Insights into ecological effects of fish and shellfish mariculture on microeukaryotic community.

To better understand the ecological effects of mariculture, the diversity distribution, determinant and interaction of microeukaryote communities from fish cage and suspended shellfish farming were investigated in three bays of South China Coast. Our alpha and beta diversity analyses showed that the difference of the microeukaryote community between fish and shellfish farming was more significant at local than regional scale, and microeukaryotes respond more to spatial effect than mariculture effect at regional scale. Mantel test, variation partitioning analysis and co-occurrence network analysis revealed that the environmental factors especially chemical and biotic factors contributed more to community assembly in fish than shellfish farming. Based on the comparisons of community composition and determinant between fish and shellfish farming, the effect mechanisms of the two farming types on microeukaryote community were proposed. Fish farming brings significant environmental variation and thus has strong bottom-up impacts on microeukaryotes, while shellfish farming exerts a grazing pressure on microeukaryotes by filter-feeding and has top-down control to them. Furthermore, the network stability analyses revealed weaker community stability in fish than shellfish farming, suggesting that the microeukaryote community was more sensitive to environmental change deduced by fish than shellfish farming. Overall, this study revealed the different influencing mechanisms of fish and shellfish mariculture on microeukaryotes, which will improve the understanding of the ecological effects of mariculture and provide guidance for the management of mariculture under future environmental pressures.