Studies On Responses Of Phytoplankton And Community Structure To Ocean Acidification

Ocean acidification caused by the rising atmospheric CO₂ concentration has been paid attention worldwide.In this paper,we conducted an indoor acidification simulation experiment for ocean acidification,and the effects of ocean acidification on the growth and nutritional quality of different types of phytoplankton were studied from the perspective of stoichiometry and food chain;We used in-situ mesocosm experiments to study the effects of ocean acidification on the growth of phytoplankton in different seasons and sizes and community structure.And then,the potential effects on the feeding,growth and development of filter-feeding shellfish were discussed.The main research results were as follows:1.Responses of different types of phytoplankton?Platymonas subcordiformis,Chlorella vulgaris,Phaeodactylum tricornutum,Dicrateria sp.,Emiliania huxleyi?to ocean acidification.The results indicated that,?1?The cell density of the five kinds of microalgae were promoted by elevated CO₂ concentration?P<0.05?;for the value of?,E.huxleyi was the highest,31.8%higher than the control group,followed by P.subcordiformis?13.5%?and C.vulgaris?5.9%?.?2?The cellular chlorophyll a contents of C.vulgaris was increased significantly by elevated CO₂ concentration,and P.subcordiformis,E.huxleyi and Dicrateria sp.were significantly reduced,However,there were no significant effect on P.tricornutum.?3?The maximal efficiency of PSII in a dark-adapted state?F_v/F_m?of P.tricornutum elevated remarkably in the beginning of the experiment,photochemical quenching?qP?of E.huxleyi improved,non-photochemical quenching?NPQ?of E.huxleyi and Dicrateria sp.decreased significantly,and the maximum relative electron transport rate?rETRmax?of P.tricornutum and P.subcordiformis,the initial slope of rapid light curves???of Dicrateria sp.increased significantly?P<0.05?.But high CO₂concentration has no remarkable effect on chlorophyll fluorescence parameters of C.vulgaris?P>0.05?.?4?High CO₂ concentration could increase carbon content and/or decrease nitrogen or phosphorus content,and then increase C/N or C/P ratio of phytoplankton.However,there were species different,both of the C/N,C/P ratio for P.subcordiformis,C/P ratio of C.vulgaris and E.huxleyi and C/N ratio of P.tricornutum were significantly increased?P<0.05?,there were no remarkable effect on Dicrateria sp..Therefore,the growth rate of P.subcordiformis,C.vulgaris,E.huxleyi and P.tricornutum accelerated under the high CO₂ concentration,whereas nutrition quality declined.2.Effects of ocean acidification on brown tide algae-Aureococcus anophagefferens and Argopecten irradians feeding on different concentrations of Aureococcus anophagefferens.?1?The cell density and?of Aureococcus anophagefferens were promoted by elevated CO₂ concentration,and the average growth rates was 1.7%higher than the control group;F_v/F_m??actual photochemical efficiency?Y?II??qP?rETR_maxand?the light saturation point?I_k were increased significantly?P<0.05?,promoted growth by rising photosynthesis capacity;The contents of C,N,P and the molar ratios of elements?C/N,C/P?did not change significantly?P>0.05?.?2?The feeding rate?FR?of medium-sized Argopecten irradians to A.anophagefferens rised first and then declined with the increase of algae concentration.when the concentration of A.anophagefferens was 1.5ug/L,the highest FR was 0.7461?g/ind·h,and FR was lower than chlorella at high concentration;absorption efficiency?AE?was very low,with a rang of-1%-1%.Ocean acidification promoted the growth of the population of A.anophagefferens and will greatly increase the likelihood of brown tide outbreaks,at the same time,it inhibited the FR and AE of Argopecten irradians on A.anophagefferens,which will cause serious damage to the survival,growth and development of the filtering shellfish.3.Effects of ocean acidification on phytoplankton with different particle sizes in spring in Sanggou Bay We used the in-situ mesocosm experiment to research the effects of ocean acidification on phytoplankton with different particle sizes in spring in Sanggou Bay,The results showed that:?1?When the nutrient content(PO₄^3--P,DIN,Si O₃^2--Si)was sufficient,ocean acidification had no significant effect on the growth of phytoplankton with different particle size?P>0.05?;when P was limited,the content of chlorophyll a ranged from 2-20?m significantly increased in pH 7.9 and 7.6 group?P<0.05?,which promoted the growth of nanophytoplankton;with P and N restrictions,the number of picophytoplankton increased significantly in pH 7.9 group,phytoplankton particle size structure has been changed.The level of available nutrient content affected the degree of influence of ocean acidification on the growth and particle size structure of phytoplankton in different sizes.?2?The growth of phytoplankton with shellfish was not limited by nutrient content.the dual function of ocean acidification and the feeding activity significantly promoted the growth of picophytoplankton?P<0.05?,the proportion had been increased,and changed the phytoplankton particle size structure.Patinopecten yessoensis had a high food intake for nanophytoplankton but had low intake of picophytoplankton.4.Effects of ocean acidification on the growth and community structure of phytoplankton in autumn in Sanggou Bay Phytoplankton dominant species and environmental conditions vary widely in different seasons.We used the enclosure experiment to research the effects of ocean acidification on the growth and community structure of phytoplankton in autumn in Sanggou Bay,The results turned out that:?1?The nutrient content in the mesocosm is basically sufficient?except the DIN limit in the later period of the experiment?,ocean acidification?pH7.6?had no significant effect on the growth of phytoplankton with different particle sizes?P>0.05?.?2?Ocean acidification reduced the number of diatoms in the algae group and had no significant effect on the total abundance?P>0.05?.the number of dominant species was decreased in the middle of the experiment,and the dominance of Thalassiosira sp.was the highest.ocean acidification promoted the growth of Thalassiosira sp.and Chaetoceros sp.;At the end of the experiment,DIN limited,the number of dominant species was reduced,and the dominance of Nitzschia sp.was highest.ocean acidification promoted the growth of Nitzschia sp.and Thalassiosira sp..Phytoplankton community diversity changed from low diversity?1.5<H?<2.49,0.68<J<0.73?to very low diversity?H?<1.5?.?3?C.gigas' s food intake on micro-and nano-phytoplankton was higher than picophytoplankton.under the condition of ocean acidification,the feeding activities of Crassostrea gigas and zooplankton significantly promoted the growth of micro-and nano-phytoplankton?P<0.05?,and the total biomass increased.The growth rate of micro-and nano-phytoplankton were higher than the feeding rates of zooplankton and shellfish,and the biomass of micro-and nano-phytoplankton were increased in the short term.?4?Ocean acidification reduced the number of phytoplankton species in the shellfish group,and the total abundance of diatoms was increased,which significantly promoted the growth of Thalassiosira sp.and Chaetoceros sp..the number of dominant species remained the same,Thalassiosira sp.as a new dominant species replaced Chaetoceros lorenzianus;the diversity of phytoplankton community remained low diversity.