福井県下における沿岸付着性汚損生物の生態研究

Abstract

Although a number of studies have been made on the general biology of barnacles, year-round field observations on the ecology of each species distinctly discriminated are rather scarce in Japan, except for a very few species. This paper deals with ecological observations on four species of acorn barnacles, which are representative of the most harmful fouling organisms along the coast of Otomi in Uchiura Bay, situated on the southwestern part of the Japan Sea. These observations were made from December 1967 to September 1969. Planktonic larvae were sampled by vertical hauls of plankton-net (45cm in mouth aperture and 0.33mm in mesh size) from the bottom every two or three days, and every month the number of barnacles that settled on six kinds of colored celluloid plates (25.0×18.5cm or 30.5×21.0cm) suspended at various depths was counted. Results obtained are summarized as follows: 1) The most dominant species was Balanus trigonus DARWIN, followed by B. venustus DARWIN, B. eburneus GOULD, and B. improvisus DARWIN. The latter three species are apparently recent invaders from foreign countries with timbers on the cargo boats. 2) From observation on the occurrence of pelagic larvae and the barnacles settled on the celluloid plates, the breeding season of each species is assumed to be as follows: In B. trigonus it extends from late May to late July, and secondarily from early September to late November (water temperature showed 17 to 29°C at 1 meter depth) with the peak in late May to late June (18 to 24°C); In B. venustus from late April to late June (14 to 22°C) with the peak in June (18 to 22°C); B. eburneus in July and September (21 to 29°C); B. improvisus from late October to late November and again from early March to late June (14 to 22°C) with the peak in June (18 to 22°C) (Fig. 3). 3) Vertical distribution in the settlement of each barnacle from surface to 13 meter depths was as follows: B. trigonus was found most abundantly at 13 meter depth in June and at 5 meter depth in July, while B. venustus settled most abundantly at 13 meters and B. improvisus was fairly abundant at 1 meter, respectively. B. eburneus, on the other hand, was found to attach almost evenly throughout the range mentioned above (Fig. 4). 4) In general, these four species of acorn barnacles settled more abundantly on dark coloured plates such as black or blue than on those of light colours such as red, yellow, green or white (Table 1).