The next organisms to settle in this bacterial film are the single celled 

 algae. Diatoms such as the chain forming diatom Skelotonema costatum . 

 live on and in the polysccharide matrix. These algae have been shown to 

 metabolize and degrade TEG? into less toxic chemical species such as 

 dibutyl- and monobutylin. This active component of the biofilm on the 

 painted surface may be essential to the subsequent settlement of bryozoans 

 (Stebbing, 1981; William Banta, personal communication) and barnacles by 

 reducing the concentration of the antifouling agent at the surface of the 

 biofilm. One source of the difference in release rates measured by the 

 U.S. Navy's in-situ measurements of release rate and the EEA/ASTM release 

 rate tests in the laboratory is the presence of the bacterial/algal 

 biofilm on the TBT treated Navy Ships and its absence in the laboratory 

 tests. 



The next stage of succession is the attraction and attachment of the 

 larval stages of multicellular plants (macrophytes) and animals producing 

 hard or calcarious exteriors. This stage exhibits a marked increase in 

 the surface roughness and drag on the painted hull. If the surface could 

 be kept free of the bacterial/algal film, the subsequent settlement might 

 be prevented by failure of the surface to attract the free swimming larvae 

 of the next biofouling stages. Fundamental questions which need to be 

 answered include the nature of the bacterial attachment and the mechanism 

 involved in its irreversibly. What is the role of the polysaccharide 

 slime as an attractant to subsequent settlement of other organisms? Is 

 the presence of the film facultative or obligatory? What is the 

 concentration gradient of TBI across the biofilm? What part of its 

 success as an antifouling agent is due to its effectiveness in suppressing 

 the initial biofilm and what part is due to direct toxicity to higher 

 phylogenetic taxa? If the attachment of the bacteria could be prevented, 

 would that be sufficient to prevent subsequent settlement of higher taxi? 



New toxicants now being developed are targeted at the bacterial/algal 

 biofilm. These include phenylmercuric oleate, barium metaborate, 

 2-4-isothiazolin-3-one and 4-5-dichloro-2-N-octyl-3 (2H) -isothiazodone 

 (Miller et al., 1980, 1982). The development of these new toxicants will 

 require the usual period of testing to determine if they produce toxic 

 effects on non-target species in the environment. 



Mitsubishi Heavy Industries in Japan is developing a non-toxic mechanical 

 removal system which operates continuously. In this system, electrolyzed 

 sea water and compressed air are released from a series of nozzles along 

 the ships bilges. The froth rises along the sides of the ship, 

 potentially disrupting the permanent settlement of the microbiota on the 

 surface of the hull. 



IV-54 



