PRIMARY PRODUCTION OF CRUSTOSE CORALLINE RED ALGAE IN A HIGH ARCTIC FJORD 1

Crustose coralline algae occupied ∼1%–2% (occasionally up to 7%) of the sea floor within their depth range of 15–50 m, and they were the dominant encrusting organisms and macroalgae beyond 20 m depth in Young Sound, NE Greenland. In the laboratory, oxygen microelectrodes were used to measure net photosynthesis (P) versus downwelling irradiance (E d ) and season for the two dominant corallines [ Phymatolithon foecundum (Kjellman) Düwel et Wegeberg 1996 and Phymatolithon tenue (Rosenvinge) Düwel et Wegeberg 1996] representing> 90% of coralline cover. Differences in P‐E d curves between the two species, the ice‐covered and open‐water seasons, or between specimens from 17 and 36 m depth were insignificant. The corallines were low light adapted, with compensation irradiances (E c ) averaging 0.7–1.8 μmol photons·m − 2 ·s − 1 and light adaptation (E k ) indices averaging 7–17 μmol photons·m − 2 ·s − 1 . Slight photoinhibition was evident in most plants at irradiances up to 160 μmol photons·m − 2 ·s − 1 . Photosynthetic capacity (P m ) was low, averaging 43–67 mmol O 2 ·m − 2 thallus·d − 1 (∼250–400 g C·m − 2 thallus·yr − 1 ). Dark respiration rates averaged ∼5 mmol O 2 ·m − 2 thallus·d − 1 . In ice covered periods, E d at 20 m depth averaged ∼1 μmol photons·m − 2 ·s − 1 , with daily maxima of 2–3 μmol photons·m − 2 ·s − 1 . During the open water season, E d at 20 m depth averaged ∼7 μmol photons·m − 2 ·s − 1 with daily maxima of ∼30 μmol photons·m − 2 ·s − 1 . Significant net primary production of corallines was apparently limited to the 2–3 months with open water, and the small contribution of corallines to primary production seems due to low P m values, low in situ irradiance, and their relatively low abundance in Young Sound.