DIEL VARIATIONS IN OPTICAL PROPERTIES OF MICROMONAS PUSILLA (PRASINOPHYCEAE)¹

Abstract

Micromonas pusilla (Butcher) Manton et Parke, a marine prasinophyte, was used to investigate how cell growth and division affect optical properties of phytoplankton over the light:dark cycle. Measurements were made of cell size and concentration, attenuation and absorption coefficients, flow cytometric forward and side light scattering and chl fluorescence, and chl and carbon content. The refractive index was derived from observations and Mie scattering theory. Diel variations occurred, with cells increasing in size, light scattering, and carbon content during daytime photosynthesis and decreasing during nighttime division. Cells averaged 1.6 μm in diameter and exhibited phased division, with 1.3 divisions per day. Scattering changes resulted primarily from changes in cell size and not refractive index; absorption changes were consistent with a negligible package effect. Measurements over the diel cycle suggest that in M. pusilla carbon‐specific attenuation varies with cell size, and this relationship appears to extend to other phytoplankton species. Because M. pusilla is one of the smallest eukaryotic phytoplankton and belongs to a common marine genus, these results will be useful for interpreting in situ light scattering variation. The relationship between forward light scattering (FLS) and volume over the diel cycle for M. pusilla was similar to that determined for a variety of phytoplankton species over a large size range. We propose a method to estimate cellular carbon content directly from FLS, which will improve our estimates of the contribution of different phytoplankton groups to productivity and total carbon content in the oceans.

Inferring phytoplankton carbon and eco-physiological rates from diel cycles of spectral particulate beam-attenuation coefficient

“…From this figure it is evident that the model ascribes the observed increase in c p during the illuminated part of the day to an increase in cellular scattering, rather than cell abundance (compare Fig. 6a and b), as suggested by previous studies (e.g., Stramski et al, 1995;DuRand et al, 2002). The c p dynamics at night are instead related to both variations in cell abundance and scattering cross-section (Fig.…”

“…Two field studies showed that ξ decreased during the day and increased at night suggesting that the relative size of the particles affecting c p increased during the day and decreased at night (Oubelkheir and Sciandra, 2008;Slade et al, 2010). Laboratory studies have also shown diel variability in ξ (Claustre et al, 2002;DuRand et al, 2002;Stramski and Reynolds, 1993;Stramski et al, 1995), but only DuRand et al (2002) clearly reported that the spectral slope of the scattering coefficient decreased during the day and increased at night as recently observed in the field.…”

“…Cell cycle synchronization to light availability has also been observed in larger phytoplankton, such as diatoms (Vaulot et al, 1986;Stramski and Reynolds, 1993), although these larger organisms are also known to be able to divide more than once per day (Chisholm and Costello, 1980). Second, diel variations in c p are more correlated to changes in scattering cross-section (σ b , a measure of the light scattered by a single cell), than to changes in cell concentration (Stramski and Reynolds, 1993;Stramski et al, 1995;DuRand et al, 2002) and σ b appears to vary mostly with changes in cell size DuRand and Olson 1998, but see Stramski and Reynolds, 1993).…”

The measurement of phytoplankton biomass using flow‐cytometric sorting and elemental analysis of carbon

“…Carbon (pg C cell Bertilsson et al 2003, Heldal et al 2003, and Verity et al 1992 Values taken or calculated from Johnson et al 2009, Durand et al 2002, and Montagnes et al 1994 Values taken or calculated from Waite et al 1997 andMontagnes et al 1994. Table 2 for references.…”

Carbon to volume relationship of Isochrysis galbana (Prymnesiophyceae) during cell divisions

“…Previously published data on maxima and minima in either cell volume or carbon quota during cell divisions of nanophytoplankton were obtained from the following sources: Eppley & Coatsworth (1966), Kohata & Watanabe (1986, Berdalet et al (1992), DuRand & Olson (1998), Varela & Harrison (1999), DuRand et al (2002, and Ohi et al (2002Ohi et al ( , 2003. From these sources, we selected the data giving both the cell volume and carbon quota during cell division: Kohata & Watanabe (1989), DuRand & Olson (1998), Varela & Harrison (1999) and DuRand et al (2002).…”