Md. Durand et Rj. Olson, DIEL PATTERNS IN OPTICAL-PROPERTIES OF THE CHLOROPHYTE NANNOCHLORIS SP - RELATING INDIVIDUAL-CELL TO BULK MEASUREMENTS, Limnology and oceanography, 43(6), 1998, pp. 1107-1118
To investigate how cell growth and division affect the optical propert
ies of phytoplankton, cultures of the chlorophyte Nannochloris were sa
mpled over a diel cycle to measure cell size and concentration, light-
beam attenuation and absorption, flow cytometric forward light scatter
ing and chlorophyll fluorescence, and carbon content. Refractive index
was calculated using the anomalous diffraction approximation. At six
different light levels, ranging from 60 to 1,500 mu mol photons m(-2)
s(-1), cell division was tightly phased to the light:dark cycle, occur
ring soon after dark. There were pronounced diel patterns, with minima
near dawn and maxima near dusk, in cell size, cell-specific beam atte
nuation and absorption, flow cytometric forward light scatter, and car
bon content. The diel variations in attenuation cross section were pri
marily caused by changes in cell size due to growth and division, alth
ough there was some influence from changes in refractive index. Becaus
e the major constituents of many phytoplankton communities are small e
ukaryotic cells similar to Nannochloris in cell size and division patt
ern, the results presented here have important consequences for the in
terpretation of diel variations in optical properties observed in the
ocean.