Long‐Term Variation in Mesozooplankton Biomass Caused by Top‐Down Effects: A Case Study in the Coastal Sea of Japan

Kodama, Taketoshi; Igeta, Yosuke; Iguchi, Naoki

doi:10.1029/2022gl099037

Cited by 7 publications

(3 citation statements)

References 67 publications

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“…Subarctic waters, such as the Oyashio region and the northern areas of the Sea of Japan, are important feeding grounds during summer and fall, when large zooplankton, such as Euphausia pacifica and Neocalanus spp., are available, in addition to the East China Sea and Yellow Sea, where Calanus sinicus is available (Yatsu, 2019). The reduced chlorophyll‐a concentrations following the 1976/1977 climatic regime shift and the flourishing of Japanese sardine have been suggested to have caused a decrease in summer mesozooplankton biomass in the 1980s in the Oyashio waters (Ito et al., 2007; Tadokoro et al., 2005) and the Sea of Japan (Kodama et al., 2022). Apart from the direct competition for food, Fuji et al.…”

Section: Discussionmentioning

confidence: 99%

Fish weight reduction in response to intra‐ and interspecies competition under climate change

Lin,

Ito

2024

Fish and Fisheries

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Section: Discussionmentioning

confidence: 99%

Fish weight reduction in response to intra‐ and interspecies competition under climate change

Lin,

Ito

2024

Fish and Fisheries

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“…and anchovies (Engraulis spp.) play a key role in the transfer of energy from plankton to higher trophic levels in pelagic ecosystems (Curry et al, 2000;2011;Kodama et al, 2022a). They inhabit the eastern and western boundaries of subtropical oceans worldwide, including the productive coastal upwelling regions and the western North Pacific, and often dominate zooplankton feeders with their enormous biomass (Checkley et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Geographic, seasonal and ontogenetic variations of δ15N and δ13C of Japanese sardine explained by baseline variations and diverse fish movements

Sakamoto¹,

Kodama²,

Horii³

et al. 2023

Preprint

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Understanding and predicting variability in the stable isotope ratios of nitrogen and carbon (δ15N and δ13C, respectively) of small pelagic fish is crucial to enable isotopic studies of a variety of marine predators that feed on them. However, because the isotope ratios reflect plastic feeding habits and fish migration in addition to baseline variation, their predictions require a mechanistic understanding of how each factor contributes. Here, we investigated the habitat-wide variability of δ15N and δ13C of the Japanese sardine Sardinops melanostictus in the western North Pacific and its marginal seas (the East China Sea and the Sea of Japan). By combining this with the archived particulate organic matter (POM) dataset as a baseline, we aimed to understand how ecological processes and baseline fluctuations affect isotope ratios of the sardine. Both δ15N and δ13C of sardine showed significant geographical and seasonal trends, with higher values in southern nearshore areas, including the Seto Inland Sea, intermediate values in marginal seas and lower values in Pacific offshore areas. As the variations were largely consistent with the geographic and temporally integrated seasonal trends of isotope ratios of POM, respectively, the baseline variations are the main determinant of sardine isotope composition. The trophic levels of sardine are therefore not significantly different between regions, with possible minor increases in the southern nearshore area. Adults showed less geographic variation than larvae and juveniles, likely due to slower turnover periods and wider migration ranges. Although larval and juvenile isotope ratios in marginal seas mostly reflected the local baseline, those in the Pacific offshore often reflected the baseline in the neighbouring southern region, suggesting contrasting juvenile movements between regions. Our results suggest that the δ15N and δ13C of Japanese sardine strongly reflect baseline variations, but can also be influenced by life-stage- and region-dependent fish movements, thereby demonstrating both the possibility and difficulty of mechanistically modelling the isoscapes of lower trophic level species.

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“…The δ 15 N in animal tissues varies with trophic position. In the SOJ, the zooplankton biomass has been found to be negatively coupled with the biomass of small pelagic fish over the last half-century, and, hence, food-web structure may periodically change (Kodama et al, 2022a). Thus, the baseline δ 15 N in marine ecosystems is vital for identifying changes in nitrogen dynamics in the SOJ.…”

Section: Introductionmentioning

confidence: 99%

Multiple nitrogen sources for primary production inferred fromδ¹³C andδ¹⁵N in the southern Sea of Japan

Kodama,

Nishimoto,

Nakamura

et al. 2023

Biogeosciences

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Abstract. Carbon and nitrogen dynamics in the Sea of Japan (SOJ) are rapidly changing. In this study, we investigated the carbon and nitrogen isotope ratios of particulate organic matter (δ13CPOM and δ15NPOM, respectively) at depths of ≤100 m in the southern part of the SOJ from 2016 to 2021. δ13CPOM and δ15NPOM exhibited multimodal distributions and were classified as belonging to four classes (I–IV) according to the Gaussian mixed model. A majority of the samples were classified as class II (n=441), with a mean ± standard deviation of δ13CPOM and δ15NPOM of -23.7±1.2 ‰ and 3.1 ± 1.2 ‰, respectively. Compared to class II, class I had significantly low δ15NPOM (-2.1±0.8 ‰, n=11), class III had low δ13CPOM (-27.1±1.0 ‰, n=21), and class IV had high δ13CPOM (-20.7±0.8 ‰, n=34). All the class I samples, whose δ15NPOM showed an outlier of total datasets, were collected in winter and had a comparable temperature and salinity originating in Japanese local rivers. The generalized linear model demonstrated that the temperature and chlorophyll-a concentration had positive effects on δ13CPOM, supporting the idea that the active photosynthesis and phytoplankton growth increased δ13CPOM. However, the fluctuation in δ15NPOM was attributed to the temperature and salinity rather than nitrate concentration, which suggested that the δ15N of source nitrogen for primary production is different among the water masses. These findings suggest that multiple nitrogen sources, including nitrates from the East China Sea, Kuroshio, and Japanese local rivers, contribute to the primary production in the SOJ.

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Long‐Term Variation in Mesozooplankton Biomass Caused by Top‐Down Effects: A Case Study in the Coastal Sea of Japan

Cited by 7 publications

References 67 publications

Fish weight reduction in response to intra‐ and interspecies competition under climate change

Fish weight reduction in response to intra‐ and interspecies competition under climate change

Geographic, seasonal and ontogenetic variations of δ15N and δ13C of Japanese sardine explained by baseline variations and diverse fish movements

Multiple nitrogen sources for primary production inferred fromδ¹³C andδ¹⁵N in the southern Sea of Japan

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Long‐Term Variation in Mesozooplankton Biomass Caused by Top‐Down Effects: A Case Study in the Coastal Sea of Japan

Cited by 7 publications

References 67 publications

Fish weight reduction in response to intra‐ and interspecies competition under climate change

Fish weight reduction in response to intra‐ and interspecies competition under climate change

Geographic, seasonal and ontogenetic variations of δ15N and δ13C of Japanese sardine explained by baseline variations and diverse fish movements

Multiple nitrogen sources for primary production inferred fromδ13C andδ15N in the southern Sea of Japan

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Multiple nitrogen sources for primary production inferred fromδ¹³C andδ¹⁵N in the southern Sea of Japan