Deep-sea sediment cores collected in April-May 1997 in the 10M pioneer area in the Clarion-Clipperton Fracture Zone of the NE Pacific were used to study vertical distribution patterns of meiobenthos (i.e., bottom-dwelling animals passing through an 0.5 mm mesh size sieve) in relation to vertical profiles of deep-sea sediment geotechnical properties (water content, grain size distribution, plasticity, shear strength). Both sets of profiles showed a characteristic inflection below 2.5~3 cm depth in the sediment, with the bulk of meiobenthos being concentrated above that depth and the geotechnical properties similarly changing sharply below 2.5~3 cm. It is. concluded that the extent of meiobenthic penetration of the sediment, under conditions of the abyssal environment, seems to depend primarily on the physical setting of the· sedimentary habitat. Consequently, when monitoring biological effects of anthropogenic impacts on the deep-sea floor and when identifying areas to be set aside as protected or reference zones, changes in the sediment geotechnical parameters should be taken into account.
The close coupling between sediment characteristics and the structure of benthic communities has for long been known and analysed in numerous studies (Giere, 1993; Gray. 1982; Rhoads. 1974). predominantly in the shelf, areas where most of the benthic. studies have been performed. This ample body of data: is in sharp contrast with the paucity of evidence obtained from the deep sea (Gage and Tyler. 1991). The scarcity of deep-sea data is still more disturbing in view of plans being made for manifold uses of the deep-sea benthic environment. such as for instance waste disposal (Angel and Rice. 1996; Young and Richardson. 1998) and· mineral resource mining (Thiel. 1992). These plans call for setting aside areas on the deep-sea floor to be treated as reference or protected zones (Anon 1984; Thiel. 1992).
