SEASONAL VARIATION OF PIGMENTATION OF PERIDINIUM GATUNENSE (DINOPHYCEAE)

Abstract

Yacobi, Y. Z.Israel Oceanographic and Limnological Research, Kinneret Limnological Laboratory, P.O. Box 345, .Tiberias 14102, IsraelPigment composition was measured in natural phytoplankton samples from Lake Kinneret, Israel, dominated by the dinoflagellate Peridinium gatunense. Peak densities were found in April, close to the water surface, with> 109 cells·m‐3, and chlorophyll a concentration of 380 mg·m‐3, and areal chlorophyll a density openface> 1300 mg·m‐2. Cellular concentrations of chlorophyll a changed between 201 and 282 picogram/cell, but did not show a defined temporal fluctuation. The mass ratio of chlorophyll c to chlorophyll a changed from March to June between 0.16 and 0.22, and peridinin to chlorophyll a ratio changed from 0.25 to 0.41. Both of those ratios did not show a clear pattern of seasonal change. On the other hand there was a linear increase of diadinoxanthin and β‐carotene ratios to chlorophyll a throughout the season, parallel to the increase in photon flux density impinging upon the lake surface. Diadinoxantin to chlorophyll a ratio changed from 0.11 to 0.28 and β‐carotene to chlorophyll a ratio varied from 0.03 to 0.08 from March throughout June. Diatoxanthin was not found in natural samples, but could have been induced in controlled experiments, with P. gatunense cultures. Concentration of diatoxanthin increased rapidly, concurrent with a decrease in diadinoxanthin and β‐carotene concentrations, while chlorophyll c and peridinin ratios to chlorophyll a were almost stable with photon flux density increase. The seasonal variation of cellular pigmentation of P. gatunense in Lake Kinneret suggests that accumulation of photoprotective pigments is essential for optimization of photosynthetic activity of that large dinoflagellate.