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Studying how natural phytoplankton adjust their photosynthetic properties to the quantity and quality of underwater light (i.e. light climate) is essential to understand primary production. A wavelength-dependent photoacclimation strategy was assessed using a multi-color pulse-amplitude-modulation chlorophyll fluorometer for phytoplankton samples collected in the spring at 19 locations across the English Channel. The functional absorption cross section of photosystem II, photosynthetic electron transport (PETλ) parameters and non-photochemical quenching were analyzed using an original approach with a sequence of three statistical analyses. Linear mixed-effects models using wavelength as a longitudinal variable were first applied to distinguish the fixed effect of the population from the random effect of individuals. Population and individual trends of wavelength-dependent PETλ parameters were consistent with photosynthesis and photoacclimation theories. The natural phytoplankton communities studied were in a photoprotective state for blue wavelengths (440 and 480 nm), but not for other wavelengths (green (540 nm), amber (590 nm) and light red (625 nm)). Population-detrended PETλ values were then used in multivariate analyses (partial triadic analysis and redundancy analysis) to study ecological implications of PETλ dynamics among water masses. Two wavelength ratios based on the microalgae saturation parameter Ek (in relative and absolute units), related to the hydrodynamic regime and underwater light climate, clearly confirmed the physiological state of microalgae. They also illustrate more accurately that natural phytoplankton communities can implement photoacclimation processes that are influenced by in situ light quality during the daylight cycle in temporarily and weakly stratified water. Ecological implications and consequences of PETλ are discussed in the context of turbulent coastal ecosystems.

We investigate the relationship between various scattering properties (total, back and side scattering) and Total Suspended Matter (TSM), the dry mass concentration of marine particles in suspension, for coastal and offshore waters in various regions (Coastal Atlantic, Southern North Sea, Mediterranean Sea and French Guyana waters). We quantify the uncertainty on TSM concentration estimation from each scattering property. We further quantify the variability of the total (bp), side (bs) and back scattering (bbp) to mass concentration ratio and explain this variability in terms of the physical (size) and chemical (apparent density, refractive index) properties of the particles. We show that bbp, bp and bs correlate well with TSM (correlation coefficients higher than 0.92), though with considerable scatter along the regression line. We find that 75% of the predicted TSM concentrations from a model based on bs are within 29% of the measured TSM concentration and within 38% and 48% for bbp and bp based models, respectively. The variability of mass specific total scattering (bp*) is mainly explained by total geometric cross section (PSA) and backscattering ratio ( bbp ~ ), with observations above (below) the regression line having significantly higher (lower) bbp ~ and lower (higher) PSA. Variability of mass specific backscattering (bbp*) was smaller and could not be explained by a single parameter. We do find that points below the regression line have significantly lower densities (ρa), PSA, refractive index (n), bbp ~ and chlorophyll a:TSM ratio than points near or above the line. After classification of observations in Case 1 and 2 water types, we find that Case 2 waters (N=149) show significantly higher values of bbp*, ρa, n, bbp ~ and PSA and significantly lower values for bp* and chla:TSM than for Case 1 waters (N=123)., info:eu-repo/semantics/published

Identification of phytoplankton groups from space is essential to map and monitor algal blooms in coastal waters, but remains a challenge due to the presence of suspended sediments and dissolved organic matter which interfere with phytoplankton signal. On the basis of field measurements of remote sensing reflectance (Rrs(λ)), bio-optical parameters, and phytoplankton cells enumerations, we assess the feasibility of using multispectral and hyperspectral approaches for detecting spring blooms of Phaeocystis globosa (P. globosa). The two reflectance ratios (Rrs(490) /Rrs(510) and Rrs(442.5) /Rrs(490)), used in the multispectral inversion, suggest that detection of P. globosa blooms are possible from current ocean color sensors. The effects of chlorophyll concentration, colored dissolved organic matter (CDOM), and particulate matter composition on the performance of this multispectral approach are investigated via sensitivity analysis. This analysis indicates that the development of a remote sensing algorithm, based on the values of these two ratios, should include information about CDOM concentration. The hyperspectral inversion is based on the analysis of the second derivative of Rrs(λ) (dλ2 Rrs). Two criteria, based on the position of the maxima and minima of dλ2Rrs, are established to discriminate the P. globosa blooms from diatoms blooms. We show that the position of these extremes is related to the specific absorption spectrum of P. globosa and is significantly correlated with the relative biomass of P. globosa. This result confirms the advantage of a hyperspectral over multispectral inversion for species identification and enumeration from satellite observations of ocean color. Copyright 2008 by the American Geophysical Union., SCOPUS: ar.j, info:eu-repo/semantics/published