@ 1983, 1) ~ the American Sacicty of Limnology Inc. Optical efficiency factors of some phytoplankter+

Absorption and total scattering coefficients of four phytoplankton species grown in batch cultures were measured simultaneously. Backscattering coefficients were obtained by using an integrating sphere. These coefficients are transformed into specific coefficients, i.e. related to a unit of concentration in chlorophyll a, and also into dimensionless efficiency factors characteristic of the cells. The specific coefficients differ noticeably from one species to another. Total scattering and backscattering coefficients are clearly depressed near and inside the absorption bands. These minima can be interpreted by combining the theory of anomalous dispersion with Mie-Lorentz theory applied to polydisperse suspensions. The backscattering efficiency (ratio of backscattering to total scattering) of algal cells appears to be very low (typically ~0.1%). These different results must be taken into consideration when interpreting and modeling the optical properties of seawater, particularly ocean color. They also must be considered when modeling photosynthesis, since the variations in the light-harvesting ability of the cells intervene directly in the quantum yield estimate. The optical properties of natural waters depart from those of ideally pure water because of the presence, in variable amounts, of diverse dissolved and partic-ulate substances. From an optical point of view, these can be considered as be-longing to four groups: live algal cells; biogenous detritus associated with and deriving from these algae; terrigenous particles and resuspended sediment; and dissolved organic (yellow) substances. Of these, phytoplankton, as the only primary producer in the pelagic environment, is of particular interest. In addition, the al-gal cells and their debris predominantly determine the optical properties of the water in the open sea, away from land and bottom influence. Depending on the physiological state of the algae and on environmental con-ditions, primary production is effected through photosynthesis, with a varying yield. Such a yield, estimated on a quan