Ionic adjustments do not alter plankton composition in low salinity Penaeus vannamei intensive nursery with synbiotic system

Abstract

ABSTRACT The aim of this study was to test the effect of different ionic adjustments in low salinity water on the composition and temporal variation of plankton from intensive shrimp nurseries with a synbiotic system. For this, a Penaeus vannamei nursery (35 days) was carried out with three treatments: T1 – diluted seawater (control; salinity ∼2.5 g L−1), T2 – salinity ∼2.5 g L−1 with K+ adjustment to approximate the seawater equivalent concentration, and T3 – salinity ∼2.5 g L−1 with Ca:Mg:K ratio adjusted to 1:3:1. Rice bran processed by probiotic microorganisms was used as an organic carbon source. Phytoplankton and zooplankton were sampled weekly and analysed using standard methods. The temporal variation of phytoplankton and zooplankton composition were more pronounced than differences among treatments indicating that the ionic adjustment had little effect on these communities. During the experimental time, the dominant phyla in phytoplankton were Ochrophyta, Cyanophyta and Chlorophyta, whereas zooplankton’s dominant phyla were Ciliophora, Amoebozoa, and Cercozoa. Cyanophyta’s relative abundance was lower than traditional biofloc systems, suggesting a higher control of these microorganisms in synbiotic systems. Ionic adjustments have then a low potential to affect plankton, likely because limitation by these ions was not achieved under the ionic manipulations tested.