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CHAPTER XVI 



THE BIOLOGY OF TEREDO NAVALIS 



In undertaking an investigation of the biology of a group of organisms, it is 

 usually most feasible to select a single species as a type for a thoroughgoing study, 

 and to consider the others by comparison with it, rather than to attempt what in 

 the nature of the case would be a more or less superficial investigation of the group 

 as a whole. In the present case, accordingly, Teredo navalis has been selected as a type 

 for particular study, this in view of its widespread distribution, its unusual adapt- 

 ability to the conditions of new environments, its extraordinary capacity for speedy 

 and complete destruction of timbers exposed to its ravages, and especially its recent 

 unprecedented depredations in San Francisco Bay. 



In the following pages are presented a somewhat detailed account of the biology 

 of this organism, the history of its introduction to and subsequent liehax'ior in San 

 Francisco Bay, and its relation to physical factors of the environment, especially 

 with regard to the conditions which are favorable or otherwise to its growth and re- 

 production, and the iuA-asion of previously uninfected localities. 



The record of Teredo navalis, since our earliest knowledge regarding it, has been 

 a history of sudden and usually calamitous, because unexpected, invasions. It is 

 therefore a matter of the highest importance to analyze the conditions which permit 

 such recurring outbreaks, in order that they may be anticipated in future, here and 

 elsewhere, and steps be taken to avoid a repetition of such disasters as that which has 

 afforded the occasion of this investigation. 



THE HISTORY OF TEREDO NAVALIS IN SAN FRANCISCO BAY 

 At the entrance to Mare Island Strait, at the northern extremity of San Pablo 

 Bay, three long dykes of wooden piling were erected about 1905. The purpose of 

 these dykes was to direct the tidal currents in such a way that the channel should not 

 become filled with silt. Untreated piling was used in the construction of the dykes, 

 as in marine construction generalh- in this portion of San Francisco Bay. Shipworms 

 had not been known to occur at all in the upper reaches of the bay, and it was con- 

 fidently believed that the lowered salinities which prevailed as a result of the inflow 

 of fresh water from the San Joaquin and Sacramento rivers constituted an effectual 

 deterrent to these organisms. Consequently it was a matter of considerable surprise 

 when, in January, 1914, an inspection of the Mare Island dykes showed extensive 

 damage by shipworms. 



In the spring of the same year damage by these organisms was also noticed in 

 the piling of a wharf on the opposite side of the bay, a half mile below Crockett, and 

 about the same time it was discovered that piling in the dock of the Union Oil Company 

 at Oleum had been similarly attacked. It is probable that shipworms would have been 

 found in the piling of other docks in this neighborhood at this time if a search for them 

 had been made; but the damage was not sufficiently serious to attract general atten- 

 tion. Barrows (1917) states that in this first attack much of the brace piling of the 

 dykes was more than half eaten through, but the sheet piling, which was somewhat 

 less exposed, was not so heavily attacked. 



The organism occasioning this damage was at first believed, on the basis of an 

 identification by Dr. Paul Bartsch of the U. S. National Museum, to be Teredo 

 diegensis, but was subsequently found to be identical with the Teredo navalis of 

 European waters. 



