350 University of California Publications in Zoology [ VoL - 22 



INTRODUCTION 



Teredo navalis inhabits a very wide range of salinities. In 

 Holland (Vrolik, et al, 1860-1864; Van Oordt, et al, 1865) these 

 borers were found at points practically exposed to the open sea at 

 Vlissingen on the North Sea at the mouth of the Schelde River, where 

 the salinity remains near 30 parts per 1000, and at Harlingen on 

 the Zuider Zee, where the salinity ranges between 20 and 30 parts 

 per 1000. They also inhabit the brackish waters of the Ij near 

 Amsterdam, where the salinity falls as low as 6 parts per 1000. In 

 San Francisco Bay (Kofoid, 1921-1922) Teredo navalis was estab- 

 lished by the autumn of 1920 not only in the more saline waters at 

 Goat Island and along the San Francisco waterfront, but also in the 

 brackish waters of Carquinez Straits and the Delta of the San Joaquin 

 River. 



Barrows (1917) described the initial infection of the Mare Island 

 dikes and other structures at the head of San Pablo Bay in 1912- 

 1913 by a species of Teredo identified at that time by Bartsch as 

 T. dicgensis, which was undoubtedly T. navalis. Since that time 

 Teredo has spread rapidly into the fresher waters of Carquinez 

 Straits (Kofoid, 1921) and upstream as far as Antioch on the San 

 Joaquin River, twenty miles from San Pablo Bay and fifty from the 

 Golden Gate. 



In the region of Carquinez Straits and upstream from this point, 

 the salinity of the water is subject to great changes, varying with 

 tides and with seasonal fluctuations of the discharge of the San 

 Joaquin and Sacramento rivers. The seasonal variation of the 

 salinity is of great importance with regard to the distribution of the 

 borers, as at some points the salinity is high enough for their survival 

 only during certain months. Thus, although the borers were able to 

 establish themselves above Carquinez Straits during the summer and 

 fall months when the rivers were low and the salinity comparatively 

 high, they were nevertheless killed off there during the winter and 

 spring months of extreme run-off and low salinity. The critical point 

 seems to be at Carquinez Straits. There, in some years, the salinity 

 is lowered sufficiently to kill off at least a large proportion of the 

 teredos, while, in other years, it remains high enough to allow nearly 

 a total survival. 



