Polyurethane Foam. A specimen of soft and spongy polyurethane foam was 

 recovered with no visible deterioration caused by marine organisms, it was also not 

 affected in any way by the deep sea environment. Information on the manufacture 

 and application of polyurethane foam is presented in Reference 9. 



Polyethylene Foam. No visible deterioration caused by marine organisms 

 could be detected on the recovered semirigid polyethylene foam. However, the 

 specimen had decreased in dimension and had folded in two as a result of environ- 

 mental effects (Figure 41). The foam material did not return to its original dimension 

 and shape even after it had been dried. The reason for this could be that this foam 

 material is composed of closed cells and that these cells had ruptured when the foam 

 was lowered to the ocean floor, thereby permanently changing Its shape. 



It is possible that both of these plastic foam materials could be deteriorated 

 by marine borers if the materials were placed directly against wood bait pieces. 



Deep Ocean Borers 



The species of borers found in wood and plastic specimens have been identified 

 as Xylophaga washingtona Bartsch, a wood-boring Pholadidae. Other pholads related 

 to Xylophaga are the rock-borers such as Penitella , Zirfaea , and Borneo , and a wood- 

 borer, Martesia, which does considerable damage to waterfront structures. The 

 average growth rate of Xylophaga washingtona in wood panels was as follows: At 

 4 months, 1/32 Inch; at 6 months, 3/32 inch; at 13 months, 3/16 inch; at 24 months, 

 7/16 inch; and at 35 months, 1 l/l6 inch. Species of Xylophaga duplicata Knudsen 

 which were found together with Xylophaga washingtona in wood exposed at Test Site I 

 were not found in wood exposed at Test Site II. New species of these deep sea borers 

 were discovered in the wood panels and the description of these borers will be pub- 

 lished in the near future. 



The natural habitat, the life cycle of the adult borers, and the length of the 

 free-swimming stages of the larval forms remain a mystery. There are also many 

 other unanswered problems concerning the biology and distribution of this interesting 

 and destructive group of borers. Additional Information on Xylophaga washingtona 

 and Xylophaga duplicata is found in References 10 and 1 1 . 



Materials In Plastic Test Chamber 



The materials which were placed in the sterile plastic test chamber were 

 covered with fine bottom sediment, because the membrane filters used to seal the 

 ends of the tube had been ruptured either during descent or by marine animals at 

 the bottom. Some of the materials at the bottom of the tube were buried in this fine 

 sediment. Finding mud In the plastic tube was surprising, especially because the tube 

 was exposed about 4 feet above the sediment layer. This indicates that the bottom 

 waters, flowing at about 0.06 knot (data obtained with a current meter) at this 

 particular test site, are rather turbid. 



41 



