Ecology and biogeography of megafauna and macrofauna at the first known deep-sea hydrothermal vents on the ultraslow-spreading Southwest Indian Ridge.

J T Copley,W D K Reid,V E Nye,B D Wigham,V Hühnerbach,C J Sweeting,H Wiklund,L Marsh,A G Glover

doi:10.1038/srep39158

Abstract

The Southwest Indian Ridge is the longest section of very slow to ultraslow-spreading seafloor in the global mid-ocean ridge system, but the biogeography and ecology of its hydrothermal vent fauna are previously unknown. We collected 21 macro- and megafaunal taxa during the first Remotely Operated Vehicle dives to the Longqi vent field at 37° 47′S 49° 39′E, depth 2800 m. Six species are not yet known from other vents, while six other species are known from the Central Indian Ridge, and morphological and molecular analyses show that two further polychaete species are shared with vents beyond the Indian Ocean. Multivariate analysis of vent fauna across three oceans places Longqi in an Indian Ocean province of vent biogeography. Faunal zonation with increasing distance from vents is dominated by the gastropods Chrysomallon squamiferum and Gigantopelta aegis, mussel Bathymodiolus marisindicus, and Neolepas sp. stalked barnacle. Other taxa occur at lower abundance, in some cases contrasting with abundances at other vent fields, and δ13C and δ15N isotope values of species analysed from Longqi are similar to those of shared or related species elsewhere. This study provides baseline ecological observations prior to mineral exploration activities licensed at Longqi by the United Nations.

Highlights

The Southwest Indian Ridge is the longest section of very slow to ultraslow-spreading seafloor in the global mid-ocean ridge system, but the biogeography and ecology of its hydrothermal vent fauna are previously unknown
Longqi is ecologically distinct among known hydrothermal vent fields, hosting species not yet recorded from other locations, and known species in abundances that contrast with populations elsewhere
The species richness of 21 mega- and macrofaunal taxa in our samples is within the range of values for well-studied vent fields on neighbouring seafloor spreading centres (4 to 35 taxa at vent fields on the Central Indian Ridge2,20,22,26; 17 to 43 taxa at Mid-Atlantic Ridge vent fields2,25,27–30; 12 to 14 taxa at vents on the East Scotia Ridge[3,31,32,33]; see Supplementary Information for full details), providing confidence of adequate sampling at Longqi for comparative analysis in this study

Summary

Introduction

The Southwest Indian Ridge is the longest section of very slow to ultraslow-spreading seafloor in the global mid-ocean ridge system, but the biogeography and ecology of its hydrothermal vent fauna are previously unknown. The longevity of hydrothermal activity at individual vent fields correlates negatively with seafloor spreading rate: geochronology of sulfides indicates activity lasting for millennia at vent fields on the Mid-Atlantic Ridge[6], compared with decadal-scale activity at individual sites on the East Pacific Rise. These differences in the spacing and longevity of vent fields may contribute to differences in the composition and dynamics of vent fauna on different ridges[7,8]. Correspondence and requests for materials should be addressed to J.C.

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