FOULING OF SHIPS' BOTTOMS 225 



Also, both from an exanunation of the logs of ships and a study of the organisms 

 found on their bottoms, that ships foul almost entirely while in harbor, and that 

 these growths usually die if the vessel leaves the original port where fouling first 

 attached, provided such movement carries the vessel to a port at some distance 

 from the original one (see Maryland and Nevada) or into a port with different ecologi- 

 cal factors, such as fresh water, polluted water, or any water considerably different 

 in temperature and related salt content, as found in most ports 500 miles or more 

 apart. 



It is thus seen that the log of a ship tells in a large measiu-e, to those able to read 

 it, the degree of fouling likely to be found on a ship at any given time, and an exami- 

 nation of the fouling material from the bottom of a vessel shows fairly accurately 

 where the vessel has been and how long it remained in various harbors. 



SEASONS AND RATE OF GROWTH 



That fouling would occur more severely at certain periods of the year than at 

 others is self-evident to all who study nature's laws. It is a well-known fact that for 

 most animals there is a limited breeding season, occurring, as a rule, but once each 

 year. Similar periodicities are found in most marine organisms, some of which 

 have been carefully studied; as, for example, the oyster (Brooks, 1880), the clam 

 worm. Nereis (LUKe and Just, 1912), and the Chitin (B. H. Grave, 1922). It seems 

 probable that aU living organisms that are subject to marked seasonal changes in 

 climate, such as temperature and salt content of the water for marine organisms, 

 as well as to seasonal changes in food, either in kind or amoimt, have seasonal perio- 

 dicities related to reproduction. Very little is known, however, regarding the exact 

 details of this question as it applies to those organisms that cause fouling on ships' 

 bottoms. Such knowledge involves a careful study of the breeding periods of many 

 species of these organisms, as well as an accurate knowledge of the habits of the 

 larvae from the time of hatching to the time when they attach and begin hfe as 

 sessile organisms. 



However, some studies that have a bearing on this problem have been published 

 recently. Caswell Grave (1920 and 1923) has studied the activities of the larvae 

 of four species of tunicates. He found that all had limited breeding periods during 

 the summer months for the region about Woods Hole, Mass. He was able to demon- 

 strate that in the species studied the larvae have a relatively short, free-swimming 

 period, varying from 1 to 28 hours. Of this time, during the first portion, in aU 

 cases, the organisms reacted toward Hght and against the influence of gravity; but 

 toward the end of the free-swimming period all reversed these reactions and were 

 negative to Hght and positive to gravity. At the end of the short, free-swimming 

 period, these organisms become attached, metamorphose, and develop at a rapid rate 

 into the typical adult form. 



The recent work of Fish (1925) is also of interest in showing the periodicity in 

 the presence of different types of barnacle larvae and other fouling agencies in the 

 waters immediately south of Cape Cod. His data show that the larvae of various 

 barnacles are foimd for almost 10 months of the year. It is for only about five of these 

 months, however, that the cyprid forms are found. Since of the forms fisted only 

 Balanus crenattis and B. eburneus are serious foufing agents, and since they attach 



