PHYTOPLANKTON LIGHT-ABSORPTION AND THE PACKAGE EFFECT IN CALIFORNIA COASTAL WATERS

Phytoplankton absorption spectra were determined for communities collected in the upper euphotic zone over a 250 km transect across a highly variable region of the Southern California Bight. The influence of the 'package effect' on phytoplankton absorption spectra was assessed by comparison of absorption coefficient spectra based on direct measurement with spectral reconstructions calculated from HPLC-determined pigment concentrations. Measurable package effect occurred in less than 25 % of samples, principally from samples taken in the subsurface chlorophyll a maximum layer and in association with populations of large diatoms or dense prymnesiophyte concentrations. Estimates of the package effect in the field derived from these measurements were consistent with the majority of laboratory-determined data for chromophyte and chlorophyte algae. In the cases where reconstructed phytoplankton absorption spectra overestimated measured spectra, the majority of differences could be reconciled by the application of an algorithm calculating the package effect. Where package effects were minimal, reconstructed absorption spectra provided accurate estimates of phytoplankton photosynthetic light absorption without correction for package effects. Existing models for phytoplankton absorption properties will benefit from inclusion of information on the package effect, determined from direct absorption measurements or from information on the taxonomic composition of the phytoplankton community.