Studies On The Interaction Of Jellyifsh Blooms And Phytoplankton Community

The interaction of jellyfish blooms and phytoplankton community was studiedvia laboratory controlled experiments and in situ experiments.First, we studied the top-down regulation of phytoplankton by jellyfish viafeeding rate definition. The effects of different microalgal species and cell densitieson the feedings of polyps, ephyrae and medusae of Aurelia sp.1under controlledlaboratory conditions were investigated. Two species of microalgae, Skeletonemacostatum and Prorocentrum donghaiense, were used. With the increasing ofmicroalgal cell desities, the ingestion rates (IR) of polyps and ephyrae increased whilethe clearance rates (CR) decreased, and the IR of ephyrae were higher than those ofpolyps. The adaption of microalgae made IR of polyps increased about ten times.Second, we evaluated the effects of different microalgal species on the growth ofnewly released Aurelia sp.1ephyrae under the controlled laboratory conditions.Results showed that newly released ephyrae can utilize some species of microalgaefor growth in the earliest development stage. Chain diatom Skeletonema costatum anddinoflagellate Prorocentrum donghaiense could not be utilized by ephyrae, while Noctiluca scintillans and chlorophyta Platymonas subcordiformis could support thegrowth for the ephyrae for the first12days. However, the ephyrae fed withphytoplankton could not develop to medusae.Last, we studied the bottom-up regulation of phytoplankton by jellyfish duringrespiration and decomposition. Results suggested that the seawater acidification andhypoxia occurred during the respiration of Nemopilema nomurai in24hours.Meanwhile, inorganic nutrients regenerated by N. nomurai greatly increased theconcentrations of DIN and DIP in the seawater, which led to the increase ofchlorophyll a concentration.The decomposition of N. nomurai led the seawater to significant oxygen deficitand acidification, and it got more severe when the biomass of N. nomurai was higher.Numerous inorganic nutrients were released to the seawater and the structure ofinorganic nutrients was greatly changed and dinoflagellates and chlorophyta bloomed.Furthermore, the abundance of ciliates increased due to the sufficient food.