12:00 PM - 12:15 PM
[HTT16-12] Established an identifying habitat proxy by the combined analysis of δ18O and trace elements for statolith of Todarodes pacificus (Japanese flying squid)
Keywords:biogenic calcium carbonate, oxygen isotope, trace elements, identifying proxy for the migration area, Japanese flying squid
Seawater temperature rises as global warming becomes more serious, and concurrent environmental change forces marine organisms to change their survival strategies. For protecting future marine resources, the ecological response of marine species (e.g., habitat, prey, and migration) to environmental change is the most important information. A Japanese flying squid “Todarodes pacificus” is an important animal in the marine food web, and sensitive to changes in seawater temperatures. Based on recent fishery surveys, Japanese flying squids around the Japanese archipelago are inferred to change their migration patterns, but the details remain unclear.
Geochemical tracers of biogenic calcium carbonate, such as statolith and otolith, are expected to provide insights into marine organisms' migration ecology (e.g., Muto et al. 2022). Although δ18O values, which reflect seawater temperature, can be used to estimate north-south migration history (e.g., Sakamoto et al. 2024), the extensive longitudinal distribution of isothermal zones poses a challenge for estimating habitat areas in the east-west direction. In contrast, the concentrations of some trace elements show an east-west gradient (e.g., Sugiyama et al., 1984) and may serve as indicators for distinguishing between the Japan Sea and the Pacific Ocean. Therefore, a combined analysis of δ18O values and trace element concentrations with a comparable high resolution is expected to provide a reliable reconstruction of the migration history of Japanese flying squid.
A pair of statoliths from Japanese flying squid were analyzed to identify the geochemical tracer that distinguishes between the migration area of the Pacific Ocean and the Japan Sea. The analyzed samples are from six sites: Odawara, Minami-Boso, and Muroto areas in the Pacific Ocean, and Okushiri, Toyama, and Ishikawa areas in the Japan Sea. Highly sensitive δ18O analysis were conducted using a customized stable isotope ratio mass spectrometer (MICAL3c + IsoPrime), and trace-element data were obtained by using LA-ICPMS (Raijin α + Agilent 8900).
The Odawara and Minami-Boso samples on the Pacific Ocean show a flat trend with little variation in δ18O from the core to the edge (SD ~ 0.3‰), while the Muroto sample mainly shows a large increase in δ18O value from ~−1‰ to ~+1‰ and then a decrease to ~0‰ towards the edge. On the Japan Sea, similar to the Pacific Ocean, the Ishikawa samples show a flat trend in δ18O value (SD ~0.5‰), and δ18O values of Okushiri samples show an increase from ~−1‰ to ~+1.5‰, followed by a decrease to 0‰. Moreover, the δ18O values of Toyama samples show a monotonic increase trend from ~−1.5‰ to ~+1‰. δ18O values show multiple patterns regardless of the migration area, indicating that there is no characteristic migration patterns exist in both the Pacific Ocean and the Japan Sea.
Some trace element contents ( e.g., Mg and Mn ) show the same decreasing trend from the core to the edge, irrespective of the migration area. It suggests that these elements reflect changes in the physiological state. Although Sr and Ba contents do not show a specific pattern for each area, Ba contents near the edge of the statolith from the Japan Sea are higher than those from the Pacific Ocean. This is consistent with the differences in Ba content in seawater between the two areas reported in the previous study. However, Ba incorporation of statolith may reflect seawater temperature and physiological effects. Thus, to cancel these effects, it was performed that a comparison with δ18O value as a temperature proxy and a combined analysis of the trace element ratio to Sr, which has a similar chemical behavior as Ba during biomineralization. Our results suggested that Ba/Sr in statolith between the Japan Sea and the Pacific Ocean are statistically different. Furthermore, the linear and quadratic discriminant analysis using Ba/Sr and δ18O can generally discriminate between the Japan Sea and the Pacific Ocean, and the accuracy was over 80% in both cases. We have successfully established an identifying proxy for the migration area of Japanese flying squid by the combined analysis of δ18O (north-south migration areas) and trace elements (east-west migration areas). It is expected to become more robust when applied to adult samples at various sites. This method can potentially be applied to other fish species, regardless of fish and cephalopods.
Geochemical tracers of biogenic calcium carbonate, such as statolith and otolith, are expected to provide insights into marine organisms' migration ecology (e.g., Muto et al. 2022). Although δ18O values, which reflect seawater temperature, can be used to estimate north-south migration history (e.g., Sakamoto et al. 2024), the extensive longitudinal distribution of isothermal zones poses a challenge for estimating habitat areas in the east-west direction. In contrast, the concentrations of some trace elements show an east-west gradient (e.g., Sugiyama et al., 1984) and may serve as indicators for distinguishing between the Japan Sea and the Pacific Ocean. Therefore, a combined analysis of δ18O values and trace element concentrations with a comparable high resolution is expected to provide a reliable reconstruction of the migration history of Japanese flying squid.
A pair of statoliths from Japanese flying squid were analyzed to identify the geochemical tracer that distinguishes between the migration area of the Pacific Ocean and the Japan Sea. The analyzed samples are from six sites: Odawara, Minami-Boso, and Muroto areas in the Pacific Ocean, and Okushiri, Toyama, and Ishikawa areas in the Japan Sea. Highly sensitive δ18O analysis were conducted using a customized stable isotope ratio mass spectrometer (MICAL3c + IsoPrime), and trace-element data were obtained by using LA-ICPMS (Raijin α + Agilent 8900).
The Odawara and Minami-Boso samples on the Pacific Ocean show a flat trend with little variation in δ18O from the core to the edge (SD ~ 0.3‰), while the Muroto sample mainly shows a large increase in δ18O value from ~−1‰ to ~+1‰ and then a decrease to ~0‰ towards the edge. On the Japan Sea, similar to the Pacific Ocean, the Ishikawa samples show a flat trend in δ18O value (SD ~0.5‰), and δ18O values of Okushiri samples show an increase from ~−1‰ to ~+1.5‰, followed by a decrease to 0‰. Moreover, the δ18O values of Toyama samples show a monotonic increase trend from ~−1.5‰ to ~+1‰. δ18O values show multiple patterns regardless of the migration area, indicating that there is no characteristic migration patterns exist in both the Pacific Ocean and the Japan Sea.
Some trace element contents ( e.g., Mg and Mn ) show the same decreasing trend from the core to the edge, irrespective of the migration area. It suggests that these elements reflect changes in the physiological state. Although Sr and Ba contents do not show a specific pattern for each area, Ba contents near the edge of the statolith from the Japan Sea are higher than those from the Pacific Ocean. This is consistent with the differences in Ba content in seawater between the two areas reported in the previous study. However, Ba incorporation of statolith may reflect seawater temperature and physiological effects. Thus, to cancel these effects, it was performed that a comparison with δ18O value as a temperature proxy and a combined analysis of the trace element ratio to Sr, which has a similar chemical behavior as Ba during biomineralization. Our results suggested that Ba/Sr in statolith between the Japan Sea and the Pacific Ocean are statistically different. Furthermore, the linear and quadratic discriminant analysis using Ba/Sr and δ18O can generally discriminate between the Japan Sea and the Pacific Ocean, and the accuracy was over 80% in both cases. We have successfully established an identifying proxy for the migration area of Japanese flying squid by the combined analysis of δ18O (north-south migration areas) and trace elements (east-west migration areas). It is expected to become more robust when applied to adult samples at various sites. This method can potentially be applied to other fish species, regardless of fish and cephalopods.