Quantifying phytoplankton communities using spectral fluorescence: the effects of species composition and physiological state

Abstract

In situ fluorometers are the optimal means of providing high-frequency estimates of phytoplankton communities. However, they may be subjected to measurement biases originating from variations in the physiological states of cells, the use of spectral fluorescence signatures (SFS) defined on the basis of inappropriate phytoplankton groups and the lack of linear independence between selected sets of SFS. We assessed correction procedures for measurement biases in mono and mixed cultures of five freshwater phytoplankton species. We investigated the impacts of total Chla levels, the lack of linear independence between SFS and varying physiological states on the accuracy of the Chla estimates that were provided by the FluoroProbe (bbe Moldaenke GmbH, Germany). The use of species-specific SFS allowed for the correction of quantification and classification biases. In some cases, the procedure led to a lack of linear independence between SFS, which significantly reduced estimation accuracies. A convenient method to evaluate linear independence between SFS is provided. Differences in the physiological states of phytoplankton cultures following light pre-acclimation and/or N-starvation appeared to be species specific. Light pre-acclimation led to an underestimation of biomass (up to 228.5%) through fluorescence quenching. The responses of the phytoplankton cultures to N-starvation varied depending on the species (from 240.3 to þ336% biases in Chla quantification). Overall, the application of appropriate corrective measures increased data accuracy. However, optimal data reliability can only be achieved by estimating phytoplankton community composition and associated environmental conditions.

Estimating ecosystem metabolism from continuous multi-sensor measurements in the Seine River

“…The FP used in this study is specifically calibrated with diatoms species of the Seine River that belong to the Bbrown^spectral group (Escoffier et al 2015). Based on this specific SFS, the FP measurements are consistent with the cellular Chla concentrations determined with the spectroscopic reference method.…”

“…Prior to its deployment, the FP was calibrated with two species of Bacillariophyta and Chlorophyta (i.e., Nitzschia palea (Kützing) W. Smith and Pediastrum boryanum (Turpin) Meneghini) representative of the phytoplankton communities of the Seine River. Spectral fluorescence signatures (SFS) were defined for the two species and activated within the device after verifying their linear independence towards other activated SFS (Escoffier et al 2015). In order to assess the device's calibration, grab samples were collected at a monthly to bi-monthly frequency to measure Chla concentrations and perform phytoplankton cell enumerations and biovolume measurements.…”

Chlorophyll a interference in phycocyanin and allophycocyanin spectrophotometric quantification

“…Generally, cyanobacteria contain chlorophyll a (Chla) only together with different carotenoids as accessory pigments: moreover, to maximize the photosynthetic efficiency, they have the phycobiliproteins (chromophore-protein covalently linked compounds). Because only a few other algal classes (rhodophytes and cryptophytes) possess these pigments, they can be used as a valuable proxy to detect the presence of cyanobacteria in mixed phytoplankton assemblages (Seppälä et al, 2007;Escoffier et al, 2015).…”

Improving the Remote Sensing Retrieval of Phytoplankton Functional Types (PFT) Using Empirical Orthogonal Functions: A Case Study in a Coastal Upwelling Region

“…This is a desirable characteristic that allows a direct estimation of the degree of local spectral dominance without the requirement of bio-volume transformations from biomass information. Previous studies on the comparison of different techniques for assessing phytoplankton community structures have shown that FluoroProbe is potentially capable of determining its general characteristics when compared to HPLC analyses [47][48][49]. However, its application improves greatly when species-specific calibrations under different environmental conditions are considered [49].…”

“…Previous studies on the comparison of different techniques for assessing phytoplankton community structures have shown that FluoroProbe is potentially capable of determining its general characteristics when compared to HPLC analyses [47][48][49]. However, its application improves greatly when species-specific calibrations under different environmental conditions are considered [49]. In the case of the FluoroProbe data used in this study, a comparison of the Chl-a estimates with those obtained from fluorometric analyses revealed very similar patterns of distribution, though the magnitudes were higher in the first case.…”