240 



BULLETIN OF THE BUREAU OF FISHERIES 



tion, certain colors and avoid other colors against which they might present a more 

 obvious appearance." However, at the time of the first examination by the author 

 these plates showed results that were quite inexplicable on the basis of adaptive 

 coloration but proved sufficiently interesting from a biological viewpoint so that a 

 preliminary report by the author was submitted at that time (December, 1922), 

 from which the following paragraphs are quoted: 



In order to test this hypothesis a series of 12 steel panels had been exposed. All were painted 

 with two coats of standard anticorrosive paint and a third coat which contained the desired 

 pigment. All of the pigments, as well as the paint mixtures used, were nontoxic. (See H. A. 

 Gardner, 1922.) All plates were exposed on the same day, and each panel was suspended separately 

 from a rack built in a tidal channel, where the water flows at between 4 and 6 miles per hour 

 whenever the tide is running. They were submerged in water about 6 feet deep, being held in a 

 vertical position about 12 inches from the bottom. They were arranged in a row, end to end, 

 about 2 or 3 feet from each other and parallel to the water currents in the channel. The plates 

 extended in a line approximately north and south. Both sides of each plate, consequently, received 

 about the same amount of light during the course of the day. Examination was made about two 

 months later. As all of the plates had been treated alike, except for the colored pigments, and 

 as all factors influencing them were the same, it may be concluded that any difference in the 

 amount and nature of the fouling would be dependent on color. 



The results obtained are presented in a table (No. 8) and may also be seen in the photographs. 

 (Fig. 34.) The colors of the plates shown in the photographs are as follows: 201, white; 202, 

 yellow; 203, red; 204, green; 205, blue; and 206, black. By referring to the photographs and 

 to the table it will be seen that there was much more fouling on the dark plates than on the lighter 

 colored plates. The contrast between the white and black plates was very marked. 



Table 8. — Organisms found on test panels that differed in color of paint 



Color of paint 



Clean area 



Worm tubes 



Bryozoa 



Hydroids 

 ("grass") 



Barnacles 



White (201) . 



Yellow (202) 



Red (203)... 



Green (204). 

 Blue (205)... 



Black (206) . 



Extensive (65 per 



cent). 

 Extensive (40 per 



cent). 

 Few and small (5 



per cent.) 



Extensive 



Few, medium (15 



per cent.) 

 None 



Abundant 



Very scattered . 



do 



do 



do 



Very few... 

 Abundant. 

 Many. 



do. 



do. 



0 



Very numerous. 



Numerous 



do 



0 



0 



Few. 



0 



0 



(?)- 



Few (?). 



.do. 



Many.. 



0. 

 0. 



Very few. 

 Few. 



Fairly numer- 

 ous. 



Very abundant. 



It will be noted that the clean areas were most extensive on the white (65 per cent) and yellow 

 (40 per cent) plates. The growth of very fine alga? was present only on the lighter colored plates 

 and was abundant only on the white plates. It formed almost the only growth present on these 

 plates. 



The worm tubes (irregular, slender, white formations seen in the photographs), formed by an 

 annelid worm of the genus Hydroides, appeared very numerous on all the plates except the white 

 and black. The latter may have had as many worm tubes as any other plate, but because it was 

 so densely covered by other growths the appearance of any tubes was obscured. 



The Bryozoa (characteristic circular patches seen in the photographs) were noticeably most 

 abundant on the red plates, although all others, except the white and yellow, were also heavily 

 infested. Not a single specimen was found on the white and but a few on the yellow plates. 



The hydroids (grass) were absent from all but the red, blue, and black plates, and were 

 abundant only on the last. 



The barnacles were the most striking in their distribution. Only on the blue and black plates 

 were many of them found, and they were most abundant on the black. 



