Factors Regulating the Relationship Between Total and Size-Fractionated Chlorophyll-a in Coastal Waters of the Red Sea.
AuthorsBrewin, Robert J W
Moran, Xose Anxelu G.
Raitsos, Dionysios E
Gittings, John A
Calleja Cortes, Maria de Lluch
Ansari, Mohd Ikram
Al-otaibi, Najwa Aziz
Huete-Stauffer, Tamara M
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
Marine Science Program
Red Sea Research Center (RSRC)
Department of Earth Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
Water Desalination and Reuse Research Center (WDRC)
Division of Biological and Environmental Sciences and Engineering, Red Sea Research Center, King Abdullah University for Science and Technology, Thuwal, Saudi Arabia.
Earth Science and Engineering Program
Physical Sciences and Engineering (PSE) Division
KAUST Grant NumberREP/1/3268-01-01
Permanent link to this recordhttp://hdl.handle.net/10754/658589
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AbstractPhytoplankton biomass and size structure are recognized as key ecological indicators. With the aim to quantify the relationship between these two ecological indicators in tropical waters and understand controlling factors, we analyzed the total chlorophyll-a concentration, a measure of phytoplankton biomass, and its partitioning into three size classes of phytoplankton, using a series of observations collected at coastal sites in the central Red Sea. Over a period of 4 years, measurements of flow cytometry, size-fractionated chlorophyll-a concentration, and physical-chemical variables were collected near Thuwal in Saudi Arabia. We fitted a three-component model to the size-fractionated chlorophyll-a data to quantify the relationship between total chlorophyll and that in three size classes of phytoplankton [pico- (<2 μm), nano- (2-20 μm) and micro-phytoplankton (>20 μm)]. The model has an advantage over other more empirical methods in that its parameters are interpretable, expressed as the maximum chlorophyll-a concentration of small phytoplankton (pico- and combined pico-nanophytoplankton, Cpm and Cp,nm , respectively) and the fractional contribution of these two size classes to total chlorophyll-a as it tends to zero (D p and D p,n ). Residuals between the model and the data (model minus data) were compared with a range of other environmental variables available in the dataset. Residuals in pico- and combined pico-nanophytoplankton fractions of total chlorophyll-a were significantly correlated with water temperature (positively) and picoeukaryote cell number (negatively). We conducted a running fit of the model with increasing temperature and found a negative relationship between temperature and parameters Cpm and Cp,nm and a positive relationship between temperature and parameters D p and D p,n . By harnessing the relative red fluorescence of the flow cytometric data, we show that picoeukaryotes, which are higher in cell number in winter (cold) than summer (warm), contain higher chlorophyll per cell than other picophytoplankton and are slightly larger in size, possibly explaining the temperature shift in model parameters, though further evidence is needed to substantiate this finding. Our results emphasize the importance of knowing the water temperature and taxonomic composition of phytoplankton within each size class when understanding their relative contribution to total chlorophyll. Furthermore, our results have implications for the development of algorithms for inferring size-fractionated chlorophyll from satellite data, and for how the partitioning of total chlorophyll into the three size classes may change in a future ocean.
CitationBrewin, R. J. W., Morán, X. A. G., Raitsos, D. E., Gittings, J. A., Calleja, M. L., Viegas, M., … Hoteit, I. (2019). Factors Regulating the Relationship Between Total and Size-Fractionated Chlorophyll-a in Coastal Waters of the Red Sea. Frontiers in Microbiology, 10. doi:10.3389/fmicb.2019.01964
SponsorsThe authors would like to acknowledge all scientists and crew involved in the collection of the in situ data used in this manuscript. We thank Trevor Platt for providing helpful comments on our manuscript. Funding. This work was funded by the King Abdullah University for Science and Technology (KAUST) Office of Sponsored Research (OSR) under the Virtual Red Sea Initiative (Grant # REP/1/3268-01-01). This work was also supported by the UK National Centre for Earth Observation (NCEO).
PublisherFrontiers Media SA
JournalFrontiers in microbiology
CollectionsArticles; Biological and Environmental Sciences and Engineering (BESE) Division; Red Sea Research Center (RSRC); Bioscience Program; Marine Science Program; Physical Sciences and Engineering (PSE) Division; Earth Science and Engineering Program; Water Desalination and Reuse Research Center (WDRC)
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