Primary production potential of non-geniculate coralline algae at Cape Evans, Ross Sea, Antarctica

The abundance and photosynthetic characteristics of non-geniculate coralline algae were determined at Cape Evans, McMurdo Sound (Ross Sea), Antarctica, during spring 2003.At the time, the site was covered by 2.5 m of sea-ice through which only 0.48% of incident irradiance was able to penetrate.Coralline algae covered 4 to 60% of the seafloor from water depths of 13 to 26 m.Coralline algal crusts showed light-saturated rates of photosynthesis from 9.4 to 20 mmol O 2 m -2 thallus d -1 and dark respiration rates from 0.15 to 0.96 mmol O 2 m -2 thallus d -1 .The average irradiance at which the onset of light saturated photosynthesis occurred (E k ) was 3.2 µmol photons m -2 s -1 , measured using oxygen micro-electrodes, and 2.9 µmol photons m -2 s -1 , measured using pulse amplitude modulated (PAM) fluorometry techniques.Irradiance at depths of 15 to 20 m did not exceed 2 µmol photons m -2 s -1 during the study, but frequently exceeded the light compensation point for photosynthesis (E c ), estimated as 0.10 µmol photons m -2 s -1 .The effective quantum yield (ΔF/F m ') of Photosystem II, measured in situ over diel periods at depths of 16, 18 and 20 m, averaged 0.691 (SD = 0.003), 0.639 (SD = 0.005) and 0.632 (SD = 0.007), respectively.These values were indicative of minimal down-regulation of photosynthesis, and were consistent with the observation that irradiance never exceeded E k .Laboratory investigations, showed that on transfer from ambient irradiance to 23.5 µmol photons m -2 s -1 , a change of 2 orders of magnitude, the algae showed minimal photoinhibition and a small, but statistically significant increase in E k and maximum electron transport rate.Coralline algae at Cape Evans are able to persist with net carbon accrual under ice, while being able to tolerate periods of higher irradiance during ice-free conditions.This contrasts to Phyllophora antarctica which is dependent on ice-free periods to achieve net production.