HANSON and BELL: SUBTIDAL AND INTERTIDAL MARINE FOULING 



One must also recognize that data collected from 

 static test panels can only give a limited indication 

 of the growth rate of fouling organisms in a 

 continuous-flow cooling system (Dobson 1946). 

 Fouling organisms naturally dependent upon 

 water currents to supply food, may have their 

 growth rates enhanced by the greater water veloc- 

 ities of a continuous-flow cooling system (Dob- 

 son 1946; Benson et al.^). Mawatari^ observed, 

 however, that test panels exposed in current ve- 

 locities of 4 to 7 m/s remained totally free of 

 fouling organisms. Efforts to reduce the influence 

 of static plates have been made by several authors 

 (Smith 1946; Doochin and Smith 1951; Wood 

 1955), but these efforts have produced conflicting 

 results. 



Several additional factors should be mentioned 

 which influence both the growth rate and the 

 species composition of sessile organisms coloniz- 

 ing test plates. The larvae of barnacles and many 

 other fouling organisms have been found to be 

 negatively phototrophic when they attach to a sur- 

 face. Therefore, these organisms prefer to attach 

 to shaded or dark surfaces (Visscher and Luce 

 1928; Thorson 1964). Also, surface texture has 

 been shown to affect the rate of attachment of 

 settling larvae (Crisp and Ryland 1960; Pomerat 

 and Weiss'). In general, porous and rough surfaces 

 have the greatest fouling accumulation. 



All of these factors influenced the results ob- 

 tained by the present study. For example, the test 

 plates, although they were subjected to natural 

 flow currents of the marine environment, were not 

 subjected to the "unnatural" flow currents of a 

 power plant cooling system. Thus, fouling on the 

 test plates might be somewhat different from the 

 fouling of a cooling system. Yet the test plates offer 

 useful indications as to what will happen in 

 the actual cooling system and therefore they are 

 useful for predictive planning of power plant 

 engineers. 



In the present study, vgu-iations in the abun- 

 dance and species composition of fouling or- 

 ganisms were observed for the different construc- 

 tion materials. Accumulation was slow on the 



«Benson, P. H., E. L. Littauer, and N. P. Stumbaugh. 1968. 

 Outlook for rriEirine corrosion and fouling protection. Paper pre- 

 sented at Symposium on Ocean Technical Problems of the 1970's. 

 61st Annu. Meet., Los Ang., Calif, Dec. 1968, 42 p. 



^awatari, S. 1965. Protection of power plants from biological 

 fouling. Unpubl. rep. Research Institute for Natural Resources, 

 Tokyo, Jap. 



■'Pomerat, C. M., and C. M. Weiss, 1946. The influence of 

 texture and composition of surface on the attachment of seden- 

 tary marine organisms. Unpubl. manuscr. 



copper-nickel alloy plates, but was rapid and com- 

 plete on the concrete and wood plates. Because the 

 fouling plates were exposed to identical environ- 

 mental conditions, the differences in fouling resis- 

 tance must have been dependent upon the differ- 

 ences between the media. Previous research has 

 shown the same results — Woods Hole Oceano- 

 graphic Institution (1952), for example, found 

 that copper-nickel alloy maintains its fouling 

 resistance for 10 mo, much longer than concrete 

 or wood. 



Depth was found to have a significant effect 

 upon the rate of fouling accumulation. For exam- 

 ple, the dry weight of removable material from all 

 materials placed below the surface level ( 1 m) was 

 negligible except for those wood and concrete 

 plates colonized by Balanus crenatus. Yet at the 

 surface there was considerable algal and 

 diatomaceous growth on all media except the 

 copper-nickel alloy. The only organism which in- 

 creased in density as the depth increased was B. 

 crenatus, the only organism colonizing the plates 

 at the 15.3-m level. Because these results were 

 similar for all media and because they were cor- 

 roborated by qualitative examinations made on 

 the ropes, floats, and anchors, it appears that a 

 cooling system intake in the Kiket Island area 

 should be sited in water deeper than about 6 m. 

 Based on biofouling results, the cooling system 

 intake should not be sited at the surface because 

 fouling is greatest at that level. 



An analysis of the seasonal distribution of the 

 fouling organisms showed that there was initially 

 an accumulation of brown detrital film and bacte- 

 rial slime on the fouling plates. Soon a filamentous 

 algae, Enteromorpha, and a diatom, Melosira, be- 

 came established. As floral density increased, 

 greater numbers of Crustacea were observed liv- 

 ing in the growths on the plates. Barnacle and 

 mussel colonization of the test plates occured 

 throughout the year, but was greatest from April 

 through October. For mussels, at least, it ap- 

 peared that a previous accumulation of fouling 

 material was required before the mussels would 

 attach to the test plates. Thus, it would appear 

 that fouling control should be greatest during the 

 spring, summer, and early fall. During late fall 

 and winter fouling control need not be so greatly 

 emphasized. It must be remembered that the time 

 for maximum fouling may vary from year to year, 

 and thus fouling control should be regulated by 

 routine observations of larval settlement. In ad- 

 dition, early fouling control may help to deter col- 



383 



