Yu Saitoh

Incremental analysis of vertebral centra can reconstruct the stable isotope chronology of teleost fishes

1.Isotope analysis has high potential for understanding fish ecology and food-web structure in aquatic ecosystems. The utility of isotope analysis will be greatly improved if we can reconstruct the chronology of several isotopes at multiple growth stages of individual fish. However, no practical methods exist for reconstructing the chronology of light-element isotopes (e.g. δ13C, δ15N, δ34S, and Δ14C) in teleost fishes. Here, we present and test a new analytical approach for reconstructing the isotopic ratios of light isotopes at multiple life-stages in teleost fishes. 2.We sampled an anadromous salmon species, masu salmon Oncorhynchus masou (n = 3), along with water from its natal stream and from the ocean. We subdivided the vertebral centra of the salmon equally into 10 sections and extracted bone collagen from each sample. We then measured the stable sulfur isotope ratios of each vertebral section and compared them with δ34S values of the river water and sea water. We also measured the 87Sr/86Sr ratios of otoliths as a reference indicator of salmon migration between fresh water and the ocean. 3.In all samples, the bone section closest to the centre of the centrum had the lowest δ34S values, which were similar to those of fresh water. The δ34S values gradually increased from the centre to marginal sections, finally reaching constant values similar to those of seawater. The 87Sr/86Sr ratios of sagittal otolith sections had significant inter-individual differences and were consistent with the patterns of variation of the δ34S values of the vertebral sections. 4.Our results show that the vertebral centra of teleost fishes record isotopic information from juvenile to adult life-stages. We suggest that our method can provide reproducible isotopic chronology, even in teleost fishes smaller than 50 cm. This method can be used in isoscape studies and in studies of the ecology of marine teleost fishes. This article is protected by copyright. All rights reserved.

The Effects of Differences in Vegetation on Calcium Dynamics in Headwater Streams

Although organisms can alter dynamics of elements in ecosystems via physiological results, the effects of tree species on ecosystem nutrient dynamics are highly uncertain. A four-fold variation in the calcium concentrations of streams, soils and leaf litters were caused by the planting of Cryptomeria japonica in south-central Japan. In this study, we examined how the calcium dynamics were affected by the planting of C. japonica through strontium isotope analysis. We predicted the planting of C. japonica would result in the calcium concentration increasing because of the significant dissolution of calcium from bedrock. In a forest ecosystem, calcium is usually derived from precipitation and bedrock weathering, and their relative contributions can be estimated using a strontium isotope mixing model. Therefore, we collected stream water, litter, soil, precipitation and bedrock samples from 17 sites in catchments dominated by C. japonica plantation or evergreen broad-leaved forest; after collection, we analyzed the sample chemical compositions and strontium isotope ratios. The calcium concentrations in the stream water and the water-soluble calcium in the soil were significantly higher at sites dominated by C. japonica than at broad-leaved forest sites. Strontium isotope analysis indicated that there was more calcium from the bedrock present in stream water at sites dominated by C. japonica than in stream water at broad-leaved forest sites. Our results showed that watershed-scale dynamics of calcium and other cations can be altered by the type of vegetation in a catchment due to the effects of vegetation on the supply of calcium from bedrock.