日本海北陸地域産ハマグリ類の貝殻成長分析

抄録

High correlation between the shell growth and the sea-water temperature has been indicated based on the multiple regression analyses of daily growth increments and environmental factors, and on oxygen isotope analyses using fossil shells of Meretrix lamarcki, suggesting that shell growth analyses will be available for an investigation of palaeo-environmental change.
Geographical variations and chronological changes in shell growth in the Japan Sea were examined using fossil shells of Meretrix lusoria (Ruding) and Meretrix lamarcki DESHAYES collected from 4 localities of Holocene shell beds and from 4 stages of Jomon shellmound sites and compared with shell growth of recent specimens.
Average shell heights against absolute ages were calculated by Walford's graphic method. Specimens from northern localities generally had low initial shell heights and relatively high growth rates, while specimens from southern localities had relatively high initial shell heights and low growth rates. Samples of the Hokuriku area had medium values of the initial shell height and slightly low growth rates.
Growth of fossil shells of M. lusoria in the Hokuriku area was rapidder than that of recent specimens collected at the Hakata Bay and Ariake Sea. Daily growth increments of M. lusoria from Ariake Sea showed a tidal influence on shell growth, while the tide pattern did not appear in those from the Hokuriku area, suggesting that disturbance on shell growth during ebb tides had eliminated among shells of the Japan Sea where the tidal range is smaller than that of Ariake Sea. Changes in the shell growth during the Jomon transgression had a similar trend between specimens from the southern Kanto and the Japan Sea. Decrease of growth speed during the Middle Jomon period was recognized both in M. lusoria and M. lamarcki.