BIOLOGICAL REMOVAL OF FINE-GRAINED LITHOGENIC PARTICLES FROM A LARGE RIVER PLUME

The pelagic tunicate, Oikopleura dioica, feeds by non-selectively filt ering particles in the size range of 0.2-20 mu m. Tn the northern Gulf of Mexico, particulate matter in this size range contains large amoun ts of fine-grained lithogenic material because of the influence of the Mississippi River. During May 1992, O. dioica populations filtered be tween 2 and 44% (mean = 20%) of the upper 5 m each day. The filtered l ithogenic particles either remain in the oikopleurid house or are defe cated in fecal pellets which have high sinking velocities. Either way, the larvacean populations significantly alter the fates of fine-grain ed lithogenic particles in these waters and thereby enhance light pene tration. The widespread occurrence of oikopleurids in coastal regions of temperate and subtropical oceans suggests they could have a signifi cant influence on the fates of fine-grained lithogenic particles in di scharge plumes of many of the world's large, sediment-laden rivers.