EFFECT OF ORGANIC SUBSTANCES ON OYSTERS 



169 



identical amount, 10.5 mg./liter. The filtered sam- 

 ple, when centrifuged, showed no change. These 

 experiments having demonstrated that either the 

 10-minute centrifuging or the filtering was suffi- 

 cient to remove the particulate matter which might 

 give erratic results, we adopted centrifuging as a 

 standard part of the technique. 



VARIATIONS IN CARBOHYDRATE 

 CONCENTRATIONS IN STANDING SEA WATER 



We assumed that sea water with carbohydrates 

 dissolved in it would also contain the organisms 

 necessary for their production. Further, if the 

 sea water were kept in jars in the laboratory, 

 changes in species composition and in the numbers 

 of organisms in it would be reflected in varying 

 concentrations of the carbohydrates. If these 

 compounds were of biotic origin, they would be 

 expected to increase more rapidly with aeration 

 than without; and if the producers were phyto- 

 planktoa, production would be inhibited in the 

 absence of light. In any case, the production of 

 carbohydrates woidd not be expected if the 

 causative organisms were removed by filtering. 

 Accordingly, a set of experiments was designed to 

 vary the conditions for growth and, by inference, 

 establish which group of organisms was re- 

 sponsible for the production of the carbohydrates. 



In experiment A we filled duplicate jars with 

 fresh sea water. One was supplied with air by 

 means of a small aquarium pump connected al 

 the bottom to a sintered glass block; the other' 

 was left undisturbed. Samples were taken from 

 the center of the jars by siphons, so calibrated 

 that the water standing in them could be meas- 

 ured and discarded at each sampling. These 

 jars were kept about 15 feet from the west windows 

 of the laboratory and no lights were kept on at 

 night, an arrangement which was followed with the 

 indicated modifications in the other experiments 

 of the scries. In this experiment it was evident 

 that the production of carbohydrates was 

 stimulated by aeration (fig. 1-A). 



Agitation, as produced by the aerating appa- 

 ratus, might have stimulated multiplication of 

 the micro-organisms, and so account for the dif- 

 ferences indicated in experiment A. To test this 

 we set up experiment B, in which the surface 

 water was gently ventilated without agitation. 

 Samples were taken near the bottom of the jar 



and from the surface of the water. The results 

 show that the increased production of carbohy- 

 drates in the aerated water of experiment A was 

 not due to agitation (fig. 1-B), but to the increased 

 aeration. Here the carbohydrate concentration 

 increased more rapidly and reached a higher con- 

 centration at the surface. It appears that part 

 of the belated increase in the bottom concentra- 

 tion might have been the result of mixing due to 

 convection currents in the jar. 



In experiment C, filtered water was used to 

 determine the sequence of changes when it could 

 be assumed that the organisms which produce 

 the substances had been removed from the water. 

 As in experiment A, one jar was aerated and one 

 was undisturbed. It was quite evident from the 

 low carbohydrate concentration that the organ- 

 isms producing these substances had been re- 

 moved by filtration (fig. 1-C). 



Experiment D was designed to demonstrate 

 the role of light in the production of carbohy- 

 drates. The sequence of changes in both filtered 

 and unfiltered sea water kept in the dark was 

 followed. Xo significant changes in carbohy- 

 drate concentrations occurred in the absence of 

 ' dig. 1-D). 



From these experiments we may conclude that 

 biotic activity is ible for the production of 



carbohydrates, and that lighl and air create con- 

 ditions favorable for the organisms producing 

 these carbohydrates in sea water. It woidd be 

 expected further that the responsible organisms 

 are in part, if not altogether, photosynthetic, as 

 indicated by the increased production in the pres- 

 ence of light. The effect of aeration is not so 

 conclusive, for it is not known whether the air 

 supplied carbon dioxide to plants, or oxygen to 

 heterotrophic organisms (dinoflagellates). 



RELATION OF CARBOHYDRATE CONCENTRATION 

 TO SALINITY 



We tabulated and averaged the carbohydrate- 

 concentration values failing within salinity ranges 

 of 2%o- Plotting of these averages shows an asso- 

 ciation between the concentration of carbohy- 

 drates and salinity (fig. 2). Between about 15°/ 00 

 and 31°/oo there is an apparent negative correlation 

 between salinity and carbohydrates. From 7°/ 00 

 to about 15%o this relation is not clear and may 

 not exist. The negative relation at the higher 

 salinities may have been caused by the invasion 



