Using a two-layered sphere model to investigate the impact of gas vacuoles on the inherent optical properties of <i>Microcystis aeruginosa</i>

Abstract

Abstract.A two-layered sphere model is used to investigate the impact of gas vacuoles on the inherent optical properties (IOPs) of the cyanophyte Microcystis aeruginosa. Enclosing a vacuole-like particle within a chromatoplasm shell layer significantly altered spectral scattering and increased backscattering. The two-layered sphere model reproduced features in the spectral attenuation and volume scattering function (VSF) that have previously been attributed to gas vacuoles. This suggests the model is good at least as a first approximation for investigating how gas vacuoles alter the IOPs. Measured R rs was used to provide a range of values for the central value of the real refractive index, 1 + , for the shell layer using measured IOPs and a radiative transfer model. Sufficient optical closure was obtained for 1 + between 1.1 and 1.14, which had corresponding Chl a-specific phytoplankton backscattering, b * bφ , between 3.9 and 7.2 × 10 −3 m 2 mg −1 at 510 nm. The b * bφ values are in close agreement with the literature and in situ particulate backscattering measurements. R rs simulated for a population of vacuolate cells was greatly enlarged relative to a homogeneous population. A sensitivity analysis of empirical algorithms for estimating Chl a in eutrophic/hypertrophic waters suggests these are robust under variable constituent concentrations and likely to be species-sensitive. The study confirms that gas vacuoles cause significant increase in backscattering and are responsible for the high R rs values observed in buoyant cyanobacterial blooms. Gas vacuoles are therefore one of the most important bio-optical substructures influencing the IOPs in phytoplankton.

The Fundamental Contribution of Phytoplankton Spectral Scattering to Ocean Colour: Implications for Satellite Detection of Phytoplankton Community Structure

“…The resulting IOPs are presented, with explanatory notes, in Appendix A.2. (A cyanobacterial group with substantially altered geometry to represent vacuolated cells has also been developed [63]).…”

“…The EAP model has been used for a variety of applications [35,37,63,64]. It can be assumed that a model demonstrated as successful in phytoplankton-dominated waters [65] addresses the phytoplankton component accurately.…”

Characterization of Intracellular Structure Changes of Microcystis under Sonication Treatment by Polarized Light Scattering

“…The biological characteristics of cyanobacteria interact with the light field through scattering and absorption processes [11,12]. The intracellular gas vesicles of cyanobacteria cells are significant bio-optical substructures [13,14], and potentially are one of the most important distinctive cellular structures influencing the optical properties [15].…”

Quantification of Phycocyanin in Inland Waters through Remote Measurement of Ratios and Shifts in Reflection Spectral Peaks

“…These characteristics of the spectral peak can be particularly useful for estimating cyanobacterial biomass because backscattering can be greater for cyanobacteria, especially Microcystis, the most common and problematic cyanobacterial species, owing to their spherical shape, small size, and the presence of internal gas vacuoles [28,29]. Moreover, absorption in water dominated by small-sized cyanobacteria can be higher than that in water dominated by large-sized eukaryotic phytoplankton with the same level of chlorophyll [30].…”