Trophodynamics at the Longqi hydrothermal vent field and comparison with the East Scotia and Central Indian Ridges

Abstract

The Longqi vent field, situated on the Southwest Indian Ridge, is ecologically distinct among known hydrothermal vents fields. It hosts a combination of previously unknown species and those shared at species or genus level with other hydrothermal vents on the Central Indian Ridge (CIR) and East Scotia Ridge (ESR). We investigate the size-based and trophodynamics of consumers at Longqi vent field and compared these with ESR and CIR vent fields using stable isotope analysis. Intra-specific variability in δ13C and δ15N values in relationship to shell length was observed in Gigantopelta aegis but absent in Chrysomallon squamiferum. A model-based clustering approach identified four trophic groupings at Longqi: species with the lowest δ13C values being supported by carbon fixed via the Calvin–Benson–Bassham cycle, the highest δ13C values being supported by the reductive tricarboxylic acid cycle and intermediate values potentially supported by a mix of these primary production sources. These clusters were driven by potential differences in resource partitioning. There were also differences in the spread of stable isotope values at the vent field level when comparing Bayesian stable isotope ellipse areas among Longqi, CIR and ESR vent fields. This was driven by a combination of the range in δ13C value of macrofauna, and the negative δ15N values which were only observed at Longqi and CIR vent fields. Many of the shared species or genera showed inter-vent field differences in stable isotope values which may be related to site-specific differences in food sources, geochemistry or potential intra-field competition. This study provides important information on the trophic ecology of hydrothermal vent macrofauna found within an area of seabed that is licensed for seabed mining exploration.

Structure and Connectivity of Hydrothermal Vent Communities Along the Mid-Ocean Ridges in the West Indian Ocean: A Review

“…Few studies have investigated food web structures of macrofaunal communities in the Indian vents and reported that these communities possessed 2-4 trophic levels (Van Dover et al, 2001;Copley et al, 2016;Reid et al, 2020). These short trophic chains are typical of other vent communities [e.g., in the EPR (Gaudron et al, 2012;Reid et al, 2013), Juan de Fuca Ridge (Bergquist et al, 2007;Sweetman et al, 2013;Lelièvre et al, 2017), and MAR (Vereshchaka et al, 2000)].…”

“…The dominant macrofaunal species are typically symbiotic primary consumers. Unique stable isotope signatures and additional evidence from in situ hybridization and hologenomic analyses revealed that these dominant taxa rely heavily or exclusively on chemosymbionts for food, including C. squamiferum ( Van Dover, 2002;Goffredi et al, 2004;Nakagawa et al, 2014;Chen et al, 2015b;Reid et al, 2020), Gigantopelta aegis (Copley et al, 2016;Lan et al, 2021), Alviniconcha marissindica (Miyazaki et al, 2020;, R. kairei (Zbinden et al, 2008;Petersen et al, 2010;Guri et al, 2012;Jiang et al, 2020), and B. marisindicus (Yamanaka et al, 2003;McKiness and Cavanaugh, 2005;Copley et al, 2016). With the exception of C. squamiferum and G. aegis, symbiosis was known for congeneric species of these taxa in other oceans (Belkin et al, 1986;Stein et al, 1988;Endow and Ohta, 1989;Nelson et al, 1995;Rieley et al, 1999;Won et al, 2003).…”

“…Last but not least, how these structures vary in time and space is unclear. Furthermore, ontogenic shifts in diet were observed in vent arthropods both in the Indian Ocean and elsewhere ( Van Dover, 2002;Methou et al, 2020), and the microbial diet of several species varies across sites (Reid et al, 2020;Ma and Wang, 2021). However, the implications of these changes in food source on the ecology and adaptability of vent animals are still obscure.…”

Active hydrothermal vent ecosystems in the Indian Ocean are in need of protection

“…Geological or hydrodynamic barriers thus could be a more important determinant of connectivity between these vent communities than ridge characteristics such as spreading rate. The Longqi and Duanqiao populations share community components with the CIR, the MAR, and the East Scotia Ridge, and have been suggested to be a separate province (Zhou et al, 2018;Reid et al, 2020;Zhou et al, 2022). The northern SWIR vent Tiancheng would be part of the CIR-nSWIR province (Zhou et al, 2022).…”

“…However, some Indian-endemic species are thought to have low dispersal abilities due to negatively buoyant larvae or eggs, including the peltospirid snails Chrysomallon squamiferum, Gigantopelta aegis, Dracogyra subfuscus, and Lirapex politus (CR) (Chen et al, 2014), or the crab Kiwa sp. "SWIR" (Reid et al, 2020). Habitat degradation and fragmentation due to anthropogenic disturbance may lead to local loss of biodiversity (Pardini et al, 2017;van Dover et al, 2017;Niner et al, 2018) and ecosystem services (Le et al, 2017).…”