[M-IS11] Biogeochemistry

[MIS11-P01] Comparison of isotopic enrichment among taxonomic group of freshwater parasites using stable isotope microanalysis

*Kei Kinoshita¹, Yuji Onishi¹, Keitaro Fukushima¹, Akiko Goto¹, Misako Urabe², Keisuke Koba¹ (1.Department of biology, Graduate School of Science, Kyoto University, 2.Department of enviroment, Shiga Prefecture University)

Keywords:isotope discrimination, parasites

Carbon and nitrogen stable isotope analysis have been used as a method for clarifying the predator-prey relationship in ecosystems. It is known that predators are more concentrated in carbon and nitrogen stable isotope ratios than prey. On the other hand, it has been known that isotopic enrichment is negative in parasites found in aquatic ecosystem, unlike the predator-prey relationship, but the exact cause has not been clarified so far. Therefore, in this study, we thought two factor about specific isotope enrichment of parasites: (1) the possibility that the host tissue which the parasite uses as food cannot be accurately evaluated in previous research, and (2) the possibility that the parasite has different isotope enrichment factor for each strain group.
From 2019 to 2020, parasites were collected from 15 species of fish and 1 species of crustacean around Lake Biwa, and the host sites using the parasites was identified. We used the stable isotope microanalysis method for parasites and used the stable isotope analysis method for the host site. In the result, (1) isotope enrichment compared host site using parasites as food, for example host tissue or contents of digestive tract, are better than compared muscle site used in previous studies. Regarding (2), We revealed that among the 12 parasites of the 6th order that could be analyzed, trematodes and cestodas show positive enrichment as many as predator-prey relationship, unlike previous studies.On the other hand, nematodes, acanthocephalans, copepods, and isopods also showed specific isotopic enrichment. Especially, isotope enrichment in nematodes was observed according to host utilization corresponding to the life stage. It was considered to show isotope enrichment corresponding to host utilization. In addition, we observed that acanthocephalans, copepods, and isopods have unique metabolic pathways corresponding to their strain groups.