Effects of temperature and irradiance on photosynthesis and growth of a Green-tide forming species (Ulva linza) in the Yellow Sea

Abstract

Samples of the massive drifting green alga, Ulva linza, were collected from the coastal waters of the Yellow Sea, south west of Korea in early July 2009. The effects of various temperature and irradiance levels on the photosynthesis, growth and tissue nutrient content of U. linza were investigated in laboratory for both late stage vegetation (LSV) and the early stage vegetation (ESV) individuals. In the short-term (1 h), acclimation to various irradiance and temperature conditions, maximum gross photosynthetic rate (PBmax), and photosynthetic efficiency ( ) of ESV were significantly higher than those of LSV. Similarly, following long-term (7 d) acclimation to the irradiance and the temperature conditions, gross photosynthetic rate of ESV individuals were also significantly higherthan those of LSV individuals. As a consequence, high photosynthetic rate of ESV individuals induced increases in mass about 60% over the growth saturation irradiance (136 mol photons m-2 s-1) and about 20% under the low temperature conditions (10-15°C) during 7 d acclimation. Because of the high nitrogen utilization efficiency in ESV, U. linza can proliferate quickly in coastal waters of the Yellow Sea. The production and respiration ratios of LSV individuals were low when examined under the temperature and the irradiance conditions that were optimum for ESV growth. Consequently, U. linza exhibits cellular senescence beginning in early July in the Yellow Sea, and green-tides formed by this species cannot be maintained beyond this time.