Seasonal variation in ecophysiological patterns in macroalgae from an Arctic fjord. II. Pigment accumulation and biochemical defence systems against high light stress

The content of photosynthetic pigments (chlorophyll a, biliproteins, carotenoids) and UV-absorbing mycosporine-like amino acids (MAAs), as well as the activity of reactive oxygen species scavenging enzymes (catalase, superoxide dismutase, glutathione reductase) was investigated in six macroalgal species with respect to the seasonal changes of the solar radiation regime and the macronutrient levels in the seawater of the Kongsfjord (Spitsbergen, Svalbard, Norway). The brown algae Laminaria saccharina, Saccorhiza dermatodea, Desmarestia aculeata; the red algae Palmaria palmata and Devaleraea ramentacea; and one green algal species, Monostroma aff. arcticum, were sampled from the same water depth, before, during and after the break-up of sea ice, first under clear and later under turbid water conditions in late winter, spring and summer 1998. In all species, chlorophyll a (chl a) and total carotenoid content were highest under the sea-ice cover, and decreased gradually upon the sea-ice break-up. Four species showed a subsequent recovery in chl a and total carotenoid concentration in parallel to increasing water turbidity and reduced light availability. In the two red algal species, total phycoerythrin and phycocyanin contents followed a similar trend. Coinciding with the increase in underwater radiation during the sea-ice break-up, both species exhibited a significant increase in the concentration of UV-absorbing MAAs, especially of shinorine and palythine. At the same time, the antioxidative activities of the enzymes superoxide dismutase and catalase in the green and red algae increased, while glutathione reductase activity decreased. Overall, the synthesis of UV-absorbing substances and the increase in the activity of the antioxidative systems in the open-water period imply an increased resistance to high underwater light conditions, including UV radiation. The seasonal changes in pigments and biochemical defence systems may additionally be related to variations in nutrient levels in the seawater. They also reflect the life strategy and the genetic adaptation of the seasonal development to the conditions in the Arctic.