• Energy Research

The Arctic is seasonally exposed to long periods of low temperatures and complete darkness. Consequently, perennial primary producers have to apply strategies to maximize energy efficiency. Global warming is occurring in the Arctic faster than the rest of the globe. The highest amplitude of temperature rise occurs during Polar Night. To determine the stress resistance of the ecosystem-engineering kelp Laminaria digitata against Arctic winter warming, non-meristematic discs of adult sporophytes from Porsangerfjorden (Finnmark, Norway) were kept in total darkness at 0°C and 5°C over a period of three months. Physiological variables, namely maximum quantum yield of photosynthesis (Fv/Fm) and dry weight, as well as underlying biochemical variables including pigments, storage carbohydrates, total carbon and total nitrogen were monitored throughout the experiment. Although all samples remained in generally good condition with Fv/Fm values above 0.6, L. digitata performed better at 0°C than at 5°C. Depletion of metabolic products resulted in a constant decrease of dry weight over time. A strong decrease in mannitol and laminarin was observed, with greater reductions at 5°C than at 0°C. However, the total carbon content did not change, indicating that the sporophytes were not suffering from “starvation stress” during the long period of darkness. A decline was also observed in the accessory pigments and the pool of xanthophyll cycle pigments, particularly at 5°C. Our results indicate that L. digitata has a more active metabolism, but a lower physiological and biochemical performance at higher temperatures in the Arctic winter. Obviously, L. digitata is well adapted to Arctic Polar Night conditions, regardless of having its distributional center at lower latitudes. Despite a reduced vitality at higher temperatures, a serious decline in Arctic populations of L. digitata due to winter warming is not expected for the near future.

AbstractDue to global rises in temperature, recent studies predict marine species shifting toward higher latitudes. We investigated the impact of interacting abiotic drivers on the distribution potential of the temperate kelpLaminaria hyperborea. The ecosystem engineering species is widespread along European coasts but has not yet been observed in the High Arctic, although it can survive several months of low temperatures and darkness. To investigate its ability to extend northward in future, we conducted a long‐term multifactorial experiment with sporophytes from Porsangerfjorden, Norway—close to the species' documented northernmost distribution margin. The samples were exposed to three different photoperiods (PolarDay, LongDay, and PolarNight) at 0°C, 5°C, and 10°C for 3 months. Optimum quantum yield of photosynthesis (Fv/Fm), dry weight, pigments, phlorotannins, and storage carbohydrates were monitored. Both physiological and biochemical parameters revealed thatL. hyperboreawas strongly influenced by the different photoperiods and their interaction with temperature, while temperature alone exerted only minor effects. TheFv/Fmdata were integrated into a species distribution model to project a possible northward expansion ofL. hyperborea. The combination of extended day lengths and low temperatures appeared to be the limiting reason for northward spread ofL. hyperboreauntil recently. However, with water temperatures reaching 10°C in summer, this kelp will be able to thrive also in the High Arctic. Moreover, no evidence of stress to Arctic winter warming was observed. Consequently,L. hyperboreahas a high potential for spreading northward with further warming which may significantly affect the structure and function of Arctic ecosystems.

The Arctic region is currently facing substantial environmental changes due to global warming. Melting glaciers cause reduced salinity environments in coastal Arctic habitats, which may be stressful for kelp beds. To investigate the responses of the kelp Saccharina latissima to the warming Arctic, we studied the transcriptomic changes of S. latissima from Kongsfjorden (Svalbard, Norway) over a 24‐hour exposure to two salinities (Absolute Salinity [SA] 20 and 30) after a 7‐day pre‐acclimation at three temperatures (0, 8 and 15°C). In addition, corresponding physiological data were assessed during an 11‐days salinity/temperature experiment. Growth and maximal quantum yield for photosystem II fluorescence were positively affected by increased temperature during acclimation, whereas hyposalinity caused negative effects at the last day of treatment. In contrast, hyposalinity induced marked changes on the transcriptomic level. Compared to the control (8°C – SA 30), the 8°C – SA 20 exhibited the highest number of differentially expressed genes (DEGs), followed by the 0°C – SA 20. Comparisons indicate that S. latissima tends to convert its energy from primary metabolism (e.g. photosynthesis) to antioxidant activity under hyposaline stress. The increase in physiological performance at 15°C shows that S. latissima in the Arctic region can adjust and might even benefit from increased temperatures. However, in Arctic fjord environments its performance might become impaired by decreased salinity as a result of ice melting.

SummaryThe geographical distribution of organisms, such as the foundation kelp speciesSaccharina latissima, is mainly driven by temperature. Globally increasing sea surface temperature and further intensification of marine heatwaves have already resulted in local extinction of kelp populations worldwide. In the present study, we investigated temporal variation in the thermal susceptibility ofS. latissimaby assessing stress responses of field sporophytes sampled from Helgoland (German Bight) in June 2018, August 2018 and August 2019 in heatwave scenarios. We analyzed survival, growth, maximum quantum yield of photosystem II (Fv/Fm) and pigment composition. Survival decreased with increasing environmental and experimental temperatures. Growth revealed seasonal patterns, being higher in June than in August, whereasFv/Fmdecreased with increasing temperature, independent of the sampling time. We found an increase in the concentration of light harvesting pigments and in the de‐epoxidation state of the xanthophyll cycle with higher treatment temperature. This pattern was even more pronounced at higher environmental temperature prior to the experiment (June 2018 < August 2019 < August 2018). Our results show that the thermal tolerance ofS. latissimatowards heatwaves in summer is significantly affected by the environmental history it previously experienced.

