MEPS 310:95-108 (2006)  -  doi:10.3354/meps310095

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

Hidetaka Nomaki1,2,*, Petra Heinz3, Takeshi Nakatsuka4, Motohiro Shimanaga2, Naohiko Ohkouchi1, Nanako O. Ogawa1, Kazuhiro Kogure2, Eiko Ikemoto2, Hiroshi Kitazato1

1Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
2Ocean Research Institute, University of Tokyo, Minamidai 1-15-1, Nakano-ku 164-8639, Japan
3Institute of Geosciences, Sigwartstrasse 10, University of Tübingen, 72076 Tübingen, Germany
4Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-Ku, Sapporo 060-0819, Japan

ABSTRACT: 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 13C-labeled food materials. In this study, 3 different 13C-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 13C-labeled algae from the sedimentary organic matter. On the other hand, benthic foraminifera ingested 13C-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: Cyclammina 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.

KEY WORDS: Benthic foraminifera · Feeding ecology · In situ tracer experiment · Carbon budget · Deep-sea

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