Vol. 62: 55-60, 1990
MARINE ECOLOGY PROGRESS SERIES
Published April 5
ABSTRACT: Results of recent models suggest that fecal pellet production by pelagic tunicates should have a major impact on the relative magnitude of export of particulate organic matter from the upper mixed layer of the ocean. However, little is known of the sinking velocities of feces from small salps and doliolids living in continental shelf waters. This study was designed to determine the sinking velocity of fecal pellets from Dolioletta gegenbauri under natural and amended food conditions, and to examine whether sinking behavior is best described by the Stokes or inertial formulations of the force balance equation. Still-water sinking velocity of pellets was determined in the laboratory at 20ºC and 36.0 %o S in a glass cylinder, and ranged from 59 to 405 m d ¬¹. Most of the feces produced by specimens fed only naturally occurring particles did not sink. About 70 % of the total variance of the logarithm of sinking velocity of the pellets produced by specimens fed the amended diet was explained by a linear regression against the logarithm of pellet volume. These pellets sank more slowly than was expected based on sinking velocities of the pellets of copepods, euphausiids and salps. Also, the rate of increase of sinking velocity with increasing pellet size (which was a linear function of diameter) was lower than predicted by the Stokes equation (i.e. where sinking velocity of spherical particles are directly proportional to the diam.²), indicating that the pellets fell in an intermediate zone between the Stokes and inertial forms of the force balance equation.