A survey of age class distribution and density of kelps was performed at Hansneset, Blomstrand in Kongsfjorden, Svalbard, at depths of 2.5, 5 and 10m in June - August 2021. This dataset is part of a time series and complements the investigations conducted in 2013 (Bartsch et al., 2016; doi:doi:10.1007/s00300-015-1870-1). The goal was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period alterations in kelp demography were observed.The data contains counts of individual kelps by depth, quadrat (replicate), species, and age class. Kelps younger than 1 year are classed as 'Juveniles', rather than '0years'. The 'Total_Individuals' value is the sum of all kelps of the same species, at the same depth and within the same quadrat (replicate). Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible here. Historically these kelps were considered Laminaria digitata, whereas here they have been classified simply as Laminariales.

Surveys of C:N ratios, carbon and nitrogen content in the blades of adult kelps at Hansneset, Blomstrand in Kongsfjorden, Svalbard, were performed along a depth transect down to 10m in June - August 2021. As major coastal foundation species, kelps contribute substantially to the coastal carbon cycle. The kelp forest at the sampling site changed substantially over the last 25 years and serves as a case study to document changes in Arctic kelp forest dynamics in an Arctic fjord system influenced by Arctic warming and glacial melt. The study showed that carbon and nitrogen allocation strategies significantly vary between the three prevailing kelps: A. esculenta, S. latissima, and 'Digitate Kelps' (i.e. the visually similar Laminaria digitata and Hedophyllum nigripes). Species dominance relationships in the kelp forest changed over time, which implies consequences for the coastal carbon budget and biological carbon sequestration in the fjord system. The data contains the percent of Nitrogen (N [%]), Carbon ([%]), and the ratio between the two (C:N [ratio]) found within the blades of kelps by depth, quadrat (replicate), and species. Up to five individuals were taken from each quadrat when possible. Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible here. Historically these kelps were considered Laminaria digitata.

Surveys were performed of abundance and lower depth distribution of biomass dominant brown algae species at Hansneset, Blomstrand in Kongsfjorden, Svalbard, between 2 m and 20 m depth in June - August 2021. This dataset is part of a time series currently spanning over 25 years and complements the studies conducted in 1996/98 (Hop et al., 2012, doi:10.1515/bot-2012-0097) and 2012-14 (Bartsch et al., 2016, doi:10.1007/s00300-015-1870-1). The aim was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period alterations were observed in the seaweed community, especially kelps as major coastal foundation species.The depth distribution of biomass dominant brown algae was semi-quantitatively (visually) investigated by scientific divers in five parallel transects off the coastline covering the vertical gradient between 2 m and 20 m depth. For each replicate a 1x1 m quadrat divided into four 50 x 50 cm subquadrats was placed on the ground or above the kelps at every depth meter along the transect and species occurrence was documented as attached frequency within each subquadrat. This resulted in a relative frequency of 0 - 4 per replicate (Frequency count). Additionally, the visual presence of the species in the close surroundings of each replicate was documented 0 or 1 (Additional Presence). In summary this generates in a maximum presence score of 5 for each species per replicate. The target replication was five per depth but due to depth corrections to chart datum this resulted in n = 3–8 for each depth and species. The presence (1) or absence (0) of rocks, pebbles, and/or sand was all documented.

Global warming affects the Arctic much faster than the rest of the globe, with the highest amplitude of temperature rise occurring during the Polar Night. To determine the stress resistance of the ecosystem-engineering kelp Laminaria digitata against Arctic winter warming, non-meristematic discs of adult sporophytes from Porsangerfjorden (Finnmark, Norway) were kept in total darkness at 0°C and 5°C over a period of three months. The maximum photosynthetic quantum yield of photosystem II (Fv/Fm; Imaging-PAM, Walz GmbH Mess- und Regeltechnik, Effeltrich, Germany) was monitored once a week. For monitoring of potential growth, the size (area) of the algal discs was photographed every two weeks and analyzed with ImageJ (Version 1.52a). Every four weeks, subsamples for monitoring the dry weight and for the biochemical analyses were taken. Laminarin content was determined following via enzymatic digestion. C:N ratio was analyzed with an Elementar Analyzer. Mannitol concentration was analyzed using a HPLC. Absolut pigment concentrations were also analyzed using a HPLC and pool sizes, the de-epoxidation state of the xanthophyll cycle (DPS), and the ratios calculated afterwards. Treatment details ----------------------------Laminaria digitata samples from the Porsangerfjorden, Finnmark, Norway0°C and 5°C, total darkness for 3 monthsw0 = week 0 (start)w4 = week 4w8 = week 8w12 = week 12 (end)set-up:2-L aerated Kautex bottles, 1/40 PES, medium changed 2x/weekSample: These values are used to differentiate multiple similar samples within the same replicate. They do not denote a relationship between weeks. E.g. Sample #3 from week 0 (w0) of Replicate 2, is not necessarily a sample of the same organism for Sample #3 from week 1 (w1) of Replicate 2. Meaning that Samples should not be taken as time series of measures of the same organism through time.