First record of nudibranch mollusk Onchidoris muricata (O. F. Müller, 1776) (Mollusca, Gastropoda, Heterobranchia) in the Sea of Japan and its ephemeral population associated with unusual prey

Abstract

The nudibranch mollusk Onchidoris muricata known from boreal waters of the western Pacific, North American Pacific shore, and both coasts of the northern Atlantic was first recorded from the Sea of Japan (East Sea). This discovery extends its distribution range southwards along the Asian Pacific coast from cool temperate waters of Kamchatka and Kommander’s Islands to cool temperate sub-zone of the Sea of Japan. Three discovered populations in the northern Sea of Japan are confirmed to be conspecific with other Pacific and Atlantic populations of O. muricata because of external and radular morphology along with low interpopulation genetic variation (<3 %) found between studied COI gene sequences, while intraspecific distances between Onchidoris species range from 12.9 to 19.7 %. One of the discovered population constitutes an ephemeral settlement and is associated with the bryzoan Microporina articulata, an unusual prey for the Onchidorididae. Despite observing reproducing O. muricata adult individuals sheltered in M. articulata colonies, the nudibranch population remains unstable and became extinct within one season; however, it can be resurrected due to larvae migration from adjacent waters using ecological plasticity of this species as intrinsic resource for distribution area extension.