Succession of phytoplankton community during intensive shrimp (Litopenaeus vannamei) cultivation and its effects on cultivation systems
Abstract As the basic biological element in shrimp cultivation systems, phytoplankton performs irreplaceable ecological functions in aquaculture ecosystem, but knowledge of the its community succession is currently not sufficient. To fill this gap, we performed longitudinal dense sampling in six intensive shrimp (Litopenaeus vannamei) aquaculture ponds to track the time series shift of phytoplankton community at the community and species levels and to discuss the effects of its succession on rearing environment and shrimp. We detected a distinct successional pattern in the phytoplankton community by principal coordinates analysis and time lag regression analysis, and this pattern could be divided into 3 clusters. Canonical correspondence analysis indicated that water temperature, dissolved oxygen, salinity, pH and bacterioplankton (Actinobacteria, Gammaproteobacteria, Verrucomicrobiae, and Acidimicrobiia) were the extrinsic factors that were correlated with the phytoplankton community variation. The a diversity and taxonomic composition of communities in different clusters were discrepant. By random forest regression, we identified biomarkers of phytoplankton succession which was corelated with shrimp cultivation time. Spearman's rank correlation showed that at least one environmental variable was correlated with the biomarkers, which emphasized the interaction between phytoplankton and rearing environment. Moreover, network analysis revealed that correlations among individual phytoplankton and biotic and abiotic factors at different clusters were also discrepant. The decline in biomarkers indicated a bloom of pathogenic Gammaproteobacteria at the end of cultivation, which contribute to disease outbreaks. Overall, our findings imply that the succession of the phytoplankton community during shrimp cultivation follows a process in which phytoplankton succeed from initial establishment driven by abiotic and biotic factors, and this process might affect the function of the aquaculture ecosystem and the health of reared shrimp to some extent.