Degradation of discarded appendicularian houses by oncaeid copepods

Abstract

AbstractWe examined the degradation of discarded appendicularian houses due to feeding by oncaeid copepods in surface waters of the Kuroshio region. Vertical distributions of oncaeid copepods and discarded houses were investigated by optical sampling using a video plankton recorder (VPR). In situ VPR observations revealed that oncaeid copepods were commonly associated with discarded houses: the proportion of individuals attached to discarded houses reached saturated values of 25‐39% at house concentrations above 2000 houses m−3, suggesting that feeding by oncaeids was not limited by encounters at house concentrations typically observed in the upper 50 m. Laboratory observations confirmed that oncaeid copepods attached to the surface of discarded houses and ingested both house membranes and adhering particles. Individual feeding rates of the dominant Oncaea species, O. venusta and O. media, determined by measuring fecal pellet production and assimilation efficiency, varied from 0.13 μg C ind.−1 d−1 to 1.3 μg C ind.−1 d−1 (10‐37% body C d−1). Our results indicate that the oncaeid copepod community consumed up to 10% of house biomass each day in the upper 100 m of the water column, and show that through their close trophic coupling with discarded appendicularian houses, the oncaeids contribute significantly to house degradation in surface waters.