MEPS 657:43-57 (2021)  -  DOI: https://doi.org/10.3354/meps13532

ABSTRACT: Polar regions are facing rapid temperature increase. In Arctic fjord systems, increased temperatures result in hyposalinity caused by the melting of sea ice and glaciers and freshwater run-off. Additionally, enhanced freshwater discharge and intrusion of nutrient-rich Atlantic water may result in nutrient input in summer. Combined, these factors might have a strong impact on primary producers, such as the abundant kelp species Saccharina latissima, an important foundation species in Arctic shallow-water coastal ecosystems. We ran 2 short-term 2factor experiments with field samples from Kongsfjorden (Svalbard) to evaluate the impact of temperature increase in summer combined with hyposalinity (temperature × salinity) or nutrient enrichment (temperature × nutrients) on the physiological and biochemical status of Arctic S. latissima. In the temperature × salinity experiment, growth and maximum photosynthetic quantum yield of photosystem II (F_v/F_m) were generally not affected. Temperature increase resulted in increased C:N ratios, based on decreasing nitrogen assimilation. Overall, hyposalinity had no severe effect but resulted in lower phlorotannin concentrations. Growth and F_v/F_m improved with increasing temperatures and nutrient enrichment. The de-epoxidation state of the xanthophyll cycle and mannitol declined at higher temperatures. Regarding other biochemical response variables, nutrients had no major impact (temperature × nutrients). In conclusion, in line with its broad latitudinal distribution range and adaptability, S. latissima proved to be highly resilient to changing abiotic drivers and will likely be promoted by warming in the future Arctic.

KEY WORDS: Kelp · Interactive effects · Temperature · Nutrients · Salinity · C:N ratio · Mannitol · Pigments