A Warmer Arctic Compromises Winter Survival of Habitat-Forming Seaweeds

Continuous winter darkness at a latitude of 79 degrees N was simulated in cultures of four species of Arctic seaweeds at 3 and 8 degrees C. The laminarians Saccharina latissima and Alaria esculenta, and the rhodophytes Phycodrys rubens and Ptilota gunneri were monitored for 4 months in total darkness and after 1 week following light return in early spring, under controlled laboratory conditions. Biomass loss during darkness was enhanced by the high temperature in all species. At 8 degrees C, the two laminarians were unable to resume growth upon re-illumination. Alaria esculenta showed new blade production by the end of the dark period, but only at 3 degrees C. In all species, the photosynthetic ability was sustained, not suspended, during the whole dark period. P. rubens exhibited lower photosynthetic potential at 8 degrees C than at 3 degrees C during the darkness period, but it was able to recover its O-2 evolving potential upon re-illumination, as P. gunneri and S. latissima did, but the latter only at 3 degrees C. The reactivation of photosynthesis seemed to involve photosystem II over photosystem I, as 7 d of photoperiod after the prolonged darkness was not enough to fully recover the PAM-related photosynthetic parameters. Only small changes were recorded in the internal chemical composition (total C, total N, carbohydrates, proteins, and lipids), but species-specific differences were observed. Unlike subarctic areas with an operating photoperiod along the year, a warmer polar night might pose a limit to the ability of multi-year seaweeds to occupy the new ice-free illuminated areas of the Arctic coasts, so that newcomers will potentially be restricted to the spring-summer season.

Automated summary

This study simulated continuous winter darkness at a latitude of 79 degrees N and investigated the effects on four species of Arctic seaweeds. The results showed that high temperature enhanced biomass loss during darkness, and the two laminarians were unable to resume growth upon re-illumination. All species maintained photosynthetic ability during the whole dark period. The reactivation of photosynthesis seemed to involve photosystem II. This study suggests that a warmer polar night might pose a limit to the ability of multi-year seaweeds to occupy new ice-free areas.