Blue Light Photoreactivation in Ultraviolet‐irradiated Young Sporophytes of Alaria Esculenta and Laminaria Saccharina (Phaeophyta)1

Exposure of ultraviolet (UV)‐irradiated young sporophytes of Alaria esculenta (L.) Grev. and Laminaria saccharina (L.) Lamour. to visible light resulted in recovery from UV damage that would otherwise cause much higher mortality. For this photoreactivation, blue light was highly effective, whereas negligible reactivation was produced in green or red light. The blue quantum requirements for a 50% response were 1.9 mol·m−2 in A. esculenta and 1.2 mol·m−2 in L. saccharina, which were comparable to those reported for other blue light responses requiring high energy found in brown algae.