Vent Fauna on the Central Indian Ridge

Abstract

In deep-sea hydrothermal vent fields, faunal distribution is associated with the geochemical environments generated by hydrothermal vent activity. Hydrothermal vent fields on the Central Indian Ridge (CIR) are associated with vent fauna which is thought as a mixture of Atlantic and Pacific and are discretely distributed along the ridge axis of more than 1,000 km apart. In this chapter, faunal distribution in hydrothermal vent fields on the CIR is summarized at the intra-and inter-field levels. The species composition of the vent fauna in the four vent fields hitherto known is reviewed and updated, and faunal resemblance among the four vent fields of the CIR appears to reflect the number of species recorded, indicating that faunal surveys are not sufficient in describing the whole vent fauna on the CIR. All the genetic studies of the CIR vent fauna have indicated a high genetic connectivity among the local populations, despite the many potential dispersal barriers existing between the vent fields. On the basis of the spatial distribution of vent species in a vent field, typical vent fields on the CIR were classified into six zones, of which the central two zones are often covered by Rimicaris swarms in the Kairei and Edmond fields. The close relationship between vent fauna from the CIR and the western Pacific, compared to those from other regions, is highlighted. Knowledge of the Indian Ocean vent fauna is limited, and further quantitative information on the biodiversity of vent fauna will provide clues to the formation of biogeographical regions and the dispersal of vent fauna among deep-sea hydrothermal vent fields. Keywords

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

“…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 Ridge2202226; 17 to 43 taxa at Mid-Atlantic Ridge vent fields22527282930; 12 to 14 taxa at vents on the East Scotia Ridge3313233; see Supplementary Information for full details), providing confidence of adequate sampling at Longqi for comparative analysis in this study.…”

“…Our comparison of species on chimneys with contrasting levels of hydrothermal activity suggests that when activity wanes for an individual chimney, its fauna will follow a temporal succession that matches the spatial zonation around the vents. The low abundance of Rimicaris kairei on active vent chimneys at Longqi contrasts with the high-abundance aggregations of this species in the same environment at vents on the Central Indian Ridge202226, and the low abundance of Kiwa n. sp. “SWIR” close to vent fluid sources also contrasts with the aggregations of closely-related K. tyleri in the same location in zonation at vents on the East Scotia Ridge39.…”

“…Six species are previously known from vent fields on the Central Indian Ridge: the “scaly-foot” gastropod Chrysomallon squamiferum 19, the alvinocaridid shrimps Rimicaris kairei 20 and Mirocaris indica 20, the stalked barnacle Neolepas sp. 121, and the mussel Bathymodiolus marisindicus 20.…”

“…VG-2002”)22. A chiridotid holothurian has also been observed at vents on the Central Indian Ridge20, but specimens are not yet available for comparison with the Chiridota sp. found at Longqi.…”

“…Changes in the latitudinal range of the Antarctic Circumpolar Current, such as those inferred between 1.2 Ma and 650 ka, may have increased hydrographic isolation of the Southwest Indian Ridge from the East Scotia Ridge18, possibly contributing to the allopatric speciation of these taxa. A chiridotid holothurian has been reported at vents on the Central Indian Ridge20, and Chiridota hydrothermica is known at vents in the back-arc basins of the western Pacific and on the southern East Pacific Rise in similar distribution and abundance to the species at Longqi36, but further comparison is required to confirm the affinity of the species on the SW Indian Ridge.…”