Biocrusts from Iceland and Svalbard: Does microbial community composition differ substantially?

A wide range of microorganisms inhabit biocrusts of arctic and sub-arctic regions. These taxa live and thrive under extreme conditions and, moreover, play important roles in biogeochemical cycling. Nevertheless, their diversity and abundance remain ambiguous. Here, we studied microbial community composition in biocrusts from Svalbard and Iceland using amplicon sequencing and epifluorescence microscopy. Sequencing of 16S rRNA gene revealed the dominance of Chloroflexi in the biocrusts from Iceland and Longyearbyen, and Acidobacteria in the biocrusts from Ny-Ålesund and South Svalbard. Within the 18S rRNA gene sequencing dataset, Chloroplastida prevailed in all the samples with dominance of Trebouxiophyceae in the biocrusts from Ny-Ålesund and Embryophyta in the biocrusts from the other localities. Furthermore, cyanobacterial number of cells and biovolume exceeded the microalgal in the biocrusts. Community compositions in the studied sites were correlated to the measured chemical parameters such as conductivity, pH, soil organic matter and mineral nitrogen contents. In addition, co-occurrence analysis showed the dominance of positive potential interactions and, bacterial and eukaryotic taxa co-occurred more frequently together

The sugar kelp Saccharina latissima II: Recent advances in farming and application

The sugar kelp Saccharina latissima has received intense scientific attention over the last decades. In recent years, interest in cultivation of the species has strongly increased in the North Atlantic Ocean and the Eastern Pacific Ocean, driven by the great potential of S. latissima to be utilised for various industrial applications, including food, feed, and biomaterials. Accordingly, current research has focused on improving farming methods and technology, environmental impacts, and site selection. In addition, many studies have investigated the varying chemical composition of S. latissima, extraction of commercially interesting components, and the use of the biomass and its derived components in various applications. This review provides a comprehensive overview of farming and applications of S. latissima from the last 15 years. Additional insights on other research topics, such as ecology, physiology, biochemical and molecular biology of S. latissima, are given in the first review, “The sugar kelp Saccharina latissima I: recent advances in a changing climate” (Diehl et al. 2023).publishedVersio

The transcriptomic response of the cold-water coral Desmophyllum dianthus to experimental changes in pH

The seawater pH is influenced by the interaction of various natural physical and biological factors. Since the beginning of industrialisation, anthropogenic activities are also having a significant impact on the seawater pH, as the atmospheric increase of the carbon dioxide (CO2) concentration led to an enrichment of the ocean with CO2. The release of protons during the reaction of CO2 with water molecules results in a declining pH (ocean acidification; OA). Apart from the seawater pH, the aragonite saturation state (Ωarag) is commonly used to measure the OA, as it describes the ‘easiness to calcify’ and is therefore biologically relevant. With decreasing pH, the Ωarag is also decreasing and calcifying organisms have to invest more energy to maintain their calcium carbonate structures, most prominently in cold and deep waters. Therefore, scleractinian cold-water corals (CWCs), such as the cosmopolitan species Desmophyllum dianthus, were thought to be among the taxa most threatened by OA, as they are mainly restricted to water temperatures between 4–12 °C and water depths below 50 m. However, their reported occurrence in aragonite under-saturated waters indicates that they are able to mitigate the negative impacts of the low Ωarag. The aim of this study was to gain information on the regulations and mechanisms that allow the CWC D. dianthus to thrive under low-pH conditions. An understanding of the physiological and molecular processes affected by low-pH conditions will help to assess the development and future biogeographic distribution of D. dianthus. Therefore, corals acclimated to pH 8.0 were exposed for two weeks to low-pH conditions (pH 7.4), to assess their short-term acclimation potential to an experimental reduction of the pH conditions. Afterwards, the pH was turned to pH 8.0 for two months, to determine their recovery potential. Corals being exposed to pH 8.0 during the whole experiment served as control. Physiological and transcriptomic response parameters were measured at various sampling times throughout the experiment. The observed gene expression patterns were compared to field samples that grew under two different pH conditions (pH 7.5; pH 7.8). The results of this study suggest that D. dianthus is highly tolerant towards short-term changes in the seawater pH, in a range corresponding to the natural pH conditions. While no significant pH-dependent differences were detected on a physiological level, the dynamic regulation of the transcriptome indicates that the experimental pH-range was within the limits of phenotypic buffering. As a pH-dependent change was neither detected in the calcification rates nor in the expression of ion transporters, this suggests that the experimental changes of the seawater pH had no negative effect on calcification. However, the downregulation of genes coding for cytoskeletal elements (actin and tubulin) (Δ log2 fold change > 20) might be an indicator for a change in the crystal structure of the calcium carbonate skeleton. Further, no significant changes of the respiration rate during the two weeks of low-pH conditions could be observed, though the median respiration rate of the corals exposed to pH 7.4 was 15–38 % lower compared to the control. In combination with the immediate downregulation of genes after first reaching pH 7.4, this may be an indicator for metabolic suppression under acute low-pH stress. This is supported by the downregulation of the expression of genes belonging to the protein synthesising apparatus (histones, ribosomal subunits and elongation factor) (Δ log2 fold change > 20). A change in the feeding regime during the recovery phase showed a strong regulation on both physiological (60–85 % higher calcification-; 50–60% higher respiration rates) and transcriptomic (1195 differential regulated transcripts) level, indicating that the food availability influences the susceptibility of D. dianthus towards low-pH stress. Comparing the observed gene expression patterns of the pH exposure experiment with field samples, 38 % of all differentially expressed transcripts were found in the field samples, suggesting that the transcriptome of D. dianthus is highly variable and strongly depends on the prevailing abiotic conditions. Stress- and transcription-related genes (metalloproteinase and zinc fingers) (Δ log2 fold change = 3.5) were found upregulated in those samples growing under pH 7.5 in the field. However, as the field samples were influenced by a multitude of fluctuating environmental factors, the assignment of these genes as a pH-related response is difficult. In summary, this study demonstrated that D. dianthus has comprehensive mechanisms to withstand short-term pH fluctuations. To be able to draw conclusions about the development of D. dianthus, the observed metabolic suppression and its long-term effects on the corals fitness must be examined. In addition, the strong response towards the increased food supply must be noted, as the nutritional status may be influencing the corals sensitivity towards low-pH conditions

