Appendicularians in the southwestern Sea of Japan during the summer: Abundance and role as secondary producers

Abstract

Appendicularian abundance was investigated at a total of 235 stations over 5 years, from 2011 to 2015, in southwestern Sea of Japan to evaluate potential factors influencing abundance and to understand their effects on the marine ecosystem. Oikopleura longicauda was the dominant appendicularian species, present in 232 samples, and with the highest abundance (mean ± SD: 463 ± 694 individuals m '3) among the appendicularians. Warm conditions appear to favour O. longicauda based on a generalized linear model, and salinity and chlorophyll a concentration were not significantly related to abundance. The abundance of O. longicauda was correlated significantly with those of Microsetella and Oncaea, which are the grazers of discarded appendicularian houses, as well as that of carnivorous Sagitta. Oikopleura longicauda houses, discarded daily to the water column, were estimated to represent a carbon flux of 7.7 ± 7.8 mg C m '2 d '1 (mean ± SD), depending on their density and water temperature. We estimate that a minimum of approximately 13% of houses were consumed by Oncaea and Microsettela. Therefore, we suggest that secondary production by O. longicauda in the southwestern Sea of Japan increased during summer and leads to enriched production at higher trophic levels in the epipelagic ecosystem during this season.