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

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.

Two New Hot-Vent Peltospirid Snails (Gastropoda: Neomphalina) from Longqi Hydrothermal Field, Southwest Indian Ridge

“…Specifically, the peltospirids were found on chimney structures named "Tiamat" (Figure 1B; HOV Jiaolong Marker DFF11) and "Jabberwocky" (HOV Jiaolong Marker DFF1). Detailed location maps of each chimney within the Longqi vent field can be found in Copley et al (2016).…”

“…The Longqi hydrothermal vent field ( Figure 1A), the first active vent visually confirmed on the ridge, was initially discovered in 2007 using an autonomous underwater vehicle and a camera-grab system (Tao et al, 2012(Tao et al, , 2014. The earliest exploration of the site with a submersible was carried out on-board RRS James Cook expedition JC67 in 2011 using ROV Kiel6000 (Copley et al, 2016). Subsequently, the Chinese manned submersible HOV Jiaolong also visited the Longqi field on-board R/V Xiangyanghong 9 on several occasions (Zhou et al, 2017).…”

“…Up to this point, 21 megafauna species have been reported from the Longqi field (Copley et al, 2016). Among the dominant fauna of the Longqi field are two large snails in Peltospiridae, the scaly-foot gastropod Chrysomallon squamiferum Chen et al, 2015 and Gigantopelta aegis Chen et al, 2015 which often co-occur and form large aggregations side-by-side on diffuse flow venting areas (Chen et al, 2015a;Copley et al, 2016).…”

“…Among the dominant fauna of the Longqi field are two large snails in Peltospiridae, the scaly-foot gastropod Chrysomallon squamiferum Chen et al, 2015 and Gigantopelta aegis Chen et al, 2015 which often co-occur and form large aggregations side-by-side on diffuse flow venting areas (Chen et al, 2015a;Copley et al, 2016). Peltospiridae is one of three families in the gastropod clade Neomphalina, the other two being Melanodrymiidae and Neomphalidae (Heß et al, 2008).…”

“…Of the 11 currently recognised peltospirid genera, Chrysomallon and Gigantopelta are the only two that definitively rely on endosymbiotic bacteria for nutrition as adults (Chen et al, 2017; although Hirtopelta has also been reported to have endosymbionts in gill filaments; Beck, 2002), while most others are known to be deposit feeders and/or grazers (Fretter, 1989;Bouchet, 1989, 2001). Two other gastropods are reported from the Longqi field, including a Lepetodrilus species (Vetigastropoda: Lepetodrilidae) which is likely a grazer or filter-feeder and a species of Phymorhynchus (Neogastropoda: Raphitomidae) which is a carnivore/scavenger (Copley et al, 2016).…”