190 



the light of such knowledge he is in a position to take ad^'antage of the borers, so to 

 speak, and to consistently forestall them in his engineering practice. 



For example, in San Francisco Bay the two important species of wood-boring 

 mollusk are Baiikia setacea and Teredo navalis. The former is limited in its distribution 

 to San Francisco Bay proper, while the latter extends its range into the brackish 

 waters of San Pablo and Suisun Bays. The breeding season of Bankia setacea is 

 approximateh- from February to Juh\ that of Teredo navalis from July to December, 

 occasionalh' continuing into January. Now in engineering practice it is often desired 

 to use untreated piling for extremely temporar\- structures, such as a pipe line to a 

 dredge, or the falsework of some major structure. It could be predicted on the basis 

 of the above facts regarding the distribution and breeding seasons of the borers that 

 untreated piling driven in San Pablo Bay in February would be safe from attack 

 until July. In Suisun Bay the period of immunity would be prolonged by the factor 

 of lowered salinity, and predictions of the probable time of attack could be based 

 on occasional determinations of the salinit\' of the water. 



In the lower bay, on the other hand, no such period of immunity can be expected, 

 as both species of borer occur in this region and their combined breeding seasons 

 occupy nearly the entire year. But as Teredo imvalis breeds most actively prior to 

 November, and Bankia setacea after February, untreated piling driven in the late 

 autumn can be expected to give service for two or three months longer than if driven 

 at other seasons of the year. 



Engineers ha\'ing charge of structures in estuarine waters, where the salinity 

 varies with the tides and at different seasons of the year, can determine, from a knowl- 

 edge of the minimum salinity requirements of Teredo, whether or not it is necessary 

 to take steps to forestall attack by this borer. 



Recurring invasions of Teredo and the infestation of localities previously immune 

 are not matters of caprice, but depend upon definite combinations of conditions 

 which, properly understood, afford a practicable basis for anticipating attack and 

 adopting intelligent measures of control. It accordingly becomes imperative for the 

 engineer to familiarize himself with the conditions in his own locality, and to know 

 in advance just what problems he may have to meet. 



In the program of the investigations of this Committee considerable emphasis 

 has been placed on the biological aspects of the work. Through the continued interest 

 and support of the various cooperating agencies of the Committee and the full co- 

 operation of the University of California, it is now possible to present an extended 

 and comprehensive account of the marine borers of the Pacific Coast, and a detailed 

 analysis of the behavior of these organisms in San Francisco Bay during a four-year 

 period. In preparing the account presented below, the cosmopolitan nature of the 

 marine borer problem has been constantly borne in mind, and an attempt has been 

 made to emphasize those aspects of our findings which are of general rather than 

 merely local interest. It is accordingly believed that this account will be useful to 

 biologists and engineers at large, and it should prove especially valuable to engineers 

 and others who have to cope with the same species or the same conditions encountered 



here. 



ORGANIZATION OF THE BIOLOGICAL WORK 



The biological in\estigations of the Committee have received the services, for 

 longer or shorter periods of time, of six investigators. All have to a certain extent 

 cooperated in all phases of the work, but some mention should be made of the indi- 

 vidual contributions which the different workers have made to the progress of the 

 investigation. 



