28 Vniversiiy of California Publications in Zoology [Vol. 18 



For much of the material presented in this paper I am indebted 

 to engineers of several construction and transportation firms of San 

 Francisco and to engineers of the Union Oil Company. I wish also to 

 acknowledge the great courtesy of officers of the Corps of Civil Engi- 

 neers, United States Navy, stationed at the Mare Island Naval Station, 

 in furnishing information upon damage caused by marine wood borers 

 in wooden dikes about Mare Island. 



Genepcvl Distribution of Shipworms in San Francisco Bay 



The part of San Francisco Bay in which shipworms are most 

 active, to judge from their destructiveness, lies in the regions nearest 

 the Golden Gate, where presumably not only the salinity of the water 

 is most favorable, since it most nearly approximates that of the open 

 sea, but where a suitable food supply of plankton is abundantly 

 brought in from the ocean with the tides. 



Engineers familiar with conditions in this bay have reported a 

 certain falling off of the activity of shipworms in parts of the bay at 

 some distance from the Golden Gate, and particularly in those regions 

 where water from the open sea is not brought abundantly by the tides. 

 Thus along the North Beach wharves of San Francisco, in the vicinity 

 of Sausalito, in Racoon Strait, and about Angel Island and Alcatraz 

 Island, shipworms are extremely active. Unprotected timber in these 

 places is destroyed within a few months. On the Oakland side of the 

 bay, however, the rate of devastation of marine woodwork by ship- 

 worms is said to be slower than in the localities just mentioned, and 

 in the Oakland estuary the rate of activity of the borers is greatly 

 diminished, unprotected marine woodwork being said to last from two 

 to four years. 



In these localities where the destructiveness of the shipworms is 

 thus decreased, it is usually found that the size of the borer is also 

 reduced from a diameter frequently of one-half inch for borers taken 

 from the Golden Gate to a diameter of one-eighth inch or three-six- 

 teenths inch for borers taken from parts of the Oakland estuary. In 

 localities where the activity of shipworms is reduced, the crustacean 

 wood-borer Limnoria is often increasingly destructive. Thus Lim- 

 noria seems here to be the more active in brackish water and teredine 

 wood-borers more active in normal sea water. 



Shipworms are conspicuously absent in San Francisco Bay from 

 stagnant regions and from regions which are contaminated by sewage 

 or by factory or refinery wastes. Except in a few such regions, prac- 



