Comparative laboratory study of photoacclimation in selected dinoflagellate and diatom species of the Benguela ecosystem
In their natural environment the diatoms (mixers) are exposed to fluctuations in incident irradiance due to vertical displacements in the water column induced by turbulence whereas the dinoflagellates (migrators and layer-formers) tend to control their vertical positions. In these two groups of phytoplankton physiological acclimation to these fluctuations results in the variation of a number of measurable photosynthetic parameters and variables which can be evaluated in controlled laboratory experiments. The processes can be expressed in time scales from seconds to hours e.g. carbon to chlorophyll ratio changes over several hours. Photoacclimative responses in five species of dinoflagellates (Alexandrium catenella, Protoceratium reticulatum, Prorocentrum micans, Prorocentrum triestinum, Gymnodinium zeta) and three diatom species (Chaetoceros sp., C. capense, C. cf. pendulus) were investigated with respect to parameters of P versus E curves (P*m, Î±* and Ek) and variability in chemical composition (C and N), photosynthetic capacity, pigment ratios, maximum quantum yield and chlorophyll to carbon ratio. These species were grown at irradiances of 33 (LL), 178 (ML) and 647 Î¼mol quanta . m-2 . s-1 (HL) at a 12:12h day: night length at 17 ÂºC. The photosynthetic parameters, pigment concentration and Chl a-specific absorption were mostly affected by photoacclimational status. Species-specific differences were observed at the three different light levels in P versus E curves, pigment concentrations, absorption, carbon to chlorophyll a ratios and quantum yield. Photoprotective carotenoids (diadinoxanthin and diatoxanthin) were significantly different relative to Chl a in eight species of dinoflagellates and diatoms.
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