depending on the location and depth, fouling can occur on "toxic" surfaces. 

 Certain experts believe that, since the organic content of the water is 

 very low, any surface with concentrated organic compounds would foul, even 

 if these organic compounds are toxic. ' 



High biomass and fouling density on surfaces provide food for grazing 



fish. Therefore, an OTEC platform may play a beneficial ecological role 



74 

 as an artificial reef. It is known that some fish can cause much struc- 

 tural damage. Sharks can bite through metal cables in the process of 

 "testing" their teeth, and certain types of fish have solid plates for 

 lips and cause much damage while grazing. ^^ Invertebrates such as star- 

 fish can grind holes on various surfaces. 



ANTIFOULING COATINGS 



There are four approaches in the use of biocidal layers to prevent 

 sea-growth fouling: (1) coatings, (2) sheet materials, (3) impregnates, 

 and (4) toxic metal sheathing. These materials and approaches are dis- 

 cussed in descending order of their frequency of use. 



Coatings 



Antifouling coatings can be categorized as those containing: (1) low 

 toxicity ingredients, such as cuprous oxide; (2) medium toxicity ingredi- 

 ents, such as organotin; and (3) high toxicity ingredients, such as arsenic, 



1 A A 77-79 



lead, and mercury. 



Cuprous oxide paints are established materials with a long history of 

 excellent performance, have little known adverse effect on the marine 

 ecology, and are widely available as commercial formulae or specification 

 paints . 



Organotin-containing paints are at least as effective as copper-based 

 paints in most uses. However, because organotins are more toxic to marine 

 creatures and man than inorganic copper compounds, they require greater 

 care and expense in application, removal, and disposal. ^"^ Environmental 

 considerations of these materials in the marine ecosphere are under study. 



Antifouling paints have been made with other antifoulants . Restric- 

 tions on their application result from their toxicity to humans and effects 

 on the marine environment. Very toxic, although highly effective, paints. 



31 



