Estimating photophysiological condition of endosymbiont-bearing Baculogypsina sphaerulata based on the holobiont color represented in CIE L*a*b* color space

Symbiont-bearing large benthic foraminifers (LBFs) are widely distributed around coral reefs. If the physiological responses of LBFs to environmental changes can be recognized at an individual level, LBFs could serve as highly accurate bioindicators. In this study, chlorophyll a, respiration, and photosynthesis of Baculogypsina sphaerulata individuals were measured, and whether these physiological traits could be estimated based on the color of the holobiont (foraminifera and the diatom symbionts) was examined. Chlorophyll a content was estimated using a* and b* values of holobiont color represented in CIE L*a*b* color space. Photosynthetic performance decreased significantly with increasing whiteness (L*). These results indicated chlorophyll content as well as photosynthetic performance of Baculogypsina could be directly estimated using the holobiont color. The increased whiteness in color and decreased photosynthetic performance were mainly observed under low-light environment, possibly indicating symbiotic algae were shrunk into the central part of the host shell due to prolonged exposure to adverse conditions.