Nearest vent, dearest friend: biodiversity of Tiancheng vent field reveals cross-ridge similarities in the Indian Ocean.

Jin Sun,Chengjun Sun,Tong Wei,Yadong Zhou,Yick Hang Kwan,Yanan Sun,Yi Yang,Lei Yang,Ruiyan Zhang,Pei-Yuan Qian,Lingyun Qu,Xuyang Wang,Chong Chen

doi:10.1098/rsos.200110

Abstract

Biodiversity of hydrothermal vents in the Indian Ocean, particularly those on the Southwest Indian Ridge (SWIR), are still relatively poorly understood. The Tiancheng field on the SWIR was initially reported with only a low-temperature diffuse flow venting area, but here we report two new active areas, including a chimney emitting high-temperature vent fluids. Biological sampling in these new sites doubled the known megafauna and macrofauna richness reported from Tiancheng. Significantly, we found several iconic species, such as the scaly-foot snail and the first Alviniconcha population on the SWIR. Tiancheng shares a high proportion of taxa with vents on the Central Indian Ridge (CIR) and lacks a number of key taxa that characterize other vents investigated so far on the SWIR. Population genetics of the scaly-foot snail confirmed this, as the Tiancheng population was clustered with populations from the CIR, showing low connectivity with the Longqi field. Unlike the previously examined populations, scales of the Tiancheng scaly-foot snail were coated in zinc sulfide, although this results only from precipitation. The close connection between Tiancheng and CIR vents indicates that the dispersal barrier for vent endemic species is not the Rodriguez Triple Junction as previously suggested but the transformation faults between Tiancheng and Longqi, warranting further studies on deep currents in this area to resolve the key barrier, which has important implications for biological conservation.

Highlights

Since their initial discovery in 1977, deep-sea hydrothermal vents sustaining extremely lush biological communities for the deep ocean have attracted great attention from scientists and the general public alike [1]
Biological samples were collected from three venting sites in the Tiancheng vent field, located on the slope of the Tiancheng Seamount, i.e. the JL-87 diffuse flow area, the TC-2 diffuse flow area, and the Tiantang chimney with suction sampler by the remotely operated vehicle (ROV) Sea Dragon III during the China Ocean Mineral Resource R&D Association (COMRA) DY52nd cruise of R/V Dayangyihao in the Southwest Indian Ocean in April 2019
We presented a comprehensive account of the chemosynthesis-based megafaunal and macrofaunal community structure in the Tiancheng vent field, the easternmost active vent field currently confirmed on the Southwest Indian Ridge (SWIR)

Summary

Introduction

Since their initial discovery in 1977, deep-sea hydrothermal vents sustaining extremely lush biological communities for the deep ocean have attracted great attention from scientists and the general public alike [1]. Only nine active hydrothermal vent fields have been discovered in the Indian Ocean (figure 1a). The first vent was the Kairei field on the Central Indian Ridge (CIR) discovered in 2000, very close to the Rodrigues Triple Junction where three mid-ocean ridges meet [2]. From 2007 onwards, the Southwest Indian Ridge (SWIR) has been the focus of a number of research cruises resulting in the discovery of three active vent fields in two areas, with Longqi and Duanqiao fields in the western part and Tiancheng in the eastern part [7,8]. The third ridge, Southeast Indian Ridge (SEIR), has long been neglected with no active vents being visually confirmed, but the first one, Pelagia field, was found in 2017 [9]

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