Larvae from deep-sea hydrothermal vents of Indian Ocean during 2018-2019

Abstract

The dispersal of life in isolated environment of hydrothermal vent is still remains questioned. Little is known about the distribution of meroplanktonic larvae in the watercolumn of hydrothermal vents. Here, we first provide evidence that meroplanktonic larvae may migrate thousands of meters above the ocean floor. The quantitative measures of mesozooplankton including meroplanktons were conducted in the Onnuri Vent Field(OVF), Solitaire Fields(SF), and reference-site(ref-site). The integrated abundance of mesozooplankton over the water column was relatively higher in the ref-site (77,037 inds. 100/m³) than vent sites (avg. 53,398 inds.100/m³). It was evident that majority of mesozooplankton was accumulated at 0-200 m. Mollusc larvae (gastropods and bivalves) appeared at all stations. Only one bivalve larvae that appeared at OVF and ref-site (0-200 m) was morphologically similar to Bathymodiolus spp. that inhabits in the hydrothermal vents. The gastropod larvae were morphologically identified as holoplanktonic and meroplanktonic larvae. 16 species of gastropod larvae was identified, and gastropod larvae species 1~4, 6, 13 had holoplanktonic feature (Atlanta, Oxygrus, and Limacina), while gastropod species 5, 7~12, 14~16 had meroplanktonic features. Gastropod larvae species 5, 11 and 12 only appeared at OVF, gastropod larvae species 9 and 10 only appeared in SF, while gastropod larvae species 14~16 appeared only at ref-site, and gastropod larvae species 7~8 appeared in all surveyed stations. Gastropod larvae species 5, 8, 12, 14 and 15 have similar morphological features of larvae of macrobenthic gastropod of Vetulonia spp. Gastropod larvae species 7 have morphological features similar to gastropods Lepetodrilidae, and species 9~11 and 16 have morphological features of Phymorphynchus protoconchs. The morphologically identified molluscs larvae of gastropods and bivalves in the upper layers of water column (0-200 m) indicates that larvae associated with the hydrothermal vents may disperse ~2,000 m above the vents.