Grazing impact on chromophoric dissolved organic matter (CDOM) by the larvacean Oikopleura dioica

Experiments were conducted to determine if the pelagic larvacean Oikopleura dioica could graze on chromophoric dissolved organic material (CDOM) and if so, could such grazing affect the optical characteristics of the water column. Although O. dioica was found to graze on CDOM, it also contributes to the CDOM pool. O. dioica cleared large, > 10 kDa CDOM, with clearance rates ranging from 0.5 ml d(-1) for humic material to 8.9 ml d-1 for proteins suggesting a differential cycling of dissolved organic material by this larvacean. Its excretion of CDOM was in the < 5 kDa size range. The clearance of large-sized CDOM (> 10 kDa) and the excretion of small-sized CDOM (< 5 kDa) resulted in an alteration of the molecular size distribution of the CDOM in natural seawater. Thus the relationship between grazing removal and excretion inputs will affect the cycling and molecular size distribution of CDOM and influence water color.