Spatial structures of hydrothermal vents and vent-associated megafauna in the back-arc basin system of the Okinawa Trough,western Pacific |
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Authors: | M Tokeshi |
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Institution: | (1) AMBL-Kyushu University, Reihoku, Amakusa Kumamoto, 863-2507, Japan |
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Abstract: | Spatial patterns and morphology of hydrothermal vents and the occurrence of vent-associated megafauna were investigated in
the back-arc basin system of the Okinawa Trough, western Pacific. Amongst hydrothermal vent fields located on the rising slopes
to the NE and S of the basin, the Iheya North area has been subjected to a series of intensive diving surveys. Hydrothermal
vents demonstrated concentrated patterns of distribution on different spatial scales. In Iheya North, the majority of vents
occurred in lines parallel to the NE to W/SW alignment of the spreading axis, within a radius of ca. 200 m around the most
active sulphide structure with the highest recorded fluid temperature of over 300°C. The morphology of hydrothermal vents
varied greatly from an incipient flat rock with crevices to a 20- to 30-m-tall, multi-flanged structure with concomitant variation
in the distribution and abundance of vent-associated megafauna, particularly a galatheid Shinkaia crosnieri and Bathymodiolus mussels. Comparison of active and inactive vents revealed that the spatial extent of Shinkaia ‘aggregation’ (a group of individuals with short nearest-neighbour distances) effectively defined a habitat unit of this
species, and active hydrothermal chimneys contained more of these units, leading to greater spatial occupancy by Shinkaia. Given the temporally unstable nature of vent structures as recognised by repeated surveys, vent assemblages are thought
to be closely dictated by the spatio-temporal dynamics of vents in the Okinawa Trough back-arc system. |
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