New distribution record of deep-sea mussel, Bathymodiolus aduloides (Mollusca: Bivalvia: Mytilidae) from a hydrothermal vent, Myojinsho

Abstract

From the deep-sea hydrothermal vents and cold seeps ecosystems, more than 600 species containing many endemic species have been discovered. The deep-sea mussels of the genus Bathymodiolus are dominant species at deep-sea hydrothermal vents and cold seeps throughout the world. They are known to rely on the nutrients produced by the chemosynthetic symbiont in their gills. In 2009, we found a colony of bathymodiolin mussels at a hydrothermal vent of Myojinsho (Myojin Reef), which is a hardly investigated area. Myojinsho lies in the northern segment of the Izu-Ogasawara (Bonin) Arc and had been volcanically active until recently. We collected specimens from the colony using a remotely operated vehicle. We identified them as Bathymodiolus aduloides by morphological observation and phylogenetic analyses using mitochondrial DNA sequencing. We could not find any other species of mussels during the dive. This result is interesting because this species has not been discovered from hydrothermal vents in this region; the dominant species in this region, including the neighbouring Myojin Knoll Caldera, is B. septemdierum.

Deepest and hottest hydrothermal activity in the Okinawa Trough: the Yokosuka site at Yaeyama Knoll

“…No other Bathymodiolus species were found to inhabit the Yokosuka site, although more thorough exploration in the future may recover other species. The dominance of B. aduloides is nevertheless of interest because at all other OT vents it is never present in high abundance [ 89 ]), the dominant species being B. platifrons and B. japonicus . Perhaps, the fact that B. aduloides host sulfur-oxidizing endosymbiont (as opposed to methane-oxidizers in B. platifrons and B. japonicus [ 89 ]) contributes to its dominance in the Yokosuka site, but this is largely speculative at this point.…”

“…No other Bathymodiolus species were found to inhabit the Yokosuka site, although more thorough exploration in the future may recover other species. The dominance of B. aduloides is nevertheless of interest because at all other OT vents it is never present in high abundance [89]), the dominant species being B. platifrons and B. japonicus.…”

“…japonicus. Perhaps, the fact that B. aduloides host sulfur-oxidizing endosymbiont (as opposed to methane-oxidizers in B. platifrons and B. japonicus [89]) contributes to its dominance in the Yokosuka site, but this is largely speculative at this point. Alaysia sp.…”

Dispersal Ability and Environmental Adaptability of Deep-Sea Mussels <i>Bathymodiolus</i> (Mytilidae: Bathymodiolinae)

“…32 zone of the Nansei-shoto Trench, and vents of the Okinawa Trough (however, our genetic analyses have not confirmed its existence in the Nankai Trough). Some B. aduloides specimens have been obtained so far from vents in the Izu-Ogasawara Island-arc [25].…”

On the presence of the deep-water mytilid Gigantidas horikoshii (Bivalvia: Mytilidae) in Taiwanese waters

“…Although the genus Gigantidas has been recorded from the Western Pacific, Indian and Atlantic Oceans, most of these species have only been recently recognized and described (after 2003), as they live in deep-water habitats, often in infaunal or semi-infaunal communities in patchy distributions at either seeps or vents, and in some cases at both environments (Hashimoto & Yamane, 2005;Kyuno et al, 2009). Three Gigantidas species had been cited previously for Taiwan waters: Gigantidas platifrons (Hashimoto & Okutani, 1994), one of the most widely distributed bathymodioline mussels in the Western Pacific (Xu et al, 2019), Gigantidas securiformis (Okutani et al, 2003) known from seep sites at Kuroshima Knoll and Nankai Trough in Japan, and at Four Way Closure Ridge, south of Taiwan, and Gigantidas taiwanensis (Cosel, 2008) only found between 200-350 m depth in a hydrothermal vent area on the Tashi fishing grounds at Kueishan Island, NE Taiwan (Cosel, 2008;Kuo et al, 2019).…”