In Potter Cove, Antarctica, newly ice-free areas appeared due to glacial retreat. Simultaneously, the inflow of sediment increased, reducing underwater photosynthetically active radiation (PAR, 400-700 nm). The aim of this study was to determine the photosynthetic characteristics of two macroalgal species colonizing three newly ice-free areas, A1, A2 and A3, with increasing degree of glacial influence from A1 to A3. Turbidity, salinity and temperature were measured, and light attenuation coefficients (Kd) calculated and considered as a proxy for glacial sediment input. The lower depth distribution of the red alga Palmaria decipiens and the brown alga Himantothallus grandifolius was 10 m in A3, 20 m in A2 and 30 m in A1. Both species were then collected, at 5 and 10 m at all areas. Photosynthetic parameters and the daily metabolic carbon balance (CB) were determined. Kd was significantly higher in A3 compared with A1 and A2. The CB of P. decipiens was significantly higher in A1 followed by A2 and A3, and significantly higher at shallower than at greater depth. For H. grandifolius CB was significantly lower in A3 and in A2 at deeper depths compared with the rest of areas and depths. The lower distribution limit of the algae was positively correlated to the light penetration. An increase in the sediment run-off due to global warming might lead to an elevation of the lower depth distribution limit but retreating glaciers can open new space for macroalgal colonization. These changes will probably affect macroalgal primary productivity in Potter Cove with consequences for the coastal ecosystem.
