Population dynamics of a hypoxia-tolerant bivalve: A comparison of two sites in the inner part of Ariake Bay, Japan

Abstract

Hypoxia-tolerant bivalve populations could be a key component of ecosystem function because of their predominance in hypoxic environments. In this study, we conducted field surveys at two sites to elucidate the biological traits of the hypoxia-tolerant bivalve Veremolpa micra. We detected new settlements at both sites during summer. More highly reduced conditions in the surface sediment were recorded at Site-A than at Site-B in August 2013. Following this hypoxic event, shell growth of V. micra at Site-A decelerated, whereas that at Site-B increased. The population density after recovery from the hypoxic event decreased more at Site-B than at Site-A. Body size exhibited very little growth at both sites during the fall and winter, but there was rapid growth during the subsequent spring and summer, with sexual maturity being reached in early summer. Our findings demonstrated that the growth rates and survival patterns of the hypoxia-tolerant bivalve populations differed between sites with different degrees of sediment reduction. To understand the biological traits of hypoxia-tolerant bivalve species, it is necessary to consider and evaluate spatial differences in hypoxic stress at the local site level.