1922] Blum: On the Effect of Loir Salinity on Teredo Navalis 367 



SUMMARY 



Experimental observations on the activity of Teredo navalis in 

 various salinities, as manifested by the extension of the siphons, indi- 

 cate that the organism is normally active in salinities as low as !) parts 

 per 1000, and below this point the activity decreases with decrease in 

 salinity. Below a salinity of 7 parts per 1000, the proportion of active 

 individuals decreases very rapidly until at 3 parts per 1000 no 

 teredos are extending their siphons. 



The average lethal salinity for Teredo navalis lias been determined 

 experimentally as 5 parts per 1000. 



Teredos obtain some protection from water of a salinity below 

 the lethal (5 parts per 1000) by stopping the mouth of the burrow 

 with the pallets and thus preventing the entrance of water from the 

 outside. At the same time, a supply of salt water is held within the 

 burrow. It is probable that the salinity of this retained water is 

 gradually diluted by diffusion through the wood and thai the 

 organisms are finally killed in this way. If, however, the salinity rises 

 above 5 parts per 1(100 before the salinity of the retained water 

 becomes diluted enough to kill the organism, it will be able to obtain 

 a fresh supply of water and survive for a longer period. 



A period of thh'ty-three days below 4 parts per 1000 salinity has 

 destroyed 90 per cent of the teredos in piles at Crockett. Immedi- 

 ately prior to the above period, an interval of twenty days below 

 5 parts per 1000 salinity occurred, but the record shows frequent 

 peaks of 1 parts per 1000 salinity or more during this interval. It is 

 probable that the salinity actually rose to 5 parts per 1000 at some 

 time during the days on which these peaks occurred, since the water 

 samples were not always taken at the major tide. Thus it seems 

 reasonable to measure the period of survival as the period below 4 

 parts per 1000 salinity, i.e., thirty-three days. The period necessary 

 to destroy the surviving 10 per cent of the organisms is impossible to 

 determine definitely at present. 



Teredos show remarkable recovery from sudden changes of salinity 

 in aquaria. They have also survived great changes in the salinity of 

 the bay water during the past season. 



