EFFECT OF ORGANIC SUBSTANCES ON OYSTERS 



181 



SUMMARY 



During prolonged and detailed studies of the 

 effects of industrial wastes on oysters, Crassostrea 

 virginica (Gmelin) at Pensacola, Fla., we noted 

 that shell gapes and pumping rates of oysters 

 under simultaneous observation behaved in a 

 parallel manner as though responding to a com- 

 mon factor. It was found that this behavior 

 pattern was related to the concentration of cer- 

 tain organic substances dissolved in sea water, 

 and that these substances responded to the 

 N-ethyl-earbazole test for carbohydrates. 



The simultaneous recording of shell movements 

 and pumping rates was chosen as the best avail- 

 able index of physiological activity for establish- 

 ing this relation, since both lend themselves to 

 uninterrupted recording over long periods of 

 time. In analyzing these recordings, it became 

 evident that shell movements and pumping rates 

 are divided into three distinct levels, which wc 

 have defined as phases I, II, and III, each with its 

 physiological significance. In phase I, there is 

 an almost instantaneous gape on opening to 

 about one-third of the maximum gape, a less 

 rapid step closure, no pumping, and a rapid 

 response to external stimuli. Phase II, the middle 

 third of the total gape, must he regarded as a 

 transition between phases I and III, represents 

 a testing period, and probably involves only the 

 promyal and cloaca! passages, since the oyster 

 rarely passes more than 7 liters of water an hour 

 during this phase. In phase III, the oyster at- 

 tains maximum gape and pumps the maximum 

 amount of water. Because the pumping rate 

 varies with conditions, it is essential to record 

 both effluent and shell movement in interpreting 

 the effects of varying concentrations of the dis- 

 solved carbohydrates. Certain anomalies within 

 these phases were noted, including snap closures 

 while in phase III. These closures usually do not 

 enter phase II, but when they do, the rate of 

 reopening is retarded. 



An association between carbohydrate concen- 

 tration and salinity was noted, but the signifi- 

 cance of this relation remains obscure. It could 

 be the result of physical dilution of carbohydrate- 

 rich low-salinity inshore water with carbohydrate- 

 poor high-salinity gulf water, or of the adverse 

 effect of high-salinity water on the growth of the 

 organisms creating the carbohydrates. 



It was established that the oysters remove 



variable quantities (up to 50 mg./hour) of the 

 carbohydrates from sea water. 



Considerable variation in the response of indi- 

 vidual oysters to the carbohydrates were noted. 

 This would be expected, since the carbohydrate/ 

 temperature factor is not the only one to which 

 oysters respond, and these other factors must 

 often dominate the oyster's behavior pattern, 

 concealing the effects of the carbohydrates. 

 Then, too, the substances which respond to the 

 N-ethyl-carbazole test may not all be true carbo- 

 drates, or the oyster may be responding to only 

 certain of the carbohydrates within the carbo- 

 hydrate complex, whereas the test responds to all. 



The concentration of dissolved carbohydrates 

 was found to vary widely in the sea-water supply. 

 Because of this, the relation of carbohydrate con- 

 centration to pumping rate becomes obscure unless 

 the pumping rate and carbohydrate concentration 

 were measured simultaneously. A definite re- 

 sponse of the oyster in the phase of opening and 

 in the rate of pumping to the carbohydrate con- 

 centration was noted. Each oyster appears to 

 have a threshold limit to the carbohydrates below 

 which it will not pump. This threshold is raised 

 with increasing temperatures. A correlation of 

 0.78. significant at the 1-percent level, was estab- 

 lished over a long period of time using a number 

 of oysters when the pumping rate and carbohy- 

 drate concentrations were measured simultane- 

 ously. Even when a vcrage-cumulative-daily efflu- 

 ents and average-daily-carbohydrate levels were 

 compared, the relation between the two was 

 striking. Because of the raising of the threshold 

 level with increasing temperatures, it is apparent 

 thai water temperatures above 25° C. are unfavor- 

 able for oysters in regions in which the carbohy- 

 drate concentration is low. 



During the course of these observations certain 

 characteristics of these carbohydrates were inves- 

 tigated. It was established that no significant 

 changes in concentration took place when held 

 overnight either in the refrigerator or at room 

 temperature; that the concentration first increased, 

 and later decreased when exposed to daylight for 

 prolonged periods; that this increase was affected 

 by aeration; that, when filtered or centrifuged, or 

 when held in the dark, no significant change in 

 concentration took place. From these findings it 

 became evident that the carbohydrates result from 

 biotic activity. 



