Distribution and Variability of the Meiobenthic Assemblages near the Korean Polymetallic Nodule Claim Area of the Clarion-Clipperton Fracture Zone (Subequatorial NE Pacific)

Abstract

This study was carried out as part of a baseline long-term environmental project in the proposed mining areas for an environmental impact assessment of future mining in the Clarion-Clipperton Fracture Zone (CCFZ). The community structure and distributional pattern of meiobenthos were investigated in the deep-sea bottom of the Clarion-Clipperton Fracture Zone of the northeastern Pacific in July 1998, 1999, 2001, 2003 and August 2004, 2005. Twenty one meiobenthic groups were found at the stations in the study area. The most abundant meiobenthos comprised nematodes followed by benthic foraminiferans and harpacticoid copepods. The maximum density of meiobenthos was 306 ind/10 cm(2) at the station located at 11A degrees N (water depth, 4833 m), and the minimum density was 6 ind/10 cm(2) at the station located at 14A degrees N (water depth, 5037 m). Oligotrophic conditions in the CCFZ seem to directly reflect the lower standing stocks of meiobenthos in the CCFZ compared to other deep-sea plains of similar depth. The latitudinal distribution pattern of meiobenthos in the study area seemed to be related with surface water primary productivity, which was connected to the water circulation pattern of the Pacific Ocean near the Equator, diverging at 8AN latitude and converging at 5A degrees N. The horizontal distribution of meiobenthic organisms in the study area showed high densities at the stations within 135-136A degrees W. The densities of meiobenthic organismas within the CCFZ were high at stations with few manganese nodules on the sediment surface at low-latitude sites. In 1998, the observed relative high values of meiobenthic abundance were at stations from 5A degrees to 6A degrees N. Other stations from 7A degrees to 10A degrees N showed no significant fluctuations during the interannual sampling periods. It is considered that the inter-annual fluctuation of meiobenthos abundance is intimately related with a regime shift that may have occurred in the north Pacific between 1998 and 1999, the El Nio period. Vertical distribution of meiobenthic organisms showed the highest individual numbers in the surface sediment layers of 0 similar to 2 cm depth and a steep decreasing trend as sediment becomes deeper at the stations of high latitude located in 16 similar to 17A degrees N. Size distribution analyses showed that organisms that fit into the sieve mesh size of 0.063 mm were abundant.