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The Settling and Growth of Wharf-pile Fauna in Port Nicholson, Wellington, New Zealand


The fouling of ships, wharf-piling, and similar structures by masses of marine animals and plants is not the outcome of a single event, but results from a long sequence of events culminating in the establishment of a complex community of larger animals and plants. If a clean piece of wood or metal is immersed in the sea, it is first occupied by the settling on it of larval stages of a variety of organisms, few of which are prominent in the final fouling community. These young individuals perish in great numbers, but some survive to grow and to form a pioneer community providing a new environment, which then shelters the young of other individuals, and so the community develops in numbers and variety, changing from one type of community to another until the slower-growing larger organisms settle and survive, producing at last the climax association, a fouling community which continues for many years.

The problem of preventing fouling is accordingly not primarily concerned with direct control of the actual fouling community, but should aim rather at preventing the establishment of pioneer communities. This paper records observations made at Queen's Wharf, Port Nicholson, over a thirteen-month period, using test blocks of oregon pine in such a way as to show the constituents of the pioneer communities, the periods in which the larval stages of these animals settle, and to give information on the nature of the early subsequent communities. These data also provide much information useful as a guide to studies on the life-histories and other aspects of these animals. The study also gives extensive data on the set and development of the wood-destroying marine organisms which are of considerable importance in the damage they do to immersed wooden structures.

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Test blocks of Oregon pine (Pseudotsuga taxifolia) were chosen because of its straight grain and its greater susceptibility to attack by borers than either Totara (Podocarpus totara) or other hard woods frequently used in wharf piles in this country. The use of Oregon has possibly permitted accelerated destruction by borers, but it is unlikely to have falsified appreciably the overall pattern of settling or growth. Each unit (Fig. 1) had two components 12 in. by 12 in. by 1½ in., with one component in the horizontal plane and the other in the vertical. The two were tied together by Tobin bronze wire, which is resistant to marine corrosion. Weights were attached to the bottom of the horizontal component, and the whole test block was suspended about 4 ft. below low-tide level. Two series of units
Fig. 1.—Diagram of test block.

Fig. 1.—Diagram of test block.

were used: firstly, a series of twelve "long term" blocks, all put down on 30th March, 1949. These were raised one each month till 30th April, 1950. Secondly, a series of eleven "short term" blocks, a single one of which was put down at the beginning of each month and raised at the end of the same month. As the first long-term block was down only one month, it also served as the first short-term block. Owing to various difficulties, it was not possible to raise blocks in December, 1949. These were raised at the end of January, 1950. The two-series system was used to demonstrate the monthly larval set (on the short-term blocks) and indicate page 3 how the monthly set was modified by animals already established on the long-term blocks. Allen and Ferguson Wood (1950) used a four-weekly series of glass plates in fouling experiments in Australia, and they remark "it is generally at this stage (i.e., four weeks) that the greatest number of specimens are present. Further immersion results in the elimination of many of these, however, particularly in the period three to six months after setting." This is very true in the present experiment, and we have reason to believe a climax association had not been reached on the test blocks even after thirteen months.

We have used diagrammatic presentation of the monthly temperature records to demonstrate the temperature distribution for the month more fully than does the simple graph of average temperatures. The vertical base line of the triangle (Figs. 2 and 3) gives the highest and lowest temperature for the month, and the apex represents the temperature that was most frequently recorded for the month and the number of times it occurred for that month. Thus, not only the highest and lowest temperatures for the month are shown, but also the distribution of daily temperature relative to the two extremes.

The authors wish to extend their thanks to the Wellington Harbour Board, for allowing us ready access to the Queen's Wharf, and to the Harbour Board Engineer, Mr. Hutchinson, for giving us valued assistance in the project; to Mr. P. McLean, the custodian of the Te Aro Salt-water Baths, for his co-operation in taking daily temperature records throughout the period of the experiment; to the late Mr. C. Masters, of Watson Victor Ltd., Wellington, for willing help in taking X-ray photographs of the test blocks; to Professor L. R. Richardson, for helpful advice and assistance; to Miss Beryl Brewin, Dr. D. Brown, Miss S. Jonathan (University of Otago, Dunedin), and Mr. G. Knox (Canterbury University College, Christchurch), and to Miss V. Dellow (Victoria University College), for identifying respectively the Ascidians, Polyzoa, Sponges, Polychaetes, and Algae.