254 



flood season in Carquinez Strait or just above, at a point that is determined anew 

 each year by rainfall and river discharge. The following experimental work (Blum, 

 1922) was undertaken with a view to determining the conditions of low salinity 

 that are unfavorable to Teredo navalis, and further the conditions that are definitely 

 lethal to the organism. 



Effect of Low Salinity 



Specimens were first acclimatized by placing them in standing water of a salinity 

 of 15 parts per 1000 for two to four days. During this period a daily record was kept 

 of the number of siphons extended from the specimen block, this number being taken 

 as the original 100 per cent for the given specimen. The specimens were then changed 

 to salinities of 0, 2, 4, 5, 6, 7, 8, 9, or 15 parts per 1000. A record was kept of the number 

 of siphons extended from each specimen block during the periods of exposure (about 

 three weeks) to these several lower salinities. Ten specimen blocks in individual 

 aquaria were used in determining the average per cent of siphons extended by the 



1924. 



Fig. 96. Section of untreated fender pile from Avon wharf of Associated Oil Co. Pulled July 29, 



teredos for each salinity tested. The number of siphons extended from each specimen 

 block was recorded each day for a period of days after an apparent maximum had been 

 reached which did not fluctuate markedly. Low records during this period, accompanied 

 by unfavorable aquarium conditions, were discarded. These values were averaged 

 for each specimen and the per cent of siphons extended was computed by comparison 

 with the number of siphons originally extended from the same block in a salinity of 

 15 parts per 1000. The average per cent for each salinity was computed from the 

 average of the ten specimens. The per cent of siphons extended in a salinity of three 

 parts per 1000 was determined separately under similar conditions, but during a 

 shorter period of exposure. 



The percentage of siphons extended from control blocks exposed during the 



