There usually are no hard-shelled forms below the photic and/or mixed 



layer zone (Figure 7) . ' Table 7 lists general relationships between 



depth and geographic location for some fouling organisms. Marine borers 



were found attached on "all" surfaces at various depths (down to 7000 ft) 



in protected areas away from water currents. These borers have been known 



to bore into materials which were "unborable," e.g., lead, concrete, 

 ^., 63,68,72 



6 9 12 15 18 21 24 



DURATION OF EXPOSURE (months) 



27 



Figure 7 - Time to Reach Hard-Shelled Fouling Stage as 

 a Function of Depth 



The most generally accepted boundary for "insignificant fouling" is 

 65 miles offshore.'^ At this and greater distances, the fouling, although 



present and often bothersome, is reduced to manageable levels.'^ Not only 



72 

 is the quantity lessened, but also the species diversity is small; an 



antifouling system could be less complex as it would need only a narrow 



spectrum toxin. 



29 



