Productivity and grazing impact of Oikopleura dioica (Tunicata, Appendicularia) in Tokyo Bay

To estimate the productivity and grazing impact of a common appendicularian species Oikopleura dioica in Tokyo Bay, monthly observations on its abundance and vertical distribution were conducted during 2000. The abundance peaked in February and October, but was low during summer. Seasonal fluctuations in productivity were similar to those of the abundance, with maximum values of 92, 134 and 508 mg C m(-2) day(-1) for somatic, new house and discarded house productivity in October and 206 mg C m(-2) day(-1) for fecal pellet productivity in February, respectively. The averaged biomass of O. dioica was only 2.5% of that of copepods; however, the secondary productivity of the former corresponded to 12.4% of the latter. Daily grazing impact on particulate organic carbon ranged from 0.05% to 5%, which is close to the impact by copepods. These results imply that in Tokyo Bay, where small copepods and jellyfish are abundant, O. dioica is an important component of the ecosystem because it bridges between small primary producers and higher consumers.