[POS] Ecology and Enviromment

[POS-40] Long-term changes in the seasonal responses of fish communities to ocean warming revealed by nonlinear time-series analysis

*Takamitsu Ohigashi^1,2, Reiji Masuda³, Masayuki Ushio² (1. Tohoku Univ. (Japan), 2. HKUST (Hong Kong), 3. Kyoto Univ. (Japan))

Keywords:

Empirical Dynamic Modeling,Community Ecology,Fish,Marine Ecosystem,Climate Change

Rising ocean temperatures driven by global warming significantly influence marine biodiversity and food security. Thus, understanding how fish communities respond to these changes is crucial. While previous research has shown that low-latitude species are shifting their ranges poleward and that fish body sizes tend to decline with increasing temperatures, the specific thermal thresholds influencing these trends remain poorly understood. Moreover, the links between fish temperature sensitivities, distributional range, and body size have not been fully explored. To examine these relationships, we analyzed a long-term dataset collected through underwater observational surveys in Maizuru Bay, Kyoto, Japan. Water temperature and fish abundance have been monitored biweekly from 2002 to 2024, which includes 540 time points covering 113 fish species. We employed nonlinear time-series analysis methods: Unified Information-Theoretic Causality (UIC) to identify causal relationships between temperature and species abundance, and Multiview Distance Regularized S-map (MDR S-map) to quantify the strength of temperature effects on abundance. We then explored how temperature effects correlate with species’ latitudinal distribution centers and body sizes. As a result, fish species were categorized into three types: (1) cold-adapted species that are negatively influenced by warming and absent beyond a certain threshold; (2) warm-adapted species that are positively affected by warming but absent below a certain threshold; and (3) generalist species that occur across a broad temperature range. Furthermore, species distributed at higher latitudes tend to exhibit stronger negative responses to rising temperatures. Notably, while such negative correlations between temperature effect and latitudinal distribution center were mostly limited to spring through fall in the earlier period (2002–2013), similar patterns have frequently appeared in winter during the later period (2014–2024). These findings suggest that fish species previously unaffected by winter temperatures are now responding, likely due to progressive warming. Further studies are needed to clarify how these patterns are linked to broader community dynamics and range shifts under ongoing climate change.