IRG/COIPM INTERNATIONAL MARINE TEST - to determine the effect of timber substrate on the effectiveness of water-borne salt preservatives in sea-water. Progress Report 3: Report of first inspection of samples at Lae, Papua New Guinea
S M Cragg, C R Levy
Samples for the international marine test were placed on frames numbered I to VII. Frames numbered VII of both CCA and CCB trials are being stored dry in the laboratory at F.P.R. & D.C. Frames I to VI of both trials were suspended in the sea at Lae Harbour (Morobe Province, Papua New Guinea) on 6th December 1977. The first inspection of the CCA trial was carried out on 8th June 1978, at which time the samples in frame VI were removed and posted for microbiological examination, while frames V and VI were X-rayed. Due to the considerable discrepancy between the results of visual and of X-ray examination, it was decided that all frames should be X-rayed. Unfortunately, this could not be carried out until 22nd August 1978. At this time, the samples in frame IV of the CCB trial were removed and posted for microbiological examination. The samples were X-rayed on a Toshiba Rotanode. Best results were obtained by operating at 50 kV and 50 mA, and by using an exposure time of 0.16 s. X-ray pictures of the samples were examined and the degree of teredinid attack was given a rating from 0 to 3 (see IRG/WP/414). The loss of many of the control specimens can be attributed to extremely heavy teredinid attack. Indeed, in some cases, small teredinid-riddled traces of the samples remained. Specimens of Fagus sylvatica and Pinus sylvestris which were heavily attacked in June were missing by August. The X-rays of four samples made in June 6th are compared with those made on August 22nd and a particularly striking example of rapid attack in the period intervening between the two inspections is shown. Neither pholad nor crustacean attack was observed in any of the samples, which in June were attacked. There were no marked differences between the degree of fouling on different samples. In each case the fouling completely covered all surfaces, but did not project much from the sample blocks. A typical example of this fouling which is probably best described as grade 2 fouling (moderate) is shown. Bryzoans covered more surface area than the other fouling organisms. Other microscopic fouling organisms which were common were bivalves, hydrozoans and sponges. Insufficient information is available on the marine fauna of Papua New Guinea to enable a detailed description of the fouling community to be made.