78 



periods, periods of more of less suspended activities or of deteriorat- 

 ing influences, while the most critical factor of all is the maximum 

 number of days between periods of given salinities, especially the lower 

 ones. It is during these intervals of low salinities that the more saline 

 contents of the water in the wood and in the burrow and the mantle 

 cavity of the Teredo are being gradually or intermittently diluted. 



This table shows that at both Port Costa and Martinez at the bot- 

 tom at high tide, that is, under most favorable conditions, for the period 

 of low salinities of 163 days from November 19 to April 30, the salinity 

 was at the lowest level (below 1 part per 1000) for 33 and 17 days at 

 Martinez and Port Costa, respectively, with an average of 3 and 3.4 

 days between recurrent higher salinities, and a maximum stretch of 

 15 and 12 days, respectively. These results approximate those of the 

 laboratory tests. The number of days at or below a given salinity and 

 the average and maximum length of periods of tension between recur- 

 rent higher salinities steadily increase as the parts, per 1000 increase. 

 In other words, at the mud line and all points above, at Port Costa 

 and Martinez, from November 19 to April 30 Teredo was repeatedly ex- 

 posed to a tension of salinities which were lowered beyond the experi- 

 mentally determined breaking point, that is, for more than nine days. 

 Exposures to higher salinities were insufficient in saline content and 

 too far apart, at least in one instance within this period, to permit 

 Teredo to survive. 



The survival of Teredo in minimal amount near the surface at the 

 Carquinez Strait Light about one mile below Crockett is indicative that 

 salinities at that level represent approximately the survival level of 

 these environmental conditions for this species of borer in an area of 

 changing tidal waters. The graphs of salinities of > samples taken at 

 low tide at Crockett from four feet below the surface are shown in plate 

 16, and are analyzed in the accompanying table. 



