued 

 for another 3 to 4 hours. The curve in figiu-e 195 

 summarizes the results of all 10 tests performed 

 in July to September using Long Island and Mas- 

 sachusetts oysters. At pH 6.5 the oxygen uptake 

 drops to about 50 percent of the normal rate and 

 rapidly decreases to less than 10 percent at 

 pH 5.5. At pH 5.8 the oxygen uptake may 

 continue for several hom's at a greatly reduced 

 rate (fig. 196). 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



211 



