Compound-specific isotope analysis (CSIA) application to host and symbiont species within a symbiotic partnership, which are corals and their algal symbionts, respectively, allows us to quantify the trophic interaction between two different species within a symbiosis such as the flux of energy and nutrients from algal symbionts to animal hosts. Therefore, we established an isolation method of algal symbionts, zooxanthellae, from corals, which minimizes the contamination of coral tissues and the breakage of algal cells for the CSIA application. Applying a multiple filtration and a weak centrifugation, we successfully purified algal symbionts from coral tissues enough to measure the nitrogen isotope ratios of amino acids of algal symbionts, such that the isotope ratios are 7.4‰ and 4.0‰ for glutamic acid and phenylamine for a soft coral, the zoanthidZoanthussp. The trophic position estimated based on these isotope ratios is 1.0 for the algal symbionts, which is clearly distinguished from that (i.e., trophic position is 2.0) of coral hosts. Thus, the purification method established in our study can be useful for evaluating the trophic interaction between host and algal symbionts for corals.

The di-(anteiso-C₁₅alkyl) glycerol diether (hereafter, theanteiso-C₁₅bacterial diether), putatively identified as a constituent of characteristic ether lipids in some anaerobic bacteria, exhibits considerable potential as a proxy for reconstructing past variations in sedimentary oxygenation and bottom-water ventilation. However, its structural characterization has thus far been limited to mass fragmentation analysis and comparison with the straight-chain C₁₆diether homolog rather than the C₁₅diether. In order to obtain a reference standard and to enable unambiguous structural confirmation and fragmentation analysis, I conducted a relatively straightforward, short-step chemical synthesis of theanteiso-C₁₅bacterial diether. Comparison of the synthesized compound with chromatographic behaviour and mass spectra of its TMS ether derivative reported from sedimentary extracts demonstrated identity with the natural product. In addition, the characteristic mass fragmentation patterns, comparison of chromatographic behaviour, and mass spectra of its TMS ether derivative with synthesized straight-chain C₁₅diether was also conducted.