The interplay of sediment characteristics, depth, water temperature, and ocean currents shaping the biogeography of lancelets (Subphylum Cephalochordata) in the NW Pacific waters

Abstract

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 finescale biogeography of five species of lancelets (Asymmetron lucayanum, Branchiostoma belcheri, Branchiostoma japonicum, Epigonichthys cultellus, and Epigonichthys 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 Kuroshio 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 China, where the salinity is lower in winter because of the China 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 Northern Taiwan and the Taiwan Banks. Epigonichthys cultellus was found only at the Taiwan Banks, which had deep water, coarse sand, and a negligible amount of suspended sediments.

Evolutionary history of the extant amphioxus lineage with shallow-branching diversification

“…of preanal finboxesNo. of gonads Em @Taiwan #115.2663203425 Em @Taiwan #229.0672943223 Em @Taiwan #323.06730825NA Em @Taiwan #424.06728832NA Em @Taiwan #526.06631236NA Em @Taiwan #615.46829329NA Em @Taiwan #714.16930325?NA Em @Taiwan #813.35829220NAmean ± s.d.20.00 ± 5.7766.0 ± 3.2301.3 ± 10.629.7 ± 5.1 (n = 7) Ec @China #115.651222NANA Ec @China #214.147228NANA E sp@Kyushu #130.046202NA11 E sp@Kyushu #2NA50+2302015 Em , assigned to Epigonichthys maldivensis 16 ; Ec , assigned to E. cultellus 17 . Mean ± s.d.…”

“…Around Kuroshima Island, Okinawa, Japan, A. lucayanum and E. maldivensis have been reported as occurring sympatrically, and the Kuroshima A. lucayanum population has been suggested to contain two cryptic species 3 , 4 . In Taiwan, A. lucayanum and E. maldivensis are sympatric in most habitats as seen at Kuroshima Island 14 , 16 . Epigonichthys cultellus has been reported from the northern South China Sea 16 , 18 – 20 .…”

“…In Taiwan, A. lucayanum and E. maldivensis are sympatric in most habitats as seen at Kuroshima Island 14 , 16 . Epigonichthys cultellus has been reported from the northern South China Sea 16 , 18 – 20 . Although all of these amphioxus species with dextral gonads are distributed in tropical or subtropical waters, undescribed Epigonichthys -like amphioxus specimens were collected in this study from temperate Kyushu Island, Japan.…”

Iranian Branchiostoma species (Cephalochordata, Branchiostomatidae) inhabiting Chabahar Bay (Gulf of Oman), with remarks on habitat preferences

“…Globally, Branchiostoma and Asymmetron are found along the warm coasts of the world's oceans, while Epigonichthys is restricted to the coasts of the Indian Ocean and the western and central Pacific Ocean (Poss and Boschung, 1996;Lin et al, 2015). Locally, the sediment structure has been stated to determine the distribution of lancelets (Babu et al, 2013;Lin et al, 2015). B. arabiae and A. lucayanum in the western Persian Gulf have been found in areas where more than half of the sedimentary elements were larger than 0.5 mm (Futch and Dwinell, 1977).…”

“…Temperature, salinity, sediment characteristics (grain size, total organic matter), and ocean currents have been suggested as habitat preferences and geographical distribution factors affecting the population structure of lancelets (DaSilva et al, 2008;Lin et al, 2015). Globally, Branchiostoma and Asymmetron are found along the warm coasts of the world's oceans, whereas Epigonichthys is restricted to the coasts of the Indian Ocean and the western and central Pacific Ocean (Poss and Boschung, 1996).…”