Carbon dynamics in photosymbiotic system of planktonic foraminifera

Abstract

Photosymbiosis (endosymbiosis with algae) is widely observed in marine organisms and is considered to be an adaptive strategy to live in oligotrophic oceans. Many species of planktonic foraminifera, which are microfossil organisms, are also known to be photosymbiotic. From the viewpoint of improving the accuracy of paleoenvironmental proxies based on planktonic foraminiferal tests, there is much interest in how the photosynthesis of symbiotic algae affects the geochemical composition of their tests. However, the dynamics of carbon directly related to photosynthesis are still not well known due to the limited number of experimental studies. In this study, we conducted culture experiments on planktonic foraminifera and photosynthesis measurements on them in order to clarify the carbon dynamics of photosymbiotic systems. By measuring and comparing photosynthesis using two different techniques (14C tracer method and fast repetition rate fluorometry method) in two different foraminifera-algal symbiotic systems, it became clear that the origin of the carbon used for photosynthesis was different between the two species. The results suggest that the degree of influence on the chemical composition of the shell may differ between the two species.