Lallier, F. H. | Search bioRxiv

bioRxiv2025

Discovery of a chemosynthetic community at the serpentinite-hosted seep on the Quaker Seamount, Mariana Forearc

Deep-sea chemosynthesis-based ecosystems in the Mariana Region include hydrothermal vents on the Mariana Arc and in the Mariana Back-Arc, and serpentinite-hosted seeps on the Mariana Forearc - with the latter being by far the least studied. Here, we surveyed the biodiversity of the serpentine seep on the Quaker Seamount. At first glance, the area appears to be devoid of megafauna, but examination of the carbonates revealed dense aggregations of animals dominated by the limpets Bathyacmaea and Pyropelta on brucite-carbonate chimney structures exhibiting visible fluid venting. Sorting of recovered material yielded a total of 14 species and together with an observation of a Munidopsis squat lobster we report a total of 15 species; six of these are considered endemics of chemosynthetic ecosystems. The occurrence of taxa such as the snail Lurifax cf. japonicus and the limpet Pyropelta ryukyuensis, otherwise only known from distant vents in the Izu-Ogasawara Arc and Okinawa Trough off Japan, strengthens the hypothesis that serpentine seeps may function as dispersal stepping-stones across arc and back-arc systems.

ecology↗

bioRxiv2018

High rates of apoptosis visualized in the symbiont-bearing gills of deep-sea Bathymodiolus mussels

Symbiosis between Bathymodiolus and Gammaproteobacteria enables these deep-sea mussels to live in toxic environments like hydrothermal vents and cold seeps. The quantity of endosymbionts within the gill-bacteriocytes appears to vary according to the hosts environment. We investigated the hypothesis of a control of the endosymbionts density by apoptosis, a programmed cell death. We used fluorometric TUNEL-method and active Caspase-3-targeting antibodies to visualize and quantify apoptotic cells in mussel gills. To avoid artefacts due to depressurization upon specimen recovery from the deep-sea, we compared the apoptotic rates between mussels recovered unpressurised, versus mussels recovered in a pressure-maintaining device, in two species from hydrothermal vents on the Mid-Atlantic Ridge: Bathymodiolus azoricus and B. puteoserpentis. Our results show that pressurized recovery had no significant effect on the apoptotic rate in the gill filaments. Apoptotic levels were highest in the ciliated zone and in the circulating hemocytes, compared to the bacteriocyte zone. Apoptotic gill-cells in B. aff. boomerang from the pockmarks off the Gulf of Guinea, show similar distribution patterns. Deep-sea symbiotic mussels have much higher rates of apoptosis in their gills than the coastal mussel Mytilus edulis without chemolithoautotrophic symbionts. We discuss how apoptosis might be one of the mechanisms that contribute to the adaptation of deep-sea mussels to toxic environments and/or to symbiosis.

zoology↗