Changes in Thallus Weight and Size in the Green Alga Ulva fenestrata under Artificial Conditions

From August to October 2002, daily measurements of the thallus weight and area were taken in sporophytes and male and female gametophytes of Ulva fenestrata at similar developmental phases. The algae were reared in aquaria at a constant temperature (22 ± 0.5°C); illumination was applied for 12h a day at a photosynthetically active radiation intensity of 400 E/(m² s). All generations showed a linear increase in the thallus weight and area over time with the same relative daily increment (8 to 15%). Generations differed significantly in time to onset of sporogenesis or gametogenesis. The female gametophyte, sporophyte, and male gametophyte began to release gametes or spores in 7, 10, and 15 days, respectively. A scheme for the distribution of cells among age groups is proposed. The scheme seems to account for the linear pattern of thallus growth.