Exploring photosymbiotic ecology in planktic foraminifers with chamber-by-chamber isotope analyses

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This study examined chamber-by-chamber stable isotopes (carbon and oxygen) of foraminiferal individuals to identify photosymbiotic signals. We observed an ontogenetic increase in carbon isotopes of up to 2.4 permil, accompanied by relatively stable, negative oxygen isotopes, in the symbiotic species. In contrast, carbon and oxygen isotopes showed significant positive correlation during ontogeny in the asymbiotic species. These two ecological groups produce contrasting isotopic profiles, thereby our ontogenetic isotopic analyses of individual specimens can be used to identify algal photosymbiosis in fossil foraminifers. The chamber-by-chamber isotope analyses with individual ontogeny have great advantages in analyzing rare occurring species because of only one individual is required to describe ontogenetic isotopic history.