2015 Volume 10 Issue 3 Pages 154-162
The scattering properties of phytoplankton is one of the main factors needed to model light propagation in the water column. Light scattering by phytoplankton depends on cell size and intracellular materials. In order to characterize the effects, we examined the scattering efficiency of dinoflagellates with large cell sizes and high intracellular carbon contents. Scattering properties of the dinoflagellates Prorocentrum micans and P. minimum were examined in semi-continuous cultures under two light-saturated conditions. Scattering coefficients of the cells at 676 nm (bph[676]) were calculated as the difference between attenuation and absorption coefficients measured using a nine-wavelength absorption-attenuation meter. The bph(676) was normalized to the chlorophyll a (Chl a; b*ph[676]) and cell concentrations (bcell[676]). Lower b*ph(676) and higher bcell(676) were observed for the larger P. micans compared with the smaller P. minimum. The b*ph(676) increased with the ratio of cellular carbon to Chl a (C : Chl a). Both species indicated relatively high C : Chl a compared to other phytoplankton species. A reverse trend of b*ph(676) and bcell(676) between the species could reflect a negative relationship between the equivalent spherical diameter (d) and intracellular Chl a content (Chl ai). A dimensionless efficiency factor for scattering at 676 nm (Qb[676]) was calculated experimentally from d, Chl ai, and b*ph(676). The Qb(676) of both species was two-fold higher than theoretical values based on the anomalous diffraction approximation. The experimentally high Qb(676) might reflect the high b*ph(676). The significant relationship between b*ph(676) and C : Chl a suggests that C : Chl a could be a proxy for scattering efficiency in relation to intracellular materials.
