Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis , the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii , and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa . Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I K values were between 18 and 53 μmol m −2 s −1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I K values between 70 and 74 μmol m −2 s −1 . Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m −2 s −1 . Values of α were high: between 0.4 and 1.1 μmol O 2 g −1 FW h −1 (μmol m −2 s −1 ) −1 in the brown and red algae and between 2.1 and 4.9 μmol O 2 g −1 FW h −1 (μmol m −2 s −1 ) −1 in the green algal species. At 0°C P max values of the brown and red algae ranged from 6.8 to 19.1 μmol O 2 g −1 FW h −1 and were similarly high or higher than those of comparable Arctic‐cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis , 10°C in H. grandifolius , 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata . P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q 10 values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.