Coastal hypoxia is an increasing environmental concern affecting marine ecosystems worldwide, particularly impacting benthic organisms such as bivalves. While previous studies have focused on physiological responses of bivalves to hypoxic stress, the role of resident bacteria in their host's response to hypoxia remains poorly understood. This study investigated changes in resident bacterial communities of the ark shell Anadara kagoshimensis under hypoxic conditions, focusing on gill and hepatopancreas tissues.