Same (sea) bed different dreams: Biological community structure of the Haima seep reveals distinct biogeographic affinities

Abstract

<p>Deep-sea chemosynthetic communities, including hydrothermal vents and cold seeps, harbour hundreds of endemic species currently threatened by deep-sea mining and hydrocarbon extraction. The South China Sea (SCS), a semi-enclosed marginal sea with two well-investigated active seeps (Haima in the west and Site F in the east), provides an opportunity to understand the biogeography of chemosynthetic ecosystems. Here, we conducted extensive field surveys using Remotely Operated Vehicles (ROVs) and collected specimens for morphological observations, molecular barcoding, phylogenetic analysis, and stable isotope analysis. Cluster analyses were applied to reveal the community structure of vents and seeps in the Western Pacific and Northern Indian Ocean. A total of 65 species covering seven phyla and 14 classes have been identified from Haima, doubling the number of species reported previously. Among them, 35 species are currently known only from Haima. Stable isotope analysis shows a typical chemosynthesis-based biological community. Community structure analysis at the genus level clustered Haima with Site F, though the species compositions and dominance of two seeps are fairly distinct. Between the two active seeps in the SCS, the higher species richness and endemism at Haima are potentially due to multiple factors, including the unique environmental factors there and the geographic isolation in the northwestern corner of the SCS. Moreover, a similarity in community compositions at the genus level between seeps in the SCS and North Indian Ocean was revealed, potentially mediated by the Early Pliocene opening of the Indonesian islands and the strong westward Indonesia Throughflow. Given the ongoing gas hydrate exploration activities in the SCS, our results will contribute to establishing a global network of marine protected areas for chemosynthetic-based ecosystems. The rich and endemic biodiversity at Haima calls for policymakers to formulate regulations to conserve the unique biodiversity there.</p>

Scallop-bacteria symbiosis from the deep sea reveals strong genomic coupling in the absence of cellular integration

“…The thiotrophic symbionts of vesicomyids, bathymodiolines, and siboglinids encode complete dissimilatory nitrate reduction pathways to provide electron accepters and ammonia [ 6 , 24 , 74-76 , 79 ]. Our previous study found that the δ 15 N value of C. margaritatus (9.9‰) was substantially higher than those of clams, mussels, and tubeworms reliant on SOB for nutrients only [ 23 ]. Because our observation of the scallop showed that it had a full digestive gland ( Fig.…”

“…Catillopecten margaritatus —a deep-sea glass scallop that inhabits the Haima seep in the South China Sea— is commonly found on the empty shells of the vesicomyid Archivesica marissinica and around the tubeworm Sclerolinum annulatum aggregation [ 22-24 ]. Our previous analyses of the stable isotopes of C. margaritatus [ 23 ] revealed δ 13 C and δ 34 S values typical of the SOB symbiont-bearing bivalves that are known to rely solely or mainly on SOB for nutrition [ 12 , 23 , 25 ]. In this study, we aimed to characterize the chemosymbionts of C. margaritatus .…”

The genome of the deep-sea anemone Actinernus sp. contains a mega-array of ANTP-class homeobox genes

“…individuals were collected from the Haima cold seep in the South China Sea at a depth of 1386 m ( figure 1 a ), where Actinernus sp. was commonly observed on the shells of the deep-sea clam Archivesica marissinica around cold-seep mussel beds [ 20 , 25 , 26 ]. The genome of Actinernus sp.…”

Hydrothermal vent fauna of the western Pacific Ocean: Distribution patterns and biogeographic networks

“…A recent molecular study identifies a single widespread holothurian species shared with Indian Ocean vent fauna (Thomas, Sigwart, & Helyar, 2022) while He et al. (2023) report the Okinawa Trough Shinkaia crosnieri Baba and de Saint Laurent, 1992, at seeps in the Indian Ocean.…”