Effects of increased seawater temperature on UV tolerance of Antarctic marine macroalgae

Cold-adapted Antarctic marine macroalgae have different physiological strategies to tolerate the ultraviolet (UV) radiation at low seawater temperatures around 0 A degrees C. The warming of Antarctica's coasts driven by global climate change may alter the physiology such to influence their UV tolerance. This study examined the interactive effects of different seawater temperatures (2 vs. 7 A degrees C) and UV radiation on the physiological performance (primary photochemistry: F (v)/F (m), soluble and insoluble phlorotannins, radical scavenging capacity) of seven macroalgae, which are dominant in Antarctic coastal ecosystems. Four brown and three red macroalgae, collected from Fildes Bay (King George Island, South Shetland Islands) in January/February, were exposed to 6 h of UV/temperature stress, followed by a 16-h recovery. The brown macroalgae Desmarestia menziesii and Ascoseira mirabilis showed the highest UV tolerance at 2 A degrees C, followed by Desmarestia anceps, and the rhodophytes Iridaea cordata, Trematocarpus antarcticus, and Palmaria decipiens. Himantothallus grandifolius (Phaeophyceae) was sensitive to UV radiation at 2 A degrees C. At 7 A degrees C, UV tolerance was improved in UV-sensitive macroalgae probably due to a more efficient damage repair of the photosynthetic apparatus. Temperature, however, did not modulate UV tolerance in D. anceps, indicating an UV-sensitive repair process. Constitutively, high contents of soluble and insoluble phlorotannins and radical scavenging capacities remained unchanged in endemic Desmarestiales. UV induction of soluble phlorotannins along with an increased radical scavenging capacity can be responsible for A. mirabilis' high UV tolerance. This study suggests that UV tolerance in macroalgae, which are sensitive to UV radiation at 2 A degrees C, is modulated by temperature. Enhanced UV tolerance at 7 A degrees C can be apparently ascribed to the stimulation of damage repair of the photosynthetic apparatus rather than to an enhanced UV screening or radical scavenging.