Seasonal patterns of shell microincrement growth in a venerid bivalve Phacosoma japonicum were analyzed for the three populations from Hakodate, Ariake, and Kagoshima Bays around the Japanese coasts. The northernmost Hakodate population in Hokkaido grew rapidly in a limited interval between late spring and summer. The number of microincrements within an annual increment in the specimens from this population was smallest (200-250 increments) among the three samples of populations examined, and each microincrement width was largest (0.25-0.3 mm) at the central part of an annual increment By contrast, in the southernmost Kagoshima population in southern Kyushu, shell growth occurred slowly in a long term between early spring and fall. The specimens forming this population are characterized by having the narrowest microincrements (each 0.10 0.12 mm) and largest number of microincrements in the annual increment (300-350 increments). In this species, it has been confirmed that the growing season reflects the seasonal changes of phytoplankton abundance. The phytoplankton bloom usually occurs in spring in embayments of northern Japan and in summer in those of central and southern Japan. In Ariake Bay (central Kyushu), however, the phytoplankton becomes most abundant in winter and remains at low levels in the other seasons. The Ariake population of P. japonicum showed the most active growth in intervals between winter and early spring. In this sample, the microincrement width attained a maximum in the earlier portion of each annual increment, and the annual increment showed a particularly rightskewed pattern which reflects the winter phytoplankton bloom in this bay.
|出版ステータス||Published - 1997 12|
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