Combined Effect Of Interspecies, Feeding And UV-B Stress On Experimental Population Dynamics Of Skeletonema Costatum

Red tide was a global marine ecological calamity too.In recent years,there hasbeen an increase in frequency,affected area and extent of injury of red tide outbreaksin coastal waters of our country.Due to the worsened cultural environment andincreased nutrient enrichment,red tides occurred more frequency and greatharm,nutrient enrichment and harmful red tides in coastal waters had become one ofthe most important fields among worldwide-concerned,newly-emerging significantmarine environmental problems,which were associated with global changes and inbad need of being studied and solved.Zooplankton grazing played an important rolein the development of red tides,marine zooplankton selective grazing cansignificantly affect the phytoplankton community dynamics and control the rhythm,scale and fate of marine primary productivity.Enhanced UV-B (280nm-320nm)radiation resulting from ozone depletion is one of global environmental problems.Notonly marine organisms but also marine ecosystem can be affected by enhanced UV-Bradiation.UV-B radiation can significantly damage marine microalgae.The maintargets are protein,DNA and photosynthetic pigments,and so on.A common red tide-Skeletonema costatum was selected to serve as experimental materials,and its growthwere estimated under controlled laboratory conditions when stressed by othermicroalgae,zooplankton grazing and enhanced UV-B radiation.The results couldsupply experimental base to answer the effect of enhanced UV-B radiation,zooplankton grazing and interspecies on red tides,hence enhance our ability tounderstand and mitigate red t ides.Results showed:1 Effects of different initial cell densities of S.costatum on population growth ofS.costatumThe solitary culture and co-culture methods were used to examine the effects of initial cell densities of S.costatum and different species of microalgae on populationgrowth of S.costatum.The results showed that:The different initial cell densities ofS.costatum have the apparent effects on its population growth.With promotion of theinitial cell density,the time of entering exponential phase and stationary phase couldbe shortened,and the maximum population density could be decreased under solitarycultivated conditions.2.The change of population growth of S.costatum co-culture with three differentkinds of marine microalgaeThe different effects were presented on population growth of S.costatum whenstressed by different microalgae.The inhibitation effect of three species of co-culturedmicroalgae on S.costatum was P.helgolandicavar＞Ⅰ.galbana 8701＞N.closterium;The different initial cell densities of three species of co-cultured microalgae alsoaffected population growth of S.costatum,the inhibitation effect on S.costatum wasincreased gradually with increasing of initial cell densities of three species ofco-cultured microalgae;the inhibitation effects were showed with curtateexponential phase and stationary phase,and decreased the maximum populationdensity of S.costatum.3 Effect of zooplankton grazing on population growth of S.costatum undersolitary cultivatedThe diet-concentration differentia calculational method and experimentalecological method were selected to study the effect of zooplankton grazing onpopulation growth of S.costatum under solitary cultivated with other three speciesmicroalgae.The grazing rate of three species zooplankton from high to low was:B.plicatilis＞S.inopinus＞Harpacticus.The max grazing rate values of B.plicatilis,S.inopinus,Harpacticus were 403 cells ind^-1 h^-1,157cells ind^-1 h^-1,15cells ind^-1 h^-1respectively;Filtering rate were presented in another order,the order of filtering ratefrom high to low was S.inopinus＞B.plicatilis＞Harpacticus,The max filtering ratevalues of S.inopinus,B.plicatilis,Harpacticus were:0.0057 ml ind^-1 h^-1,0.0031 mlind^-1 h^-1,0.0023 ml ind^-1 h^-1;The effect of B.plicatilis grazing on S.costatum wasvaried under different initial cell density of S.costatum under solitary cultivated conditions,the inhibitation effect of B.plicatilis on S.costatum was increasedgradually with increasing of initial cell densities of S.costatum.,4 Effect of zooplankton grazing on population growth of S.costatum underco-cultivated conditionThe diet-concentration differentia calculational method and experimentalecological method were selected to study the effect of zooplankton grazing onpopulation growth of S.costatum under co-cultivated conditions with other threespecies microalgae.Population growth of S.costatum was altered by ingestion ofB.plicatilis under co-cultivated condition with other three species microalgaerespectively,the population cell density of S.costatum was decreased significantly incultured system of P.helgolandicavar,and there were enhanced growth effect ofS.costatum in cultured system of I.galbana 8701 and N.closterium;the inhibitationeffect of B.plicatilis on S.costatum was decreased gradually with increasing of initialcell densities of three species of co-cultured microalgae.5 Effect of enhanced UV-B radiation on population growth of S.costatum undersolitary cultivatedThe ecotoxicological method was used to determine the effect of enhanced UV-Bradiation on population growth of S.costatum under solitary cultivated with otherthree species microalgae.The results were showed as follows:UV-B radiation couldstimulate the growth of S.costatum when the dose was lower than 1.2J/m² while UV-Bradiation also exhibited inhibitation effect to the growth of S.costatum when the dosewas higher than 1.8J/m²,and inhibitation effect was enhanced with the increasing ofUV-B radiation dose;The effect of enhanced UV-B radiation on S.costatum waschanged under different initial cell density of S.costatum under solitary cultivatedconditions,the inhibitation effect of enhanced UV-B radiation on S.costatum waspresented an increasing first and then decreasing gradually with increasing of initialcell densities of S.costatum;6.Effect of enhanced UV-B radiation on population growth of S.costatum underco-cultivated conditionsThe ecotoxicological method was used to determine the effect of enhanced UV-B radiation on population growth of S.costatum under co-cultivated conditions withother three species microalgae.The results were showed as follows:Populationgrowth of S.costatum was changed by enhanced UV-B radiation under co-cultivatedcondition with other three species microalgae respectively,the population cell densityof S.costatum was decreased significantly in cultured system of P.helgolandicavar,and there were enhanced growth effect of S.costatum in culturedsystem of L galbana 8701 and N.closterium;the inhibitation effect of enhanced UV-Bradiation on S.costatum was increased gradually with increasing of initial celldensities of three species of co-cultured microalgae.7 Combined effect of enhanced UV-B radiation and ingestion of B.plicatilis onpopulation growth of S.costatum under solitary cultivated and co-cultivatedconditionsThe experimental ecological method and statistics method were selected todetermine the combined effect of enhanced UV-B radiation and ingestion ofB.plicatilis on population growth of S.costatum under solitary cultivated andco-cultivated conditions with other three species microalgae.The results were showedas follows:Combined effects of lower dose (0.6 J/m²,1.2 J/m²) UV-B radiation andB.plicatilis grazing had decreased inhibitations effect on population growth ofS.costatum,while an enhanced inhibitations effect was presented when joint stressedby higher dose (＞1.8 J/m²) UV-B radiation and B.plicatilis grazing;the inhibitationeffect stressed by Combined effects of UV-B radiation and B.plicatilis grazing onS.costatum was decreased gradually with increasing of initial cell densities ofS.costatum under solitary cultivated conditions;The inhibitation effect stressed bycombined effects of UV-B radiation and B.plicatilis grazing on population growth ofS.costatum can be changed under the co-cultured system of three species microalgae.The inhibitation effect of three species of co-cultured microalgae on populationgrowth of S.costatum was P.helgolandicavar＞L galbana 8701＞N.closterium;Thedifferent initial cell densities of three species of co-cultured microalgae also affectedpopulation growth of S.costatum under combined effects of UV-B radiation andB.plicatilis grazing,the population density of S.costatum was decreased gradually with increasing of initial cell densities of three species of co-cultured microalgae.