Patterns and UV sensitivity of carbon anhydrase and nitrate reductase activities in south Pacific macroalgae

This study describes the activities of the key enzymes involved in carbon incorporation (carbonic anhydrase, CA) and inorganic nitrogen reduction (nitrate reductase, NR) in 25 intertidal macroalgae of southern Chile (39°S). UV radiation as a factor affecting the nutrient metabolism of algae was also examined. The results of the enzyme activities and the UV sensitivity were related to the position of the algae on the shore, species/taxonomic groups and morpho-functional patterns. The CA activity in the studied algae ranged from 42 to 165 REA g⁻¹ FW, and was neither related to growing depth nor to taxonomic or morpho-functional groups. The NR activities ranged from 0.1 to 8.9 μmol NO₂⁻ g⁻¹ FW min⁻¹, with the highest levels observed in red algae. In contrast to CA, the NR activities showed a decreasing tendency from supra/midlittoral to infra/sublittoral. Also, differences between morpho-functional groups were seen. The impact of artificial UV radiation on CA and NR activities was variable as in some species it provoked an increase while in other species a decrease was observed, suggesting species-specific responses and UV sensitivity. The CA activity was the most UV sensitive in the taxonomic group Chlorophyta and in the supralittoral algae. The UV sensitivity of NR activity could not be related to any patterns related to morpho-functional or taxonomic groups and habitat depth.