Rapid response of the giant protist xenophyophores (Foraminifera, Rhizaria) to organic matter supply at abyssal depths revealed by an in situ dual stable isotope labeling experiment

Abstract

Abstract The trophic ecology of xenophyophores (Foraminifera, Rhizaria) was examined during a 2-day in situ feeding experiment on the seafloor (water depths of 5370\xa0m) off the east coast of Torishima Island, Japan. Both 13C-labeled glucose (as an example of labile dissolved organic matter) and 15N-labeled diatoms (as an example of labile particulate organic matter sinking from the ocean surface) were supplied to the specimens captured in in-situ incubation cores using the manned submersible Shinkai 6500. We found that xenophyophores took up both dissolved and particulate organic matter during the 2 days of incubation in situ. The higher concentrations of 15N-labeled diatoms in the xenophyophores than in the surrounding sediments suggest efficient collection and use of food resources by xenophyophores, and may support their rapid growth. It is likely that the agglutinated test of xenophyophores, which forms a contorted plate-like structure with upper open fan-like and funnel-like elements, also contributes to their ability to collect phytodetritus derived from the ocean surface.