Pigment-and chromoprotein-dependent spectral models, designed to accurately reconstruct whole cell absorption spectra for photosynthetic dinofldgellates, were assessed. Measured spectral absorption properties (400 to 700 nm) included signatures from whole cells, dispersed thylakoid fragments (unpacked absorption), isolated chromoproteins and individual pigments from high (500 pm01 m-2 S-') and low (35 pm01 m-2 S") light-adapted cells of the dinoflagellates Prorocentrum minimum and Heterocapsa pygmaea grown in continuous light at 15 OC. For model verification, we also developed a procedure to measure unpackaged cell absorption, free of solvent and light-scattering effects. Maximum measured chl a-spec~f~c absorption at 675 nm appears to be closer to 0.027 than a predicted value of 0.0203 m2 mg-l chl a based on absorption from chl a in 90% acetone. The percent fractional absorption of 'in vivo' welght-specific absorption coefficients of individual pigments relative to total weighted absorption (all pigments) was estimated to indicate the light-harvesting capabilities of the different pigments as a function of photoadaptive status and water color. Correspondingly, the weighted absorption of each pigment fraction has been estimated in theoretical white light and in 'clearest' green coastal and blue oceanic waters. Independent of water color, peridinin was by far the most important light-harvesting pigment, followed by chl c2 and chl a. The photoprotective diadinoxanthin absorbed most efficiently in the blue part of the visible spectrum. Results indicate that the chromoprotein model (1) overcame spectral distortions inherent in more general pigment-dependent models and, when combined with corrections for pigment packaging effects. (2) provided accurate spectral estimates of in vivo absorption coefficents and (3) worked equally well for dinoflagellate species with or without the major light-harvesting peridinin-chlorophyll-protein complex, PCP. Findings are discussed in the context of modeling of blo-optical characteristics in dinoflagellates, their photoecology and implications for the in situ optical monitoring of red tides.

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 maxin~um layer and in association with populat~ons of large diatonls or dense pryn~nesiophyte concentrations. Estimates of the package effect in the field derived from these measurements were consistent wlth the majority of laboratory-determined data for chromophyte and chlorophyte algae. In the cases where reconstructed phytoplankton absorptlon spectra overestimated measured spectra, the majority of differences could be reconclled by the application of a n algorithm calculating the package effect. Where package effects were minlmal, reconstructed absorption spectra provided accurate estimates of phytoplankton photosynthetic light absorptlon without correction for package effects. Existing models for phytoplankton absorption properties will benefit from inclusion of information on the package effect, determined from dlrect absorption measure~nents or from information on the taxonomic composltlon of the phytoplankton community.

Growth and absorption properties of the marine dinoflagellate Heterocapsa pygrnaea (also known as Glenodinium sp.) were defined for batch cultures of populations grown in blue and green light. Log-phase cells exhibited variations in growth rate, cell volume, pigmentation, chlorophyllspecific absorption, absorption cross-sections for photosynthesis and cellular packaging effects that were dependent upon spectral growth irradiances (5 to 150 ,uEin m-2 S-'). By combining knowledge of (1) cellular pigmentation, (2) the distribution of specific pigments into discrete light-harvesting components, and (3) newly-derived pigment-specific absorption coefficients for the major pigment-protein complexes in dinoflagellates, it was possible to reconstruct the photosynthetic absorption properties of the dinoflagellate. The degree of fit between measured and reconstructed absorption spectra varied a s a function of spectral growth irradiance. In most instances, the majority of the discrepancy was attributable to a wavelength-dependent package effect, which ranged from 1 to 30 % depending upon growth irradiance control of cell pigmentation and cell volume. Preliminary results contribute to the development of a model which uses field measurements of pigmentation and cell characteristics to monitor the presence, distribution, and bio-optical properties of red-tide dinoflagellates.

The aim of this study was to quantify the variability in and differences between spectral and nonspectral measurements: of light utilization efficiencies for natural phytoplankton communities, in order to evaluate possible consequences for blo-opt~cal models of in s j t~l p]-1ma1-y production (P). Field samples were collected at 4 coastal stations durlng a 1 d transect (July 23, 1988) and productivity P(AA,,z) were derived. Significant spatial variability in all bio-optical parameters was noted for communities in the surface waters and the chlorophyll maximum. For surface waters, there was significant variability in the 525 to 600 nm region of the spectral signatures of dl[dA,,z) and P(AA,,z) which was attributable to phycobilins not resolved In absorption spectra. The importance of light absorption by photosynthetic pigments other than chlorophyll a (chl), and thcir assoc~ated Impact upon absorption-based production parameters, increased w~t h light depth. One consequence was a close correspondence between AQ,, and P(AA,,z) at depth w h~c h was not evident in surface waters A second consequence was that while spectrally weighted and whlte l~g h t estimates of quantum yield were occasionally sim~lar In surface waters, spectral estimates for all chlorophyll maximum communities were 4-to 6-fold higher than white light measurements. Results confirm previous observations that white light measures of quantum yield can significantly underestimate quantum yield for subsurface communities of phytoplankton (Prezelin e t al. 1989) a n d provide a conceptual base on which to improve existing and future spectral models of in situ photosynthetic quantum yield.

The impact of blue-green light incubation on short-term diurnal, daily, and integrated water column estimates of whole water (> 0.2 pm) and Synechococcus-specific photosynthesis was assessed throughout the euphotic zone at 2 stations in the Sargasso Sea. Replicate samples were incubated under both tungsten white Light and broad band blue-green light, where the latter simulated light quality within the upper water column of the open sea. Diurnal variations in size-fractioned (0.2-0.6 pm, 0.6-1 km, and 1-5 pm) blue-green vs white light photosynthesis-irradiance (P-I) curves, chlorophyll (Chl) and phycoerythrin (PE) concentrations, and cell abundance of PE-rich cyanobacterial Synechococcus spp. and Chl-fluorescing algae, were measured within samples from the surface, PE maximum, Chl maximum, and the base of the euphotic zone. Synechococcus spp. dominated ultraphytoplankton communities down to the light depths of the PE maximum (3 to 7 % surface illumination, I,), with maxima in cell abundance routinely located at Light depths 2 50 % I , . Blue-green and white light incubation conditions generally did not affect light-saturated rates of photosynthesis (P, , ) but blue-green light routinely did provide much higher estimates of light-limited rates of photosynthesis (alpha). For size-fractioned subpopulations dominated by Synechococcus spp., blue-green hght values of alpha were 25-fold greater than wlute light estimates. Compared to white light estimates, bluegreen light estimates of total (> 0.2 pm) daily integrated water column primary productivity were 6 to 13 % higher, while the contribution of Synechococcus spp. to overall primary production rose from between 57 and 61 % to between 73 and 84 %. From the surface down to about 5 % I,, the PE content of Synechococcus cells increased with decreasing light and/or increasing inorganic nitrogen availability. Increases in Synechococcus PE/cell occurred in direct proportion to blue-green light measurements of photosynthetic quantum efficiency, further indicating that these cyanobacteria are physiologically well suited to harvest photosynthetically utilizeable light throughout a large portion of the euphotic zone.