Diurnal Variation in Pigment Content in Porphyra laciniata and Chondrus crispus and its Relation to the Diurnal Changes of Underwater Light Quality and Quantity

Abstract

Abstract. Short‐term diurnal changes in the pigment content of two red algae, Porphyra laciniata and Chondrus crispus, in their natural environment (Helgoland, North Sea) were detected. Simultaneously, diurnal variations in underwater light quality and quantity were analyzed. A relation between rapid changes in pigment content at twilight and drastic changes in certain wavelength bands: red: far‐red, green: red, and blue: red was observed. Through these ratios, which were detected by various photoreceptor systems, the algae were able to modulate the pigment content during the course of the day.SummaryDiurnal changes in the total photosynthetic pigment (chlorophyll a and biliprotein) contents and pigment ratios of the red algae Porphyra laciniata growing at 0.5 m and 3.5 m and Chondrus crispus at 2‐2.5 m under natural conditions in Helgoland (North Sea) in July 1990 have been observed.The underwater light quality and quantity, the attenuation coefficient (K) in some wavebands, and the ratios: red: far‐red (R: FR), green: red (G: R), and blue: red (B: R) throughout the day and at different depths (0.5, 1, 1.5, 2.5, and 3.5 m) were measured at the same time as the pigment contents. At twilight, rapid quality changes were observed. Directly after this period, major pigment changes in Porphyra and Chondrus were detected.Drastic changes in the pigment content in Porphyra laciniata at twilight, immediately after this period, and after noon were observed. The pigment content of plants growing at 0.5 m and plants transplanted to 3.5m were significantly different (P <0.05). Porphyra at 3.5m had higher PE/PC and PE/Chl a ratios than at 0.5 m. The maximum biliprotein level was observed immediately after noon. The algae growing at deeper levels produced more biliprotein in response to a simultaneous decrease in light intensity and an increase in the G: R ratio. In addition, at dawn, an “inverse chromatic adaptation” was observed, since PE/PC and PE/Chl a ratios during this period decreased when G/R increased.In Chondrus crispus, diurnal Chl a variations showed a reverse pattern in relation to biliprotein variations: the biliprotein content increased during daylight, while Chl a decreased. Maximum PE and PC was produced after noon. The biliprotein: Chl a ratio showed a clear circadian rhythm.The changes in R: FR, G: R, and B: R ratios are proposed as being “photomorphogenic signals” which control the pigment content in algae. Because R: FR and G: R ratios increase linearly with depth, the detection of light quantity changes through these ratios is proposed.