Different ingestion patterns of C-13-labeled bacteria and algae by deep-sea benthic foraminifera

Benthic foraminiferal food sources were examined in the central part of Sagami Bay, Japan (water depth 1450 m) based on an in situ feeding experiment with C-13-labeled food materials. In this study, 3 different C-13-labeled food materials were used: the unicellular marine algae Dunaliella tertiolecta, the marine diatom Chaetoceros sociale, and the marine bacterium Vibrio alginolyticus. The first two are representatives of phytodetritus and the third of organic matter produced in the sediments. Each type of food material was injected into a series of in situ culture cores and incubated for up to 21 d. We observed that some benthic foraminiferal species selectively ingested C-13-labeled algae from the sedimentary organic matter. On the other hand, benthic foraminifera ingested C-13-labeled bacteria unselectively from sedimentary organic matter. Total benthic foraminifera assimilated 8.8 mg C m(-2) d(-1) of sedimentary organic matter without phytodetritus assimilation. Based on the assimilation rates estimated in this experiment, we recognized 3 types of feeding strategy among deep-sea benthic foraminifera in Sagami Bay. There are those that ingest (1) fresh phytodetritus selectively (phytophagous species: Uvigerina akitaensis, Bolivina spissa, Bolivina pacifica); (2) fresh phytodetritus selectively but sedimentary organic matter as well when phytodetritus is absent (seasonal-phytophagous species: Bulimina aculeata, Textularia kattegatensis, Globobulimina affinis); and (3) sedimentary organic matter at random (deposit feeders: Cyclammind cancellata, Chilostomella ovoidea). These different types of carbon utilization should be considered not only for understanding modern ecosystems on the deep-sea floor but also for paleoceanographic reconstructions using the abundance and distribution, or isotopic composition, of benthic foraminifera.