Study On Ecological Characteristics Of Phytoplankton After Sailing And Unloading Of Ship’s Ballast Water

The ship’s ballast water is used to ensure the safety of the ship’s maritime navigation.During the shipping process,the ship’s draught is adjusted by injecting or discharging ballast water into the hull ballast tank according to the ship’s current loading condition and environmental conditions.Thereby providing stability for the ship,ensuring that the ship can maintains smooth operation.Therefore,marine life will inevitably be transferred between the source port and the destination port through the injection or discharge of ship’s ballast water.The safe navigation of ships requires the ship’s ballast water as an important guarantee.However,the ship’s ballast water also becomes an important way to invade alien species by breaking geographical isolation^[1].In this paper,the phytoplankton simulation experiments of different initial densities and phytoplankton were carried out to explore the dynamic changes and population response characteristics of different phytoplankton in the dark environment,Simulate emissions after dark processing,regain lighting and set different environmental factors.After darkness,the chlorophy∥fluorescence kinetics technique was used to investigate the photosynthetic activity characteristics of different phytoplankton in situ,and the population response of different phytoplankton after re-entering a good environment and the variation characteristics of various photochemical parameters were explored.The ecological characteristics of phytoplankton after ship ballast water navigation and unloading were studied.The main findings are as follows:（1）The Platymonas helgolandica average growth inhibition rate was significantly higher in the first 3 days,and the cell number decreased the most in the first 3 days.After the third day,the average growth inhibition rate is in a state of volatility,and the overall state is a tendency to decrease;in the first seven days of dark treatment,there is a great fluctuation in growth inhibition rate,that is,the number of cells fluctuates greatly.Until the dark day 10,the removal rate of Pl.helgolandica with an average density of 5 cells/ml reached 100%,and the remaining initial density of Pl.helgolandica was still alive for 14 days.The low density（3cells/m L）of Pl.helgolandica recovered after darkness can still reach a higher population density level（1×10³cells/m L）after two weeks of light recovery;For the light recovery density of 3 and 3×10⁴cells/m L dark-treated Pl.helgolandica,the population recovery ability was weaker than that of the un-treated group（P<0.05）.（2）The Skeletonema costatum growth inhibition rate on the first day and the third,fourth,and sixth days of darkness on average was at a higher level.On the sixth day,for each initial density level of S.costatum,there was a great fluctuation in growth inhibition rate,that is,the algal cell density fluctuated greatly.Until the 13th day of darkness,the removal rate of S.costatum with an average density of 5 cells/ml was100%,and the remaining initial density of S.costatum was still alive for 14 days.After light treatment of the dark-treated S.costatum,it was found to still have a population recovery ability.However,at each initial density,the dark-treated S.costatum was lower in density than the untreated S.costatum for 14 days,with an average reduction of about20.54%.（3）Two groups of higher density Prorocentrum micans with initial densities of 5×10²cells/m L and 5×10³cells/m L can still grow and reproduce on the first day in the dark.Overall,the cell growth inhibition rate in the first 3 days was on a gradual increase,and the average cell growth inhibition rate was the highest on the third day.Subsequent growth inhibition rates were in a downward trend overall,but on the sixth day a second peak of death was ushered in.On the 9th day of darkness,the Pr.micans removal rate of the average density of 5 cells/m L reached 100%,and the remaining initial density of Pr.micans dark treatment for 14 days still survived.After the dark treatment of the Pr.micans,the dark treatment significantly inhibited the growth of the P.micans after the restoration of light.The dark-treated algae had a much lower density than the untreated Pr.micans on the 14th day after the light recovery,and the average was only 22.69%of the untreated Pr.micans density.（4）For the Pl.helgolandica and S.costatum with the same average initial density,After different days of darkness（simulated ballast age）,the difference in Fv/Fm between the two algae was extremely significant.The Fv/Fm of S.costatum algae responded more strongly to darkness and was in a process of decreasing,while Pl.helgolandica algae Fv/Fm fluctuated during the dark treatment but decreased slowly;At the same time,there was a significant difference in the ETR values of Pl.helgolandica and S.costatum（P<0.01）.The first two days of the two algae increased their ETR,and then the two lowering processes were similar to Fv/Fm.In the light recovery experiment,the Fv/Fm of Pl.helgolandica in dark 3 days and dark 7 days fluctuated the most under each recovered light intensity,and ETR also showed this characteristic.After light recovery,the chlorophyll content of Pl.helgolandica was significantly increased;Although the initial Fv/Fm was lower in the dark days after dark days（the average on the 9th day of darkness was 0.112）,the Fv/Fm of S.costatum was basically after light recovery under the four light recovery intensities（3-5 days）returning to the maximum and maintaining a certain range,can restore good optical activity.Exploring the changes of populations of different kinds of phytoplankton after navigation and unloading can enhance the understanding of viable organisms in ballast water and obtain more complete species information.Three phytoplankton species in three different categories:Platymonas helgolandica,Skeletonema costatum,and Prorocentrum micans.When the initial density is 5cell/ml and the low density is ballasted（dark）,the survival days are Pr.micans<S.costatum<Pl.helgolandica,and three algae that have experienced darkness and light recovery density of only 3cells/ml.The population recovery ability of the two species is Pr.micans<Pl.helgolandica<S.costatum;after further photosynthetic activity characteristics of Pl.helgolandica and S.costatum,it was found that S.costatum significantly reduced its Fv/Fm,ETR and chlorophyll content in the dark,while these values of Pl.helgolandica are more fluctuating and the degree of reduction is lower than that of S.costatum;in the light recovery experiment,The chlorophyll content of Pl.helgolandica and S.costatum increased significantly and both recovered good light and activity.Therefore,there is a big difference between the survival strategies and photosynthetic activities of different types of phytoplankton in ship ballast water,and whether different types of phytoplankton are below the D-2 uniform standard can guarantee no more invasion.Still worthy of further study.