Displacement of Larger Foraminifera at the Western Slope of Motobu Peninsula (Okinawa, Japan)

Abstract

Abstract Living and death assemblages of selected benthic, symbiont-bearing foraminiferal species were compared at a NW-Pacific island slope. Two transects with different morphologies were chosen, one demonstrating decreasing, the other slightly increasing, steepness. Intensities of depth transport were estimated by measuring the differences between distribution parameters of living individuals and empty tests. Three factors were shown to induce depth transport: (1) traction caused by offshore bottom currents or the frequent tropical cyclones that cross the area, (2) slope steepness, and (3) differences in test buoyancies. Due to the depth position of living populations, the combination of these three factors leads to varying displacement intensities and mixing of empty foraminiferal tests. The two investigated larger foraminiferal species with porcelaneous tests living at the shallow slope—the rod-shaped Alveolinella quoyi (d'Orbigny) and the discoid Amphisorus hemprichii Ehrenberg—showed high buoyancy a...