327 



portion of San Francisco Bay proper, however, indicates that tiie lower sahnities 

 prevaiHng in San Pablo Bay (see figs. 93 and 94) afford the deterring factor. 

 Some experimental evidence on this point will now be considered. 



Effects of Low Salinity on Limnoria 



There are two aspects of the effects of low salinity; one is the lellial or death- 

 producing salinity, the other is the salinity at which the normal activity of the organisms 

 is definitely retarded. 



In order to determine the lethal salinity a series of glass jars of three litres' 

 capacity were filled with sea water which had been diluted in varying amounts. The 

 actual salinities were determined by titration at the conclusion of the experiment. 

 As it is difficult to observe Limnoria directly without disturbing them, it was found 

 more feasible to judge their condition by the amount of wood discharged during a 

 given period. 



In studying the lethal salinity the discharged wood was allowed to settle in Petri 

 dishes placed in the bottoms of the jars. It was removed daily and an estimate made 

 of the amount of wood present in each jar. The pieces of wood in each jar were all 

 taken from the same test-board and contained approximately equal numbers of 

 organisms. The results are given in the accompanying table (table 45). It will be 

 seen that no wood whatever was discharged in jars No. 2 to No. 5, nor in No. 6, in a 

 salinity of 6.5 parts per 1000. At this and lower salinities all of the organisms died 

 within 24 hours. In jar No. 7, in a salinity of 10.7 parts per 1000, the discharge of 

 wood was extremely small. The organisms in this jar were very sluggish and were 

 not able to swim after two weeks. In salinities of 12, 14, 16 parts per 1000 there was 

 a gradual retardation of activity, but during the two weeks of the experiment the 

 organisms in these salinities survived and continued to bore. It therefore appears 

 from these experiments that a salinity as low as 6.5 parts per 1000 is lethal within 

 24 hours, that a salinity of 10 parts per 1000 probably is ultimately lethal and that 

 in salinities of 12, 14, 16 parts per 1000 there is a very decided retardation in activity. 



TABLP: No. 45 



SALINITIES LETH.AL TO LIMNORI.A 



The numbers refer to the wood discharged, the amount discharged in a salinity of 10.7 parts per 

 1000 being taken as 1; they represent approximate estimations only. 



In order to determine the actual retardation in activity of Limnoria by low 

 salinity, we carried out a similar experiment to the above, but allowed the discharged 



