Phytomass and photosynthetically active radiation distribution in the brown alga Cystoseira crinita (Desf.) Bory canopy (the Black Sea) at different time of day

Abstract

Photosynthetically active radiation (PAR) intensity (IPAR) measurements were carried out in a shallow waters section of Tolstiy cape, Sevastopol, the Crimean Peninsula, at a depth of 63 cm along the profile of Cystoseira crinita (Desf.) Bory canopy (canopy height 25-30 cm) at different solar elevation angles in sounding mode on August 27, 2019. During the entire study period the C. crinita thalli were in inclined state. The greater part of the plants mass [67.07% (SD = 9.62, CV = 0.14)] was located in the upper 10 cm layer of the canopy. The PAR vertical intensity profile in the Cystoseira crinita canopy may change during daylight hours. The equations describing the IPAR distribution in the canopy depth at different times of day are provided. Conditions that would typically develop at 9 a.m., made the PAR intensity decrease linearly in the canopy from 657.6 μE . m-2 . s-1 in its upper part up down to 123.45 μE . m-2 . s-1 in its lower part at a depth of 20 cm. At 11 a.m., a high level of PAR intensity (564.98 – 828.12 μE . m-2 . s-1) was observed throughout the canopy. At 6 p.m., with the Sun low on the horizon, the lowest PAR level would be recorded (2.59 – 269.41 μE . m-2 . s-1).