Photosynthesis and growth of Ulva ohnoi and Ulva pertusa (Ulvophyceae) under high light and high temperature conditions, and implications for green tide in Japan

Abstract

SUMMARY The macroalga Ulva ohnoi constitutes a considerable fraction of green tides in coastal areas of Japan, but little is known about the physiological characteristics of this species. To investigate the environmental factors that promote the formation of green tides, we tested the responses of U. ohnoi and another common Japanese species, Ulva pertusa, to various levels of irradiance at different water temperatures. Because the two species are morphologically similar, we identified them using the PCR‐restriction fragment length polymorphism method. Under laboratory conditions, we evaluated the photosynthetic, dark respiration, and relative growth rate at a range of water temperatures (5 to 35°C) and photosynthetically active radiation (0 to 1000 μmol photons m−2 s−1). The maximum gross photosynthetic rate of U. ohnoi was larger than that of U. pertusa. The dark respiration rates revealed no significant differences among the species and temperature conditions. At 500 μmol photons m−2 s−1, the relative growth rate of U. ohnoi was larger than that of U. pertusa in higher temperature and the difference was the largest at 20°C. The estimated compensation irradiance and estimated saturation irradiance of U. ohnoi and U. pertusa ranged from 0.709 to 5.510 and 40.530 to 58.674 μmol photons m−2 s−1, which were lower than those in other intertidal green macroalgae, from 6 to 11 and 50 to 82 μmol photons m−2 s−1, respectively. Thus, U. ohnoi which exists as free‐floating near the water surface and accumulating inside the green tide can survive extensively in the water column of the intertidal zone, furthermore, the species can maintain rapid growth in this situation. Therefore, as a result of this study, it is suggested that the ecological success of U. ohnoi in shallow waters such as the tidal flats, estuarine, and coasts of the inner bay in comparison with U. pertusa.

CULTIVATION OF THE SEAWEED <i>Ulva</i> spp. WITH EFFLUENT FROM A SHRIMP BIOFLOC REARING SYSTEM: DIFFERENT SPECIES AND STOCKING DENSITY

“…Another explanation could be related to the water temperatures to which each species was adapted. It is known that this environmental variable affects the growth rate of seaweeds, with different species exhibiting different optimal temperatures for maximum growth (Mantri et al, 2011;Nakamura et al, 2020). U. ohnoi colleted in the lagoons could have been more adapted to the warmer Table 1.…”

Desempenho de curto prazo de Ulva fasciata produzida em diferentes densidades em Aquicultura multitrófica integrada

“…Entretanto, a Ulva spp. também se mostra extremamente adaptável a condições de menor exposição de luz, como, por exemplo, em florações algais, onde parte dos organismos é exposta a uma grande intensidade de luz e calor na superfície e, em camadas inferiores, a condições de baixíssima luminosidade (Nakamura et al 2020).…”

Evaluating bloom potential of the green-tide forming alga Ulva ohnoi under ocean acidification and warming

“…However, U. ohnoi is a recently reported green-tide-forming species, and research on its ecophysiological responses to physicochemical conditions is very limited (e.g. Mata et al, 2016;Nakamura et al, 2020;Zanolla et al, 2019). This species has been reported to cause widespread green-tides, especially along the coast of Jeju Island, South Korea (Kang et al, 2019), and as the spatiotemporal distributions and intensities of its blooms are increasing, it is becoming more important to better understand their causes and consequences.…”

“…Although U. ohnoi was identified as a new species (Hiraoka et al, 2006), the distribution of this species has already been reported in various region of the world (Guiry and Guiry, 2020), which suggests that U. ohnoi has a strong tolerance to variability in environmental conditions. However, most ecophysiolocial studies on U. ohnoi have focused on the effects of temperature and light intensity (e.g., Mata et al, 2016;Nakamura et al, 2020;Zanolla et al, 2019), and little is known about its tolerance to changes in both seawater temperature and CO 2 (and pH) conditions.…”