Effects Of Temperature On Growth Of Phytoplankton In The Changjiang Estuary And Adjacent Coastal Waters

Field research indicates that since1980s, Harmful algal blooms (HAB) becomemore and more serious in the Changjiang Estuary and Adjacent Coastal Waters,meanwhile the dominant species of HAB evolve from single diatom to diatom anddinoflagellate alternately. Resent studies reveal that not only increased input ofland-based sources nutrients due to human activities, but also changes of climaticconditions lead to the aggravation of HAB, and temperature exerts non-negligible impacton the occurrence of HAB. However, the quantitative description of temperature effect ofbloom algae in the Changjiang Estuary and Adjacent Coastal Waters is limited currently,specially the quantitative relationship that between interannual change of phytoplanktonbiomass and the control mechanism of temperature effect of bloom algae is not clear.Besides, previous studies that focused on temperature effect of bloom algae in theChangjiang Estuary and Adjacent Coastal Waters are all based on laboratory experimentswhere experimental conditions distinguish from the actual conditions, and the resultsmay differ from the actual situation.Thus, in present study, we deployed statistical analysis of on site survey data,Ship-based mesocosm/bottle culture field experiments and numerical simulation tosystemically study①the interannual change temperature effect of phytoplanktonbiomass in the Changjiang Estuary and Adjacent Coastal Waters;②the temperatureeffect control mechanism of typical bloom algae; and their relationship, and③synchronously, evaluate the differences between the field culture experiment and thelaboratory culture experiment. The key results are listed bellow:1. The effect of interannual temperature change on phytoplankton biomass in theChangjiang Estuary and Adjacent Coastal Waters(1) The interannual change pattern of phytoplankton biomass shows a gradualincreasing trend since1981to2011, and biomass increases about165%. Meanwhile, thetemperature of surface water increases about1.80℃among these years, the increase rate is0.06℃/a. Correlation analysis indicates that temperature can affect the interannualchange of phytoplankton biomass, but the effect is not significant.(2) Based on the observations of20cruises from2002to2007and2010to2011,data of temperature, irradiance, dissolved inorganic nitrogen (DIN), dissolved organicnitrogen (DON), PO4-P, dissolved organic phosphorus (DOP) and SiO3-Si were treatedby principal component analysis, and results indicated that the influence of temperatureon the growth of phytoplankton is less than nutrients and irradiance.(3) After the relationship between the Chla and the environmental factors waschanged from nonlinear to linear, the multiple linear regression models of Chla andenvironmental factors was built. Further analysis reveals that the contribution oftemperature to the interannual change of phytoplankton biomass is6.8%, that means thetemperature effect of biomass interannual change is about5.0%/℃, and the annualtemperature effect is about0.3%.2. The effect of temperature on growth of4typical bloom algae in the ChangjiangEstuary and Adjacent Coastal Waters15Ship-based mesocosm/bottle culture field experiments were conducted duringthe field survey in April, May2011and May, June2012, and for comparison, thedominant species were cultured in laboratory.(1) According to results of parallel samples that at the same station and temperature,the experiment precision of field culture experiment is about90.5%±13.4%, equivalentto laboratory culture experiment; however, the recurrence rate is about54.1%±29.8%which is significantly lower than laboratory culture experiment according to results atdifferent stations but with the same dominant algae; but the final results of mesocosmexperiments indicate that the field incubation experiments are more comparable to theactual nature.(2) The growth curves of Prorocentrum donghaiense Lu, Skeletonema, Chaetocerosand Pseudo-nitzschia show “S” type. According to integral biomass within the growthcycle, the temperature effects of the4special bloom algae are9.6%/℃,5.1%/℃,8.2%/℃and4.5%/℃respectively in10～30℃. As a result, the weighted averagetemperature effect of the4algae according to their relative abundance is about5.2%/℃, and well coincides with5.0%/℃which was from the comprehensive statistical analysisof field survey data, hence, the temperature effect of the biomass interannual change inthe Changjiang Estuary and Adjacent Coastal Waters is mainly contributed by this4algae. Further analysis indicates that the temperature effect of dinoflagellate in theChangjiang Estuary and Adjacent Coastal Waters could be represented by the effect ofProrocentrum donghaiense Lu, which is about9.6%/℃; and diatom temperature effectcould be represented by the weighted average temperature effect of the3diatoms, whichis about5.8%/℃.3. The control mechanism of temperature effect on bloom algae growth(1) The growth curves of the4special bloom algae follow the Logistic growthmodel, and its parameters: maximum specific growth rate (μmax) and maximum biomass(Bf) are all affected by temperature. Under the temperature situation of the ChangjiangEstuary and Adjacent Coastal Waters, temperature effect of μmaxand Bffollow the Van’tHoff equation.(2) Based on our analysis and results from published literatures, we suggest that thetemperature effect of μmaxand Bfshould be considered together in ecological dynamicsmodels used to study the areas of the the Changjiang Estuary and Adjacent CoastalWaters. Their quantitative relationship can be described by the Van’t Hoff equation; andfor diatom, the temperature coefficients μmaxof and Bfare0.145±0.108℃-1and0.011±0.026℃-1respectively, and for dinoflagellate the values are0.097±0.059℃-1and0.044±0.001℃-1respectively. This result is quite different from the description oftemperature effect on phytoplankton growth in previous studies, and to validate whichdescription is more reasonable, more field surveys are needed.In summary, focused on the temperature effect of bloom forming phytoplankton, westudy the effect of interannual temperature change on phytoplankton biomass in theChangjiang Estuary and Adjacent Coastal Waters, the temperature effect controlmechanism of typical bloom algae and their relationship, as well as the differencesbetween the field culture experiment and the laboratory culture experiment. This workwill contribute to better understanding the ecological mechanism of the occurrence ofHAB. The major findings of this paper are as following: combined with statistical analysis of on site survey data, Ship-based mesocosm/bottle culture field experimentsand numerical simulation, we found that (1) contrast with previous experiment cultureexperiment, field incubation are more comparable to the actual environmental condition;(2) the temperature effect of biomass interannual change in the Changjiang Estuary andAdjacent Coastal Waters is mainly controlled by Prorocentrum donghaiense Lu,Skeletonema, Chaetoceros and Pseudo-nitzschia and its contribution to the biomasschanges is about7%.