From wood to vent: first cocculinid limpet associated with hydrothermal activity discovered in the Weddell Sea

Abstract

Lush ‘oases’ of life seen in chemosynthetic ecosystems such as hot vents and cold seeps represent rare, localized exceptions to the generally oligotrophic deep ocean floor. Organic falls, best known from sunken wood and whale carcasses, are additional sources of such oases. Kemp Caldera (59°42'S, 28°20'W) in the Weddell Sea exhibits active hydrothermal vents and a natural whale fall in close proximity, where an undescribed cocculinid limpet was found living in both types of chemosynthetic habitats. This represents the first member of the gastropod order Cocculinida discovered from hot vents, and also the first record from the Southern Ocean. Here, we applied an integrative taxonomy framework incorporating traditional dissection, electron microscopy, genetic sequencing and 3D anatomical reconstruction through synchrotron computed tomography in order to characterize this species. Together, our data revealed an unusual member of the genus Cocculina with a highly modified radula for feeding on bacterial film, described herein as Cocculina enigmadonta n. sp. Its phylogenetically derived position within the largely wood-inhabiting Cocculina indicates that it probably evolved from an ancestor adapted to living on sunken wood, providing a compelling case of the ‘stepping stone’ evolutionary trajectory from organic falls to seeps and vents.

Ecophysiology and ecological limits of symbiotrophic vesicomyid bivalves (Pliocardiinae) in the Southern Ocean

“…Experimental physiology studies have been conducted on several species in the group, in multiple oceans, with differing results. The metabolic rates that we recorded are broadly in line with expectations from similar species, including the epilithic Turneroconcha magnifica (formerly called Calyptogena magnifica) with rates approximately 1.6-6.3 (MO 2 : μmol O 2 g −1 h −1 , calculated using dry mass) (Arp et al 1984;Khripounoff et al 2017;Krylova and Sahling 2020), and two other smaller species of Calyptogena had lower rates of MO 2 (Childress and Mickel 1985).…”

“…The bivalve's siphons extended into the cold water for respiration, but the foot extends into warmer, anoxic, sulphide-or hydrocarbon-rich sediments to take up inorganic compounds such as hydrogen sulphide to supply endosymbiont microbes (e.g. Childress and Mickel 1985;Niemann et al 2009). Most pliocardiines occur in patches, from one to several square metres in suitable sediments (e.g.…”

“…In the Kemp Caldera A. s.l. puertodeseadoi was reported in several hard rock and soft sediment habitats (Linse et al 2019a) which dominant or visually distinct fauna comprised the seastar Paulasterias tyleri, the limpets Cocculina enigmadonta and Lepetodrilus concentricus, the pyconogonids Sericosura bamberi, S. curva, and S. dimorpha, and actinosolid anemones (Mah et al 2015;Linse et al 2019b;Chen and Linse 2020).…”

Integrative taxonomy of a new cocculinid limpet dominating the Aurora Vent Field in the central Arctic ocean

“…Cocculina aurora n. sp. was not found to be closely related with the only other cocculinid known to inhabit hydrothermal vent ecosystems, C. enigmadonta from the Southern Ocean [26]. This means the invasion of hydrothermal vent ecosystems occurred at least twice in Cocculinidae, independently.…”

“…Like C. enigmadonta [26], C. aurora n. sp. is also phylogenetically nested in a derived position within wood-fall specialist species, suggesting that it also used organic falls as evolutionary stepping-stones to adapt to living in hydrothermal vents.…”