Impact of ultraviolet radiation on physiology and development of zoospores of the brown alga Alaria esculenta from Spitsbergen

doi: 10.1111/j.1399-3054.2007.00923.x Zoospores of the brown alga Alaria esculenta from Spitsbergen were exposed in the laboratory to photosynthetically active radiation [(P), 400–700 nm], P1 UVA radiation (PA, 320–700 nm) and PA1UVB radiation (PAB, 280–700 nm). Germination rates were determined, and the germination process was documented by light microscopy. In parallel, the presence of UV-absorbing phlorotannins was studied. Photoinhibition and recovery of photosynthesis were monitored as well as DNA damage and repair. After 8 h of exposure to PAB, germination was inhibited. A 16-h exposure to PA and PAB resulted in a dramatic reduction of germination rates. Phlorotannin-containing physodes were observed in the peripheral cytoplasm and physode-like bodies were found outside the spore, still attached to the zoospore as well as freely floating in themedium; this suggested exocytosis. The absorbance of spore suspensions below 300 nmwas higher after 20 h exposure to P, PA and PAB comparedwith the dark treatment. About 50%of the radiationwas absorbed by the zoospores, and the rest was absorbed by the medium, especially after PA and PAB exposure. In this way, harmful UV radiation is absorbed before reaching the cells and this is probably the major reason for the relatively low DNA damage after !8 h exposure to PAB. Under these conditions, DNA damage was efficiently repaired and there was a notable recovery of photosynthesis. However, after 16 h exposure to PA and PAB, the protective and repair mechanisms are surcharged and the zoospores degenerate. The results cast light on the potential impact of enhanced UVB radiation on a dominant component of the seaweed community on Spitsbergenbecause of stratospheric ozone depletion. The acclimation potential of zoospores of this species to UV radiation as demonstrated here is regarded as conferring a competitive advantage in recruitment over similar species in the upper sublittoral zone.