Effects of water temperature, light and nitrate on the growth of sporelings of the non-geniculate coralline alga Lithophyllum okamurae (Corallinales, Rhodophyta)

Coralline algae in temperate waters commonly form an understory beneath canopy-forming seaweeds. They are sometimes dominant on barren grounds where seaweed forests have declined. The early life history stage such as a sporeling is a crucial phase for the initial establishment and persistence of the seaweed population. Therefore, the optimum and vital growth conditions for sporelings of these coralline algae under various environmental factors must be defined. We investigated using laboratory culture the effects of water temperature, light, and nitrate levels on the growth of sporelings of a non-geniculate coralline alga Lithophyllum okamurae which is commonly found in the temperate Western Pacific. The optimum temperature for growth of the sporelings was 20 °C, with the growth rate decreased above this temperature. The highest temperature L. okamurae sporelings survived was 30 °C. The saturating irradiance (photosynthetic photon flux density) for the growth of the sporelings was inferred as approximately 130 μmol photons m−2 s−1 with photoinhibition observed at a greater irradiance, which was similarly seen in other coralline algae grown in shade conditions, indicating that L. okamurae had adapted to such conditions. The initial slope of the growth rate versus nitrate concentration (Vmax/Ks) of the sporelings was lower than that of other coralline species, but was similar to values for other macroalgae. These results indicate that L. okamurae is not more tolerant than other macroalgae under these mentioned growth conditions; hence, this species might respond similarly as other macroalgae against future environmental changes.