248 



at Richmond, to the unprotected piling of the dolphins at the Alameda Mole, to some 

 points in the Oakland Estuary, to Bay Farm Island Bridge and to the Dumbarton 

 Bridge at the southern end of the bay. It was also found in 1920 at South San Fran- 

 cisco, in the Bay View sewer outlet and at the sewer outlet at Hunter's Point, in new 

 piling in the boom at Islais Creek, and sparingly at Pier 7 on the San Francisco water- 

 front, in treated piling which had been opened up by Limnoria attack. Since that time 

 it has been found at Fort Point, at Tiburon, at Goat Island, at the Oakland Mole — 

 in short, at practically every locality in San Francisco Bay where untreated piling 

 has been available for examination, or where test boards have been exposed for 

 experimental infection. 



While the most spectacular damage by this organism has occurred in the brackish 

 waters of San Pablo and Suisun Bays, this is probably due primarily to the presence 

 there of a large amount of untreated piling rather than to a predilection of the borer 

 for the less saline waters of that region. Very heavy infection of test boards by it have 

 occurred at some stations in San Francisco Bay proper, notably at Goat Island and 

 at Dumbarton. Its sparse occurrence along the San Francisco waterfront and at 

 Fort Point is probably due in part at least to the absence of neighboring foci of in- 

 fection. But the optimum salinity for Teredo navalis is doubtless less than that of 

 normal sea water. It has generally been considered an organism more particularly 

 of the brackish water environment, and as a pest its activities have been particularly 

 noticeable in those regions which, on account of lowered salinities, are immune from 

 most other boring organisms. 



PHYSICAL FACTORS INFLUENCING NUMBERS AND DISTRIBUTION 



Among the physical factors of the environment which may be presumed to exercise 

 an influence on the growth and reproduction of Teredo are salinity, temperature, 

 turbidity, dissolved gases and hydrogen-ion concentration. All of these factors have 

 received consideration in the present investigation, with the result that the first two 

 have been found to be emphatically the most important. 



An analysis of these conditions as prevailing in San Francisco Bay, and their 

 observed effect on Teredo navalis will be presented in the following pages. 



Physical Conditions in San Francisco Bay 



San Francisco Bay exhibits a series of conditions of peculiar interest from an 

 ecological point of view. As regards salinity, depth, and temperature, and somewhat, 

 as well, the contour of the shores, the bay naturally divides itself into three major 

 portions, which we may term according to geographical position "upper," "middle," 

 and "lower." The upper bay includes San Pablo and Suisun Bays and the connecting 

 strait (see map, frontispiece), being bounded on the south by a line from Point 

 San Pedro to Point San Pablo. The middle bay extends from this line southward to 

 "a line through the (San Francisco) Ferry Building and Goat Island Light" (Sunmer, 

 et al., 1914, p. 22). The lower bay includes the remaining portion south of this line. 



These three divisions, taken as a whole, manifest three rather distinct sets of 

 ecological conditions. 



The upper bay represents the brackish water en\ironment, with continually 

 fluctuating salinity and maximum range of temperature throughout the year. Re- 

 ceiving at its upper end the combined discharge of the Sacramento and San Joaquin 

 rivers, this segment of the bay is very greatly affected by the inflow of so considerable 

 a quantity of fresh water. The interaction of run-off and tidal movement produces a 

 daily and almost hourly change in salinity, which is altered further by variations in 



