Patterns of phytoplankton community structure and diversity in aquaculture ponds, Henan, China

Abstract In aquaculture, phytoplankton contribute to primary productivity, helping maintain fishery harvests and water stabilization. To better understand the drivers controlling phytoplankton communities, sampling was conducted during two seasons in 185 aquaculture ponds that cultured five species of aquatic animals (channel catfish, common carp, grass carp, crayfish and largemouth bass). Principal coordinate analysis (PCoA), redundancy analysis (RDA), and generalized linear model (GLM) were applied to quantify the relative importance of multiple factors to phytoplankton species composition and diversity. The PCoA results demonstrated that in spring, phytoplankton species composition showed no distinct differences among the 5 cultivated-animal ponds. In summer, phytoplankton species composition had a distinct pattern, which was clustered into three distinct groups. The RDA results revealed that the variation in the phytoplankton composition was closely correlated with the water temperature, conductivity, dissolved organic carbon (DOC), alkalinity, and nitrate in spring. In summer, different variables, including cultivated animals, alkalinity, pH and dissolved oxygen (DO), were responsible for explaining species composition patterns. In spring, no significant difference in phytoplankton α-diversity was found among the 5 cultivated-animal ponds. In summer, significantly higher α-diversity was found in the channel catfish and crayfish ponds than in the other ponds. GLM analysis showed that phytoplankton density, cultivated animals, and conductivity can be used to explain phytoplankton diversity. Although no effect of cultivated animals was found during the early aquaculture stage, the results from the summer samples demonstrated that cultivated animals have an important influence on phytoplankton communities. Therefore, we suggest that in intensive fish-stocking ecosystems, top-down effect is an important strength on phytoplankton communities. In terms of preventing algal blooms, a low density of phytoplankton is important for maintaining high phytoplankton diversity and water stabilization in aquaculture. Our results can provide useful information for water management practices in aquaculture ponds.