Community Structures of Meiobenthos in Hydrothermal Vent Sediment at the Pacific and the Indian Ocean

Abstract

Hydrothermal vent system is one of the important ecosystems with high productivity and biomass in the deep-sea. Meiobenthos, the sediment inhabited small sized benthic animal groups sieved with mesh aperture between 1 ㎜ and 32 ㎛, are very important in these ecosystems because of this extremely high density and diversity. The effect of hydrothermal activity on meiobenthic communities has not been described in detail. Only a few results of their community structure was reported, in the Sagami Bay (Shirayama, 1996), North Fiji Basin (Vanreusel et al., 2007) and Papua New Guinea (shallow water hydrothermal venting site; Zeppilli and Danovaro, 2009). In this study, the spatial patterns of meiobenthic communities in hydrothermal vent sediment were examined. Sediment samples for analyzing of meiobenthic community structure were collected using a submersible \\\\'Shinkai 6500\\\\', multiple corer, TV grab at 12 stations at six sites (the Rodriguez Triple Junction of Indian Ocean, Edison seamount site of Papua New Guinea, the Fiji Lau basin and the the Tonga basin in southwestern Pacific ocean) from 2002 to 2007. In all, 15 meiofauna groups were recorded. Nematodes were the most abundant taxon. Harpacticoid copepods, polychaetes, crustacean nauplii and benthic foraminiferans were also dominant groups at all sites. The total meiofauna density at the study sites varied from 49 to 419 ind./10 ㎠. Active hydrothermal sediments in the Edison seamount site of Papua New Guinea contain up to 150 harpacticoid copepods per 10 ㎠ of sediment. In a inactive ridge sediments, devoid of macrofaunal organisms, the abundance of harpacticoid copepods never exceeded 15 ind./10 ㎠. Multivariate analysis (multidimensional scaling) revealed significant differences in community structure among the three regions; near an active hydrothermal vent, in a inactive hydrothermal vent and adjacent typical deep-sea bed sites.