Primary production of crustose coralline red algae in a high Arctic fjord

Crustose coralline algae occupied similar to1%-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) Duwel et Wegeberg 1996 and Phymatolithon tenue (Rosenvinge) Duwel etWegeberg 19961 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 mumol photons.m(-2)-s(-1) and light adaptation (E-k) indices averaging 7-17 mumol photons.m(-2).s(-1). Slight photoinhibition was evident in most plants at irradiances up to 160 mumol photons.m(-2).s(-1). Photosynthetic capacity (Pm) was low, averaging 43-67 mmol O-2.m(-2) thallus-d(-1) (similar to250-400 g C.m(-2) thallus.yr(-1)). Dark respiration rates averaged similar to5 mmol O-2.m(-2) thallus.d(-1). In ice covered periods, Ed at 20 m depth averaged similar to1 mumol photons.m(-2).s(-1),, with daily maxima of 2-3 mumol photons.m(-2.)s(-1). During the open water season, Ed at 20 m depth averaged similar to7 mumol photons.m(-2).s(-1) with daily maxima of similar to30 mumol 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 Pm values, low in situ irradiance, and their relatively low abundance in Young Sound.