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Open AccessArticle
Seasonal and Interannual Variations (2019–2023) in the Zooplankton Community and Its Size Composition in Funka Bay, Southwestern Hokkaido
by
Haochen Zhang
Haochen Zhang 1,
Atsushi Ooki
Atsushi Ooki 1,2
,
Tetsuya Takatsu
Tetsuya Takatsu 1
and
Atsushi Yamaguchi
Atsushi Yamaguchi 1,2,*
1
Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan
2
Arctic Research Center, Hokkaido University, Kita-21 Nishi-11 Kita-ku, Sapporo 001-0021, Japan
*
Author to whom correspondence should be addressed.
Oceans 2025, 6(3), 49; https://doi.org/10.3390/oceans6030049 (registering DOI)
Submission received: 30 May 2025
/
Revised: 13 July 2025
/
Accepted: 23 July 2025
/
Published: 4 August 2025
Abstract
Funka Bay, located in southwest Hokkaido, is a vital fishing area with a shallow depth of less than 100 m. Seasonal flows of the Oyashio and Tsugaru Warm Current affect the marine environment, leading to significant changes in zooplankton communities, yet limited information is available on these variations. This study used ZooScan imaging to analyze seasonal and interannual changes in zooplankton abundance, biovolume, community structure, and size composition from 2019 to 2023. Water temperature was low in March–April and high in September–November, with chlorophyll a peaks occurring from February to April. Notable taxa such as Thaliacea, Noctiluca, and cladocerans were more common in the latter half of the year. Interannual variations included a decline in large cold-water copepods, Eucalanus bungii and Neocalanus spp., which were abundant in 2019 but decreased by 2023. Zooplankton abundance and biovolume showed synchronized seasonal changes, correlating with shifts in the Normalized Biovolume Size Spectra (NBSS) index, which measures size composition. Cluster analysis identified eight zooplankton communities, with Community A dominant from July to December across all years, while Community D was prevalent in early 2019 but was replaced in subsequent years. Community E emerged from March to April in 2021–2023. In 2019, large cold-water copepods were dominant, but from 2020 to 2023, appendicularians became the dominant group during the March–April period. The decline in large copepods is likely linked to marine heat waves, influencing yearly zooplankton community changes.
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MDPI and ACS Style
Zhang, H.; Ooki, A.; Takatsu, T.; Yamaguchi, A.
Seasonal and Interannual Variations (2019–2023) in the Zooplankton Community and Its Size Composition in Funka Bay, Southwestern Hokkaido. Oceans 2025, 6, 49.
https://doi.org/10.3390/oceans6030049
AMA Style
Zhang H, Ooki A, Takatsu T, Yamaguchi A.
Seasonal and Interannual Variations (2019–2023) in the Zooplankton Community and Its Size Composition in Funka Bay, Southwestern Hokkaido. Oceans. 2025; 6(3):49.
https://doi.org/10.3390/oceans6030049
Chicago/Turabian Style
Zhang, Haochen, Atsushi Ooki, Tetsuya Takatsu, and Atsushi Yamaguchi.
2025. "Seasonal and Interannual Variations (2019–2023) in the Zooplankton Community and Its Size Composition in Funka Bay, Southwestern Hokkaido" Oceans 6, no. 3: 49.
https://doi.org/10.3390/oceans6030049
APA Style
Zhang, H., Ooki, A., Takatsu, T., & Yamaguchi, A.
(2025). Seasonal and Interannual Variations (2019–2023) in the Zooplankton Community and Its Size Composition in Funka Bay, Southwestern Hokkaido. Oceans, 6(3), 49.
https://doi.org/10.3390/oceans6030049
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