浮遊期シズクガイの成長と分布(予報)
1988 年 1988 巻 33-34 号 p. 17-24
詳細
1988 年 1988 巻 33-34 号 p. 17-24
IMABAYASHI, HIROMICHI and TERUYOSHI IWATANI (Faculty of Applied Biological Science, Hiroshima University), 1988, Growth and distribution in planktonic larvae of the small bivalve Theora lubrica (Preliminary report). Benthos Research (Bull. Jap. Assoc. Benthology). 33/34, 17-24 Planktonic larvae of the samll semelid bivalve Theora lubyica, which developed from demersal eggs of approximately 60μm diameter, were reared at a water temperature of 12-25°C. The larvae grew linearly and the rate of growth increased with water temperature; 2.3μm/day at 12°C, 5.8μm/ day at 15°C and 7.8-12.5μm/day at 20°C. The size of first settled bivalve varied largely in shell length from 187.5 to 245.0μm (mean: 214.6μm). At a shallow waters where benthic bivalves were predominantly inhabited but disappeared almost in late summer (IMABAYASHI & TSUKUDA 1984), planktonic larvae after umbonal stage (shell length: 125μm) were collected more than 100 shell/m3 during a year and showed a maximum density of 7, 344 shell/m3 in spring. The diurnal investigation showed that the larvae were always concentrated near soft-muddy sediment and formed a small aggregation which migrated horizontally according to tidal current (maximum velocity: 19 cm/sec). Hence it is due mainly to the migration of aggregated larvae that the large settlemet occurs at suitable nursery ground.
