Effects of irradiance on pigment signatures of harmful algae during growth process

Three harmful algal bloom （HAB） species, Phaeocystis globosa, Thalassiosira rotula, and Prorocentrum donghaiense were isolated from the coast of China and cultured in batches at three light intensities （40, 70 and 150 μmol photons · m -2 · s -1 ）. The variation patterns of cell numbers and growth rates with light intensity during growth process were different among species. In P. globosa and T. rotula, maximum growth rates were found at 150 μmol photons · m -2 · s -1 and ranged from 0.60 divisions per day in T. rotula, to 1.17 divisions per day in P. globosa. The highest growth rate of P. donghaiense, however, was found at 70 μmol photons · m -2 · s -1 （0.36 divisions per day）. In general, all the three HAB species showed adaptation to increasing light intensity by decreasing cellular concentrations of chlorophyll a （Chl a）, but the variation patterns during the growth process were species-specific. The cellular concentrations of Chl a in P. donghaiense and T. rotula increased gradually with incubation time, but the opposite trend was found in P. globosa. Most of the pigment ratios and pigment indices of these three species were nearly constant during the growth process and showed small changes at different light intensities illustrating the applicability of chemotaxonomy during the initial and developing stages of HAB events, which is very important to study the ecological issues related to HAB species. Ratios of photoprotective carotenoids, such as diadinoxanthin, diatoxanthin and β, β-carotene to total chlorophylls a （Tchl a） showed the trend of increasing with the increase of light intensity during growth process. The species-specific and pigment-specific variations in pigment ratios/indices at different light intensities during growth process probably reflected the differences in the pigment composition as well as the adaption capabilities of different species to the changes of physical conditions.

The modification and optimizing of the CHEMTAX running in the South China Sea

In order to determine the phytoplankton community composition, the modification and optimizing of the CHEMical TAXonomy（CHEMTAX） running was carried out through samples grouping, successive run and evaluate the results for HPLC-pigment samples in the South China Sea（SCS）. The vertical distribution of the ratio of pigment to total Chl a（TChl a） exhibited three different patterns, including increasing with depth pattern（e.g., But-Fuco）, decreasing with depth pattern（e.g., Zea） and increasing at deep chlorophyll maximum（DCM） pattern（e.g., Hex-Fuco）. The vertical profiles for Fuco/TChl a and Pras/TChl a was higher in coast than in the shelf and basin, and the Zea and Dv-Chl a expressed conversely. So the samples in the coastal stations must be separated for the cluster analysis group procedure in the SCS. Successive run was introduced into the CHEMTAX calculation and the output results were evaluated by the convergence of pigment/TChl a ratios. Most of the ratios were well converged at the fifth running, except Zea/TChl a for Prochlorococcus and Chl b/TChl a for prasinophytes and so on. To evaluate the fifth running＇s results, haptophytes_8 and chlorophytes were two phytoplankton groups with much uncertainty. But the fifth estimated value was better than running once was supported by the regression evidence between the measured pigment concentration and calculation values. Synechococcus was another component with much mutability, and the CHEMTAX＇s result should be compared to the flow cytometry＇s cell abundance.