Lab experiment on the effects of temperature on kelp respiration rates

Kelps act as ecosystem engineers and foundation species on many polar rocky shore coastlines. The main driver for their vertical and latitudinal distribution is the underwater light climate and temperature. Both are changing drastically in the Arctic in the course of global climate change. It was the aim of this study to analyse the effects of rising temperature and deteriorating underwater light climate on the potential habitat of kelps in the Arctic. A laboratory experiment, in which we determined temperature-related changes in the light-use characteristics of two temperate kelp species (Alaria esculenta, Saccharina latissima) at 3, 7, and 11 °C. Therefore, grown sporophytes were sampled in the field from a sampling depth of 6–9 m. Meristematic discs (Ø 2 cm) were cut and distributed between temperature treatments and replicates. The experiment ran for seven days, during which the treatment temperature was increased every two days by 4 °C until treatment temperature was reached, allowing for successive acclimation. The photosynthesis vs. irradiance curves were measured with a 4-channel optode set-up (FireStingO2 Fibre-Optic Oxygen Meter FSO2-01, PyroScience Sensor technology, Aachen, Germany) by analysing the oxygen evolution in response to different light intensities within a 25 mL Schott bottle, each containing three meristematic discs. Maximum photosynthetic quantum yield was measured using a pulse amplitude modulated fluorometer (Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany). Pigment analysis was analysed with a High-Performance Liquid Chromatograph (HPLC, LaChromElite® system, L-2200 autosampler (chilled), DA-detetctor L-2450; VWR-Hitachi International GmbH, Darmstadt, Germany)

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

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, temperature induced 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

Irradiance data at different depths and sites for field sampling in the Arctic fjord Kongsfjorden

Kelps act as ecosystem engineers and foundation species on many polar rocky shore coastlines. The main driver for their vertical and latitudinal distribution is the underwater light climate and temperature. Both are changing drastically in the Arctic in the course of global climate change. It was the aim of this study to analyse the effects of rising temperature and deteriorating underwater light climate on the potential habitat of kelps in the Arctic. The analyses of the underwater light climate in Arctic Kongsfjorden, Svalbard in July 2021. We divided Kongsfjorden in three areas, which are influenced by the run-off of sea-terminating glaciers (station A–J), the run-off of a land-terminating glacier (station K–O) and mostly clear water (control, station P–Q). In each area, we measured the spectrally resolved underwater light climate in the UV-B radiation (280-320 nm), UV-A radiation (320-400 nm) and photosynthetically active radiation (PAR, 400-700 nm) with a RAMSES-ACC-UV/VIS radiometer (TriOS Optical Sensor, Oldenburg, Germany) from 0–12.5 m. UV-B, UV-A and PAR were calculated by integrating the irradiance over the respective wavelengths

Seasonal and inter-annual variability in the heatwave tolerance of the kelp Saccharina latissima

Temperature is a major driver for the geographical distribution of organisms, such as the foundation kelp species Saccharina latissima. Globally rising sea surface temperatures and intensification of marine heatwaves have already led to local loss of kelp populations. We investigated temporal variations in the thermal susceptibility of S. latissima. Therefore, we assessed the stress responses of field sporophytes sampled from Helgoland (German Bight) to an experimental heat wave scenario in June 2018, August 2018, and August 2019. The experiment in June 2018 was conducted by Diehl et al. (2021a) and the respective dataset (Diehl et al. 2021b, https://doi.org/10.1594/PANGAEA.931637) was re-evaluated for this study. Treatment temperatures (18, 20, 22, 24 °C) were based on 18 °C summer mean sea surface temperature on Helgoland as control, and Δ+2, Δ+4, Δ+6 °C as temperature-amplitude treatments, mimicking marine heatwaves. After a three-days wound healing phase, seven days of temperature acclimation (day 0-7) and seven days of temperature treatment (day 8-14) followed. The survival, growth and maximum photosynthetic quantum yield (Fv/Fm; June 2018/August 2018: ImagingPAM, Walz Imaging PAM Maxi Version M-series; August 2019: Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany) were measured on day 0 and day 14. To highlight changes as response to the experimental heat wave, physiological parameters were shown as percentage of the initial values. Absolute concentrations of pigments were analyzed using a HPLC. Afterwards, accessory pigment (Acc) and xanthophyll cycle pigment (VAZ) concentration, as well as the de-epoxidation state of the xanthophyll cycle (DPS) and ratios were calculated

Seasonal and inter‐annual variability in the heatwave tolerance of the kelp Saccharina latissima (Laminariales, Phaeophyceae)

The geographical distribution of organisms, such as the foun- dation kelp species Saccharina 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 of S. latissima by assessing stress responses of field sporophytes sampled from Helgoland (Ger- man 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 compo- sition. Survival decreased with increasing environmental and experimental temperatures. Growth revealed seasonal pat- terns, being higher in June than in August, whereas Fv/Fm decreased 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 tol- erance of S. latissima towards heatwaves in summer is signifi- cantly affected by the environmental history it previously experienced