FOULING OF SHIPS' BOTTOMS 239 



light. More recently, Caswell Grave (1920 and 1923) and his students have shown 

 that the larvae of several tunicates (Amaroucium, Perophora, and Botryllus) are 

 positive to light upon hberation from the mantle chamber of the adult, but at the 

 time of attachment all are definitely negative to light. Thus Grave and Woodward 

 found for Botryllus (a tunicate common on our North Atlantic coast) that the free- 

 swimming period for these larvse persisted for from 1 to 27 hom-s, and that during 

 this time they react positively to Ught for a "comparatively long period," and then 

 are indifferent or nonresponsive and finally negative to Ught for a "period of short 

 duration just before metamorphosis begins." 



Some work has been done on the reactions of the barnacle larvae to light, notably 

 by Jacques Loeb (Groom and Loeb, 1890); but this work was done only on the early 

 larval stages (nauplii) and consequently has httle bearing on the problem, as the 

 cyprid stage is the condition in which the barnacles attach to ships' bottoms. In his 

 studies of the "nauplean larvae" it was found that they were usually positive to light 

 upon liberation from the parent, but that reversal of reaction frequently occurred, 

 probably dependent on environmental factors. 



That practical tests have been made on ships' bottoms regarding the effect of 

 colors is recorded by Holzapfel (1923), who concludes that the advantageous effect, 

 if any, is too slight to warrant any serious consideration. However, the report of 

 Captain Macauley (1923) would indicate that not all nautical men would so minimize 

 its practical importance. 



As this problem (the effect of light on fouhng) seemed one that offered consider- 

 able possibilities, and inasmuch as no controlled experimental data were available 

 regarding it, considerable time has been spent on its study. This work has been of 

 four kinds. First, the use of steel plates coated with variously colored paints, 

 submerged in a tidal channel whose waters were heavily infested with fouling organ- 

 isms; second, the study of the effect of a submerged electric Hght on the attachment 

 of organisms (the results of this experiment were so inconclusive, due to various 

 difficulties, that they are not presented here); third, the use of colored tiles under 

 similar conditions in order to ehminate the possible effect of the constituents of the 

 paint film, leaving only the effect of light; fourth, laboratory studies of the reactions 

 of the cyprid larvae of various species of barnacles to Hght of known intensity and 

 spectral distribution; and finally, as a coroUary of this, the study of the actual 

 process of attachment and the effect of light at the time of attachment. 



SUBMERGED TEST PANELS 



Attachment of fouling growths on steel panels painted with materials of different 

 colors has been studied by several workers. Soon after beginning this investigation 

 a conference of men working on the various aspects of the problem of fouling of 

 ships' bottoms was held at Beaufort, N. C, on October 25, 1922, where large numbers 

 of panels had been submerged to test the effectiveness of as many different paints. 

 Already at this time a series of panels painted with different colored paints had 

 been submerged at the suggestion of H. A. Gardner. As he states in his circular 

 (1922) recording the fact that these were submerged, but without recording any 

 results, these were submerged "to determine the effect of colors upon attachment of 

 barnacles. It is believed that the barnacles might seek, through protective colora- 

 69861—28 4 



