Assessment of postmortem transportation of modern benthic foraminifera of the Washington continental shelf

A linear regression equation was used to estimate the traction velocity for each of the 31 most common benthic foraminiferal species in surface sediments of the Washington continental shelf. Using Scheffé's method of multiple comparisons, the traction velocities of these species were compared individually and by groups in order to detect species that would be transported in the same statistical population. Three traction-velocity groups were recognized: 1) four species with roughly equidimensional tests and low traction velocities; 2) 19 species with elongate, inflated or coiled, moderately inflated tests and intermediate traction velocities; and 3) eight species with elongate, highly compressed or coiled, discoidal tests and high traction velocities. Depending upon the bottom-current velocity, one of these three traction-velocity groups might be expected to numerically dominate a current-sorted assemblage. However, each major faunal association, defined by cluster analysis in the preceding paper, is composed of mixtures from all three groups. Direct observations of bottom currents suggest that velocities at the sediment-water interface are generally too low, with directions too erratic to effectively sort species identified in this study. Hence, faunal assemblages appear to be dominated by indigenous species whose distributions reflect the oceanographic and sedimentologic factors that limited living representatives.