Cycloclypeus carpenteri is the largest extant benthic foraminifer, dwelling in the deep eu-photic zone (a water depth between 60 and 130 m) of the warm oligotrophic Indo-West Pacific. This foraminifer harbors diatom endosymbionts and the foraminifer-microalgal association acts like a holo-biont. To verify that light is an important limiting factor controlling the vertical (depth) distribution of living Cycloclypeus holobionts, their physiological responses to light intensity were examined by short-term metabolic measurements and long-term incubations. Net oxygen production (OP) rates measured under different light levels using an oxygen microelectrode indicate that Cycloclypeus holobionts are daily net primary producers adapted to low light levels, with slight photoinhibition (reduced net OP rates relative to a light-saturated rate) over 100μmol photons m-2 s-1. Long-term growth increments of asexually reproduced juveniles incubated for two months at different light levels ranging from 0 to 100μmol photons m-2 s-1 show that Cycloclypeus holobionts are adapted to a low light level (～5μmol pho-tons m-2 s-1), but can be acclimatized to a certain low light ranges (<50μmol photons m-2 s-1). These ex-perimental results confirm that light is an important environmental gradient affecting the vertical dis-tribution of Cycloclypeus holobionts.

Department of Physics and Earth Sciences,University of the Ryukyus,Okinawa 903-0213,Japan;Tropical Biosphere Research Center,University of the Ryukyus,Okinawa 903-0213,Japan;Japan Agency for Marine-Earth Science and Technology(JAMSTEC),Global Oceanographic Data Center(GODAC),Kanagawa 236-0001,Japan

[1]Kazuhiko Fujita;Yoji Kanda;Takashi Hosono-.Light is an Important Limiting Factor for the Vertical Distribution of the Largest Extant Benthic Foraminifer Cycloclypeus carpenteri)[J].地球科学学刊（英文版）,2022(06):1460-1468

Extant,Foraminifer,Cycloclypeus,carpenteri,foraminifer,endosymbionts,biont,holobionts

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