Spring protistan communities in response to warming in the northeastern East China Sea

The northeastern East China Sea is a highly dynamic marine ecosystem influenced by seasonally varying water mass properties. However, despite being among the world's fastest-warming ocean, there has been limited investigation into the impacts of warming on protistan communities. We collected seawater from two stations (E42 and E46) with different natural protist communities and environmental attributes to investigate the acclimation of the two communities to artificially elevated temperatures (ambient T, +2, and +4 °C). Nutrient and Chl-a conditions reflected oceanographic differences, providing insights into protistan community dynamics. Notably, small-sized autotrophic protists prevailed in the phosphate-deficient E42 community, with mid-incubation heterotrophic conversions. Higher temperatures exacerbated the effects of the P deficiency on the E42 community. While the proportions of Bacillariophyta increased only in the nutrient-balanced E46 communities, those of mixotrophic dinoflagellates increased with elevated temperature, regardless of P deficiency, suggesting that mixotrophy likely aids adaptation in changing marine environments. In summary, the findings of this microcosm study illuminate the potential modulation of spring protistan communities in the northeastern East China Sea under anticipated future warming.