Meiobenthic distribution and nematode community in hydrothermal vent area and adjacent deep-sea bed on the southern Lau back-arc basin

Abstract

This study was conducted to investigate the community structure and distributional pattern of hydrothermal and adjacent deep-sea meiobenthos and nematodes at the hydrothermal vent field sites of spreading axis and arc of the Lau Basin located southern part of Tonga islands. Qualitative Sampling were carried out by 3 dives of ROV MAGNUM (RV ARAON) and ROPOS (RV SONNE) using the suction sampler and TV grab (RV SONNE) at 7 stations of study sites in March 2011 and February 2012. Quantitative samples were collected using the multiple corer (11 stations) and push corer of ROV (2 stations). In all, 10 meiofauna taxa (3-7 taxa at each station) were found. Nematodes were the most abundant taxon (14~96%). Harpacticoid copepods (3~57%), crustacean nauplius (3~29%) were also dominant groups at all sites. The total meiobenthos density varied from 7 to 191 ind./10cm2 and biomass were 5~188 &micro g/10cm2 at each station. The sediments beneath the chimney mound of active hydrothermal vent contain up to 30 harpacticoid copepods per 10cm2 of sediment. In a inactive ridge sediments, the abundance of harpacticoid copepods never exceeded 15 ind./10cm2. Distribution of meiobenthic animal in adjacent deep-sea bed showed high densities at the stations within the caldera of seamount. Vertical distribution of meiobenthic animals showed the highest individual numbers in the surface sediment layers of 0~1cm depth and more steep decreasing treed southern part of Tonga islands. Qualitative Sampling were carried out by 3 dives of ROV MAGNUM (RV ARAON) and ROPOS (RV SONNE) using the suction sampler and TV grab (RV SONNE) at 7 stations of study sites in March 2011 and February 2012. Quantitative samples were collected using the multiple corer (11 stations) and push corer of ROV (2 stations). In all, 10 meiofauna taxa (3-7 taxa at each station) were found. Nematodes were the most abundant taxon (14~96%). Harpacticoid copepods (3~57%), crustacean nauplius (3~29%) were also dominant groups at all sites. The total meiobenthos density varied from 7 to 191 ind./10cm2 and biomass were 5~188 &micro g/10cm2 at each station. The sediments beneath the chimney mound of active hydrothermal vent contain up to 30 harpacticoid copepods per 10cm2 of sediment. In a inactive ridge sediments, the abundance of harpacticoid copepods never exceeded 15 ind./10cm2. Distribution of meiobenthic animal in adjacent deep-sea bed showed high densities at the stations within the caldera of seamount. Vertical distribution of meiobenthic animals showed the highest individual numbers in the surface sediment layers of 0~1cm depth and more steep decreasing tre