FOULING OF SHIPS' BOTTOMS 247 



On several occasions the writer has been fortunate in seeing the actual process 

 of metamorphosis while observing through a microscope. It was observed that after 

 attachment by means of the antennse the organism would "kick" vigorously for 

 some time, but without eflFecting release. The animal then appeared to become 

 fixed and metamorphosis followed. The two-valved shell of the cyprid stage was 

 thrown off, as was also the exoskeleton of the appendages and usually the paired 

 eyes as well. From this almost amorphous mass, the young barnacle soon emerges. 

 A secretion continues to be laid down on the formerly ventral surface, and the 

 rudiments of a coating (the future shell) appear around the sides of the mass. 

 Whereas, when attached, the appendages extend downward, they now extend upward, 

 and the mouth parts also have changed their position. A more complete account 

 of this process and related phenomena is given by the author (Visscher, 1928). 



It is thus apparent that barnacle larvae "test" the surface to which they attach, 

 and at no time do the bodies of these organisms come into direct contact with the 

 surface to which they attach. 



DISCUSSION AND CONCLUSIONS 



From the data presented in this report it is apparent that fouling occurs almost 

 entirely when ships are in port. For this reason passenger ships were found to be 

 almost free from fouling, while ships temporarily out of commission, and battle- 

 ships, were consistently the most severely fouled. It is accordingly apparent that 

 vessels should be held in port as short a time as possible. 



Fouling growths usually are killed if the vessels move from one port to another 

 at a considerable distance. This is due, no doubt, to the differences lq temperature, 

 salinity, and dissolved salts of various kinds. However, the death of the organism 

 does not necessarily free the ship from its fouling. Only the living portions are killed 

 and the shells often remain for many months. If, on the other hand, a vessel moves 

 into another port while the fouling growths are stiU young and succulent, such 

 growths probably die and fall off completely, thus ridding the vessel of all fouling 

 matter. 



Fresh water also has been shown to cause the death of most organisms that 

 produce fouling. However, the same results are found here as above; namely, that 

 if heavy calcareous shells have already formed, the fresh water merely stops increase 

 in growth but does not remove most of the material already there, unless it is very 

 young and its parts are still soft. 



Metal has been shown to remain free from fouling growths as long as electro- 

 lysis takes place and its ions are hberated. As this occurs normally, in sea water, 

 for copper, this material will not foul heavily with most types of organisms unless 

 such ionization is inhibited. It is evident, then, that to be effective it must be in 

 such a condition that it will be wasting away continually, going iuto solution. 



The efficacy of poison paints has been questioned because of biological considera- 

 tions relating to the activities of the larvae at time of attachment. It has been shown 

 that the only time when a poison carried in a paint film can be effective is at the time 

 of attachment of the fouling material. Immediately after this a film of calcareous 

 or allied material is deposited by the organism and separates its tissues from the 

 paint. Many vessels and experimental plates have been observed that had become 



