[M-IS21] Chemosynthetic community and mud volcano: biology, geochemistry, and geophysics of fluid discharge

[MIS21-04] Could listening underwater sounds reveal the dynamics of chemosynthetic ecosystems?

★Invited Papers

*Tzu-Hao Lin¹, Chong Chen², Hiromi Kayama Watanabe², Shinsuke Kawagucci², Yung-Che Tseng³ (1.Biodiversity Research Center, Academia Sinica, 2.X-STAR, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3.Marine Research Station, Institute of Cellular and organismic Biology, Academia Sinica)

Keywords:Ecoacoustics, Underwater acoustics, Hydrothermal vents

Chemosynthesis-based ecosystems support unique communities fed by chemical energy generated from subsurface geological and microbial processes. Hydrothermal vents are the best-known of such ecosystems, often occurring along active ocean ridges, seamounts, and back-arc basins. Active geological activities produce low-frequency sounds, which can propagate a long distance underwater. Such signals likely serve as acoustic signposts for deep-sea larvae to remotely locate these isolated, island-like geological hotspots among the vast abyssal plain – as has been demonstrated in previous experiments associated with the settlement of coral, mollusk, and reef-associated fish larvae in shallow-water habitats. As such, habitat-specific soundscapes, a composite of sounds from geophysical and biological sources, may be key to maintaining the resilience of vent ecosystems, as they are threatened by fast-approaching deep-sea mining. Although the heterogeneity of underwater soundscapes has begun to gain attraction as a useful proxy of habitat quality and biodiversity, soundscapes of hot vents remain poorly studied. Here, we review modern techniques of soundscape-based ecosystem sensing and then discuss the applications in monitoring vents dynamics. We also investigate the uniqueness of vent soundscapes by using two new recordings, one from a deep-sea vent in Suiyo Seamount, Izu-Bonin Arc, and another from a shallow-water vent at Guishan Island, northeastern Taiwan. Both fields are dominated by low-frequency sounds generated from vent orifices. The observed spectral pattern is entirely different from soundscapes recorded at estuaries, coral reefs, continental shelves, and other deep-sea habitats. Our results support the hypothesis that hydrothermal vents are acoustically different from other habitats, but many questions remain open. For example, do different vents possess different acoustic characteristics? Can we predict the amount of fluid discharge and temperature by measuring the intensities of vent-associated sounds? How do these low-frequency sounds propagate across the surrounding three-dimensional terrain that varies from vent to vent? Do vent-associated organisms produce sounds, and how frequently do they vocalize? Answer these questions will require future, more detailed acoustic assessments of the dynamics of vents and their associated communities. Based on the experience in shallow-water marine ecosystems, soundscape-based ecosystem assessments can reveal the interactions between a biological community and its habitat, as well as the ecological impacts due to anthropogenic development. We believe the same approach will improve our knowledge of the ecological dynamics of hydrothermal vents. Beyond that, additional data from cold seeps and organic falls will also help evaluate the feasibility of using soundscapes in monitoring other chemosynthesis-based ecosystems.