Glacial retreat and rising temperatures are limiting the expansion of temperate kelp species in the future Arctic

Abstract

Kelps act as ecosystem engineers on many polar rocky shore coastlines. The underwater light climate and temperature are the main drivers for their vertical and latitudinal distribution. With temperatures rising globally, an Arctic expansion of temperate kelp species and an accelerating glacial melt is predicted. It was our aim to investigate the effects of retreating glaciers and rising temperatures on the potential habitat of kelps in Arctic fjords. We analyzed the underwater light climate of areas being influenced by different stages of glacial retreat (sea-terminating glacier, land-terminating glacier, coastal water) in Arctic Kongsfjorden. We observed reduced light intensities and a changed spectral composition in glacial meltwater plumes, potentially resulting in an upward shift of the lower depth limit of kelp, counteracting the predicted biomass increase in the Arctic. Furthermore, we studied temperature-related changes in light-use characteristics in two kelp species (Alaria esculenta, Saccharina latissima) at 3 C, 7 C, and 11 C. Rising temperatures lead to a significant increase of the compensation irradiance of A. esculenta. The dark respiration of S. latissima increased significantly, correlating with a decreasing carbon content. We detected no differences in photosynthetic rates, although the chlorophyll a concentration of A. esculenta was $ 78% higher compared to S. latissima. Ultimately, temperatureinduced changes in kelps light-use characteristics might lead to a changed species composition, as we found A. esculenta better adapted to polar conditions. We conclude that the deterioration of the underwater light climate and the temperature increase may drive substantial changes of the future Arctic kelp forest structure.

Arctic kelp forest decline -- a consequence of melting glaciers?

“…This elongation of the open water period leads to an extension of the vegetation period which theoretically promotes kelp forest depth extension as long as it is accompanied by improved water transparency (Castro de la Guardia et al, 2023). However, our results indicate that this potentially positive effect of less ice scouring and reduced sea ice cover for kelp communities gets overshadowed by the counteracting effects of sediment plumes occurring as a consequence of increasing glacial melt (Niedzwiedz & Bischof, 2023;Payne & Roesler, 2019). Geyman et al (2022) showed that glaciers on Svalbard (including Kongsfjorden area), retreated substantially over time as a response to warming summer temperatures.…”

“…Kongsfjorden is lined by several glaciers at different stages of glacial retreat with four main calving tidewater glaciers and several land-terminating glaciers including Brøggerbreen at the Bayelva river (Pavlov et al, 2019;Svendsen et al, 2002). When freshwater from glacial melt, snow and precipitation enters the fjord in summer, it carries suspended terrestrial particles that form large sediment plumes which alter the spectral composition of the underwater light regime available for macroalgal photosynthesis (Niedzwiedz & Bischof, 2023;Pavlov et al, 2019).…”

“…These changes in the kelp forest community structure were discussed as being likely a consequence of altering abiotic conditions caused by Arctic warming and hence may largely impact coastal ecosystem services (Filbee-Dexter et al, 2019;Bartsch et al, 2016). Furthermore, the responses of different species and life stages of kelps in multi-stressor experiments indicate that some kelp species may benefit from climate change while others will retreat (Niedzwiedz & Bischof, 2023;Diehl & Bischof, 2021;Franke et al, 2021;Roleda, 2016;Zacher et al, 2016).…”

Photophysiologically active green, red, and brown macroalgae living in the Arctic Polar Night

“…Increasing temperatures, sedimentation rates and decreasing sea ice cover over the past decade in Kongsfjorden, Svalbard, have altered the underwater light climate, such as darkening of the fjord in summer 23 , 24 and resulted in changes in the vertical distributions of algae species 2 , 18 . This highlights the need for more studies on health state, and seasonality of macroalgae.…”

Underwater light environment in Arctic fjords

“…However, it is still very uncertain to what extent, and for how long, PAR will continue to change in Arctic fjords (Walch et al, 2022). Dissolved organic matter, which affects PAR availability, may also be altering benthic ecology (Sejr et al, 2022) or otherwise negatively affecting macroalgae communities (Niedzwiedz & Bischof, 2023). Understanding these changes is important and timely, as shallow Arctic fjord communities are predicted to shift from invertebratedominated to algal-dominated communities (Kortsch et al, 2012;Lebrun et al, 2022).…”