364 



University of California Publications in Zoology [Vol.22 



Survival Period or Lethal Stretch 



An explanation of the above process becomes important if we wish 

 to predict the survival of teredos by observation of the salinity of 

 the water from day to day. In a daily salinity record such as is 

 represented by figure 4, periods of survival or lethal stretch must be 

 measured as periods during which the salinity remains below 5 parts 

 per 1000, as when the salinitj- rises above this point the teredos are 

 able to take in a fresh supply of salt water. Fluctuations of salinity 

 during such periods must influence the rate of dilution of the water 

 in the burrow, but are of little importance in predicting the survival 

 of the organisms. 



During the past season a daily record has been kept of the salinity 

 of the water in Carquinez Straits. Samples have been taken during 

 the day at high and low tide, from the surface and from a depth of 

 fourteen feet. Samples have been taken at two points about one- 

 eighth mile apart, as it was found that differences in the salinity at 

 these two points occurred frequently because of currents and eddies. 

 In preparing the salinity graph, figure 4, the maximum and minimum 

 records from all the samples for each day have been plotted. 



TABLE 6 



Survival of Teredo navalis in Piles at Crockett during Period op Low 



Salinities, Season op 1921-1922 



* Salinity remained below 5 parts per 1000 from April 26 to June 24. 

 t Salinity remained below 4 parts per 1000 from May 17 to June 19. 

 t Salinity remained below 3 parts per 1000 from May 27 to June 19. 



Reference to figure 4 shows that during the past season (1921- 

 1922) the salinity remained below 5 parts per 1000 from April 26 to 

 June 24, below 4 parts per 1000 from May 17 to June 19, and below 

 3 parts per 1000 from May 27 to June 19. 



Table 6 shows the survival of teredos in piles pulled from the 

 fender lines at Crockett, at intervals during the period of low salinity. 



