The interplay of sediment characteristics, depth, water temperature, and ocean currents shaping the biogeography of lancelets ( S ubphylum C ephalochordata) in the NW P acific waters

Lancelets (or amphioxus) are often found within the soft bottom of shallow tropical and temperate seas. The present study is the first to provide a fine‐scale biogeography of five species of lancelets ( A symmetron lucayanum , B ranchiostoma belcheri , B ranchiostoma japonicum , E pigonichthys cultellus , and E pigonichthys maldivensis ) in the NW Pacific and examine the effects of multiple environmental parameters. From multivariate analyses, the distribution and abundance patterns of lancelets were explained by a combination of factors comprising depth, temperature of the collecting month, mean temperature of the coldest month in the year, medium particle size and silt/clay ratio of the sediments. In addition, ocean currents also affect their distribution range. The major occurrence of A . lucayanum and E . maldivensis was associated with the warm K uroshio current, but E . maldivensis exhibited higher tolerance to low salinity and low temperature, and preferred substrata of slightly larger grain size, a lower ratio of suspended sediments, and deeper water. The closely related B . belcheri and B . japonicum exhibited fine‐scale habitat differentiation, and B . japonicum was abundant along the southern coast of C hina, where the salinity is lower in winter because of the C hina Coastal Current and the substratum is composed of very coarse sand with suspended sediments. Branchiostoma belcheri occurred in low abundance and was only recorded in N orthern T aiwan and the T aiwan Banks. Epigonichthys cultellus was found only at the T aiwan Banks, which had deep water, coarse sand, and a negligible amount of suspended sediments.