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



Only one species of barnacle was recorded for the experiment—namely, Elminius modestus Darwin. A very heavy set showed on the May short-term block. A count of this block showed 25 animals to the square inch and an estimated total number of 17,750. Less heavy sets occurred in June and April, 1950 (Table I). In all page 10cases, the specimens were large enough to be clearly recognized as E. modestus. The barnacles were smaller on the vertical and silted areas of the blocks. The species made only erratic appearances on the long-term blocks, apparently because of failure to survive. At no time was E. modestus a very prominent feature of these blocks.

The heavy set during May and the moderately heavy set of June and April, 1950, suggest that the main spawning period of this species is autumn. Work overseas (Corlett, 1948) indicates that settling periods are determined to some extent by temperature. Temperature may not have been so great a factor in determining set in the present instance. For example, in months (October and November) with a temperature range approximating those months when E. modestus set heavily, no real indication of the expected set showed on the test blocks. Allen and Ferguson Wood (1950) state that Balanus trigonus and two varieties of B. amphitrite set fairly heavily from November to March, with smaller settlings in October and April to July. No monthly temperatures are given to allow comparison with E. modestus. E. modestus, on the short-term blocks, i.e., up to four weeks' growth, showed a diameter ranging from 1·0 mm. to 2·0 mm., with an average of 1·5 mm. By the end of the experiment, specimens up to 6·0 mm. in diameter were present on the long-term blocks, but no estimate of the age of these specimens can be given, as no information as to the settling date is available.