Natural fiber ropes such as cotton and Manila were placed on the bio-racks. 
One set of ropes was placed at the lower and another set at the upper section of the 
bio-racks. The ropes were held in place by interweaving them through the plastic 
specimens, and then tying them to the plastic specimens with a nylon parachute shroud 
line as shown in Figure 8. Other materials such as electrical conductors covered with 
0.015-inch-thick insulation over a No. 16 tin-coated copper wire, and plastic sheet 
materials were secured to the bio-racks. 
In order to expose the test materials to biological deterioration in sediment 
(where bacteria are found to be most active) as well as in water, the two bio-racks 
were attached to the STU frame so that the lower portion would be buried in the 
bottom sediment and the upper portion exposed to seawater about 3 feet above the 
mud line (Figure 9). 
Other materials placed on the STU for the biodeterioration study include single 
and multiconductor electrical cable materials (Figure 10), and 3 x 6.2-inch cylindrical 
concrete specimens (Figure 11). Coral concrete cylinders were selected for exposure 
because mollusks including Lithophaga, Gastrochaena, and Petricola are known to 
bore into dead coral or coral limestones. Living coral colonies are not attacked by 
the burrowing animals to the same extent as dead coral. There are waterfront as well 
as nonwaterfront structures made of coral concrete on the island of Guam, The list 
of materials placed on STU I-1 for the biological deterioration study is presented in 
the Appendix. Additional information about these materials are given in the Appendix. 
Materials containing antifouling paints or other toxic substances were excluded 
from exposure aboard the STU. The current velocity at a depth of 5,300 feet was not 
great enough (less than 0.5 knot) to carry away any toxic substance which might alter 
the natural biological fauna found in the immediate vicinity of the STU. 
RESULTS 
Marine Growth on STU Complex 
A report on the method used to emplace STU I-1 complex on the ocean floor in 
5,300 feet of water is presented in Reference 11. The sketch of the complex is shown 
in Figure 12, The subsurface gasoline-filled rubber buoy, the instrument package 
attached to the riser line, and the 1-inch-diameter twisted polypropylene riser line 
were lost sometime during the 35-month exposure period. 
The STU was retrieved by a grappling operation from aboard the USS Chickasaw, 
a fleet tug. The grappling hook snagged the nylon line and the chain which were 
stretched across the ocean floor and connected to the upper section of the STU frame. 
The recovered section of the polypropylene rope used as an inverted catenary 
line had a dense hydroid growth. Some of the hydroids were about 5 inches long. 
Slimy bacterial growth, annelid worms, white starfish, and actinarians (sea~anemones) 
