Molluscan Research 32(3): 159–176 ISSN 1323-5818 http://www.mapress.com/mr/ Magnolia Press Life history and population dynamics of the surf clam, Mactra veneriformis (Bivalvia: Mactridae), on an estuarine intertidal sandflat in western Kyushu, Japan TADASHI NAKANO1*, JUHN NASUDA1, YOSHIHIRO AGATA1, TATSUYA YURIMOTO2, YUKIO MAENO2, YASUO NAKAMURA3, FUMIHIKO YAMADA4 & AKIO TAMAKI5 1 Graduate School of Science and Technology, Nagasaki University, Bunkyo 1-14, Nagasaki 852-8521, Japan; 2 Japan Interna- tional Research Center for Agricultural Sciences, Tsukuba, Ibaraki 305-8686, Japan; 3 National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan; 4 Graduate School of Science and Technology, Kumamoto University, Kurokami 2- 39-1, Kumamoto 860-8555, Japan; 5 Graduate School of Fisheries Science and Environmental Studies, Bunkyo 1-14, Nagasaki 852-8521, Japan; *Corresponding author: E-mail:
[email protected] Abstract Mactra veneriformis occurs commonly on estuarine tidal flats in temperate East Asia. Based on population sampling and recording of environmental variables over an extensive sandflat at a river mouth in Ariake Sound, southern Japan for 39 months, several reproductive traits were monitored and the recruitment, growth, and survivorship for cohorts tracked. The reproductive season ranged from May to September. Each year three to five newly-recruited cohorts appeared in June to Octo- ber. A single cohort derived from adult spawning in late September occurred in December to January but disappeared by mid- May. Earlier summer recruits reached a maturation size in late September. Each year two or three cohorts survived until next February and fused into a composite cohort. High mortality in juveniles sometimes happened in the rainy period from June to July and at typhoon arrivals in July to October, with increased river discharges.