Seasonal variation in sub-tropical Leucothoidae (Crustacea: Amphipoda) on Okinawa–jima, Japan

Commensal leucothoid amphipods make up a large component of coral reef ecosystems, yet little is known about their ecology. Monthly coral rubble samples were collected at Toguchi Beach and Sunabe Seawall on Okinawa–jima Island in the Ryukyu Archipelago between September 2010 and August 2011. Comparison of the numbers of leucothoid amphipods collected reveals a seasonal pattern. Numbers of Leucothoidae are highest in autumn and winter months, with members of the anamixid clade (genera Anamixis and Paranamixis) dominating samples in the autumn and members of the leucothoid clade (genus Leucothoe) dominating samples in the winter. This phase shift suggests that suitable sponge habitat is limited in the coral rubble. Leucothoid amphipods reproduce year round, yet the main reproductive period appears to occur in the autumn and winter months. Overall, the results indicate seasonal patterns and movement in Leucothoidae species.