A TECHNIQUE FOR THE ESTIMATION OF INDICES OF REFRACTION OF MARINE PHYTOPLANKTERS’

Measurements of light scattering and particle size distribution wcrc pcrformcd on a growing culture of the unicellular phytoplankter Isoch~ysis gnlbnnn. The culture rcprcscntcd a narrow, polydispcrsc distribution of nearly spherical particles. Assuming the culture to bc homogcncous in rcfractivc index, a tcchniquc was dcvclopcd that provided an cstimatc of the index of refraction of the culture for the wavclcngths 5,460 A and 5,780 A. The rclativc index of refraction (relative to that of seawater) of the culture varied with time From 1.026 to 1.036 over a l2-day sampling period and sccmcd to bc rclatcd to changes in the surface area: vohmle ratio of the cells. The indicts of refraction detcrmincd using green light (5,460 A) corresponded closely with those found using yellow (5,780 A), with slight fluctuations perhaps due to changes in ccl1 pigmentation ratios