Optimizing temperature, light intensity, and salinity conditions for the culture of an asexual population of Ulva ohnoi

Abstract

Ulva ohnoi forms harmful green tides and a large population has recently been recorded in Zhanjiang, China, where its strong growth and reproduction favor its large-scale commercial cultivation. Understanding its biology at different growth stages is essential to maximize its aquaculture potential. We first confirmed the generational identity of our samples to eliminate potential biological variations due to generation type. We used an orthogonal experimental approach to investigate three factors (temperature, light intensity, and salinity) at three different levels, to identify optimal cultivation conditions for each developmental stage, and documented the maturation and early development processes. All of our samples were female gametophytes or apomicts, which produced biflagellate female gametes or apomictic zoids, without undergoing sexual reproduction. The optimal growth conditions for U. ohnoi from Zhanjiang were 20 °C, 90 μmol·m⁻²·s⁻¹ light intensity, and 25 salinity; the optimal reproductive conditions were 25 °C, 60 μmol·m⁻²·s⁻¹ light intensity, and 35 salinity; and the optimal development conditions were 25 °C, 90 μmol·m⁻²·s⁻¹ light intensity, and 25 salinity. Temperature dominated in determining U. ohnoi from Zhanjiang growth and early development, while light intensity was most influential in governing reproduction. Growth, reproduction, and early development were almost unaffected by salinity values between 15 and 35. These findings provide essential baseline information for the large-scale aquaculture of U. ohnoi in the coastal waters of southern China.