Spatiotemporal changes in distributions of the two dominant bivalve species in an estuarine river connecting two brackish lakes, Japan

ABSTRACT

Spatiotemporal changes in the biomass and abundance of the two dominant bivalve species Corbicula japonica and Arcuatula senhousia were investigated at 14 stations positioned along the Ohashi River from November 2005 to August 2007. Corbicula japonica predominantly inhabited the upstream section of the primary branch and Kensaki stream of the Ohashi River, whereas A. senhousia predominantly inhabited the downstream section of the Ohashi River. However, the distributions were highly variable among stations and seasons. Intrusions of saline water from Lake Nakaumi varied with astronomical and climatological factors, and consequently, the halocline of the Ohashi River is subject to spatiotemporal changes. Changes in distributions of C. japonica and A. senhousia occurred in relation to a flood event, indicating that environmental disturbances affect the distributions of the two bivalve species. Responses of the two species to continual saline water intrusion were also observed during the period of normal flow conditions. We suggest that the distribution of the two species is closely related to the dynamics of the ambient saline water, which is the most important factor correlated to changes in the distributions of C. japonica and A. senhousia in the Ohashi River.

SUBJECT EDITOR:

• Sharon Hook

KEYWORDS:

• Benthic community
• disturbance
• estuarine ecosystem
• flood event
• saline water

Acknowledgements

The Shinji Lake Fishermen's Cooperative Association and Yu Ishitobi facilitated use of the laboratory for sorting benthos. Taeko Kimura, Kenji Toda and Hidenori Tanaka advised the authors on the identification of benthic species. The authors also wish to thank Akira Toi, Kensaku Nakamura, Kayoko Kunii, Kayoko Ogura, Mokuro Sato, Go Kawakami, Atsuko Nakano, Aika Nakano, Haruki Nishikori, Miyoshi Sato, Akiko Soga, Shigemi Kuwabara, Chie Okada, Mohit Chhetri, Kosuke Tsuji, Chisato Fujii, Shiho Ozaki, Yoko Yoshida, Chiharu Fukuhara and Hiroyuki Takata for their assistance in sampling, sorting, measurement and data input.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by PRO NATURA FOUNDATION JAPAN under grant Pro Natura Fund in 2005 and 2006; and the Ministry of Education, Culture, Sports, Science and Technology under grant KAKENHI 20681001.