Microalgal Inoculation Modulates the Size-Dependent Assembly and Short-Term Stability of Eukaryotic Plankton Communities in Shrimp-Rearing Water

Microalgae-based regulation is increasingly recognized as an eco-friendly strategy for improving water quality and nutrient management in intensive aquaculture systems. Although its effects on bacterial communities have been extensively investigated, its ecological impacts on higher trophic levels—particularly eukaryotic plankton communities across different size fractions—remain poorly understood. In this study, two indigenous microalgae species, Nannochloropsis oculata and Thalassiosira weissflogii, were inoculated into shrimp rearing water to elucidate the dynamics and interactions among microalgae, nutrient factors, and eukaryotic plankton communities across the small-sized (0.22–3 μm) and large-sized (>3 μm) fractions. The results revealed significant differences in the composition and diversity of both plankton size fractions under different microalgae treatments. Partial least squares path modeling indicated that microalgae influenced plankton communities both directly and indirectly through nutrient-mediated pathways. According to the neutral community model, microalgae inoculation was associated with an increased contribution of deterministic processes to community assembly. Variance partitioning further revealed that the large-sized community was primarily governed by microalgae, whereas the small-sized community was mainly shaped by rearing time, indicating size-dependent assembly mechanisms. The average variation degree and coefficient of variation, combined with effect-size analyses, indicated that N. oculata inoculation was associated with higher short-term community stability, an effect most pronounced in the large-sized fraction. Overall, these findings demonstrate that microalgal inoculation modulates the structure, assembly processes, and short-term stability of eukaryotic plankton communities, providing new insights into size-dependent, microalgae-driven assembly mechanisms and their potential to stabilize plankton communities for sustainable aquaculture management.