Nippon Suisan Gakkaishi 72 (4), 681-694 (2006)

Spatio-temporal differentiation of bivalve larval settlement sites in estuarine waters

RYOGEN NANBU,1 TOMOMI MIZUNO,2 TAKASHI KAWAKAMI,1 KAORU KUBOTA1 AND HIDEO SEKIGUCHI1

1Faculty of Bioresources, Mie University, Tsu, Mie 514-8507, 2Fisheries Research Division, Mie Prefectural Science and Technology Promotion Center, Suzuka, Mie 510-0243, Japan

Variations in the abundance of planktonic larvae and new settlers of bivalves were examined in the Kiso estuaries, central Japan, for 4 years from 2001 to 2004. Planktonic larvae and new settlers were mainly dominated by 4 bivalve species (i.e. Corbicula japonica, Ruditapes philippinarum, Mactra veneriformis, Musculista senhousia) showing marked seasonal and interannual variations in densities of each bivalve species: M. senhousia was most abundant in the planktonic larvae, whereas C. japonica was most abundant in the new settlers. This indicates that larval mortality until settlement may be highest in M. senhousia and lowest in C. japonica. It was concluded that there was no significant relationship between the abundance of planktonic larvae and new settlers. Spatio-temporally, larval settlement sites within the Kiso estuaries were different among these 4 bivalve species: C. japonica, common in the brackish water, settled mainly in the upper part of the estuaries, while the other 3 species settled mainly in the lower part (larval settlement site of each species was temporally not overlapped). A difference in salinity preference of the new settlers may drive the differentiation of larval settlement sites within the estuaries between C. japonica and the other 3 species: new settlers of C. japonica prefer less saline water, whereas those of the other 3 species prefer more saline waters.


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