EFFECT OF SHORT-TERM VARIATION IN IRRADIANCE ON LIGHT-HARVESTING AND PHOTOSYNTHESIS OF THE MARINE DIATOM SKELETONEMA-COSTATUM - A LABORATORY STUDY SIMULATING VERTICAL MIXING

A laboratory study was conducted into the physiology of Skeletonema co statum grown under a simple sinusoidal and a fluctuating light regime. The latter simulated a light regime similar to that which could resul t from the vertical mixing caused by Langmuir circulation. It was show n that the culture simulating vertical mixing reacted by decreasing th e photosynthetic unit (PSU) size and increasing the number of PSUs, an d hence optimized the rate of maximal photosynthesis at high, saturati ng irradiances. This culture also showed some change in photosynthetic parameters during the fight period, which was especially pronounced d uring the shift from a low to a higher irradiance. The effect of this on estimates of primary production in a water column is discussed. Fur ther, it is speculated that the assimilation number is regulated by th e maximum light intensity experienced during the day rather than the t otal daily tight dose, because only the culture submitted to a fluctua ting light regime showed a real change in the maximum rate of photosyn thesis (P(max)B) upon transfer to higher tight levels.