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Laminaria digitata gametophyte survival and sporophyte formation during exposure to increased temperatures

To assess the thermal adaptation of microscopic stages of the kelp Laminaria digitata along latitudes, we conducted laboratory experiments on samples from six locations in the NE Atlantic (Spitsbergen (SPT), Tromsø (TRM), Bodø (BOD; all Norway), Helgoland (HLG; Germany), Roscoff (ROS) and Quiberon (QUI; both France)), spanning the species' entire distribution range. Gametophyte stock cultures from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research were used. Prior to the experiments, cultures were stored at 15°C in iron-free ½ Provasoli enriched seawater in 3-4 µmol photons/m²/s red light. In experiment 1, we exposed gametophytes to (sub-) lethal high priming temperatures (20-25°C) for two weeks, followed by two weeks of recovery at 15°C, to observe gametophyte survival and sporophyte formation. During the experiments, samples were kept in 15 µmol photons/m²/s white light under a 16:8h light:dark cycle.

Bottle incubations of a North Sea phytoplankton community exposed to acute vs. gradual temperature increases and different timings of nutrient addition across various nitrogen:phosphorus ratios

To determine the effect of the rate of temperature increase (acute vs. gradual) and magnitude as well as the timing of nutrient addition on a natural marine phytoplankton community, a bottle incubation experiment has been conducted at the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany. The community was collected at the Helgoland Roads long-term time series site in the German part of the North Sea (https://deims.org/1e96ef9b-0915-4661-849f-b3a72f5aa9b1) on the 6ᵗʰ of March 2022. The surface water containing the phytoplankton community was collected from the RV HEINCKE with a pipe covered with a 200 µm net attached to a diaphragm pump. In the first experimental run, the community was exposed to either gradual or acute temperature increase (from 6 to either 12 or 18°C) with 25 different N:P supply ratios added as a batch at the beginning of the bottle incubation. Simultaneously, the same community was gradually acclimated to their experimental temperatures under ambient nutrients and was used in a second experimental run in which it received the same 25 different N:P supply ratios after temperature acclimation. The light conditions were set to 175 µmol s-1 m-2 and a day-night cycle of 12h:12h which corresponds to the natural conditions at that time of the year. With this, it was possible to test the effect of a gradual vs. acute temperature increase and the timing of nutrient addition i.e., before or after the temperature change. This experimental set-up summed up to 400 units (8 temperature treatments x 5 nitrogen levels x 5 phosphorus levels x 2 replicates). Each experimental run was ended after 12 days. Fluorescence (395/680 Exc./Em.) was measured every second day using a SYNERGY H1 microplate reader (BioTek®) to determine phototrophic growth over time. At the end of each experiment, one replicate was filtered onto pre-combusted acid-washed glass microfiber filters (WHATMAN® GF/C) for intracellular carbon (POC), nitrogen (PON), and phosphorus (POP) content. The POP filters were pre-combusted and then analysed by molybdate reaction after digestion with a potassium peroxydisulfate solution (Wetzel and Likens 2003). The POC and PON filters were dried at 60°C before they were measured in an elemental analyser (Flash EA 1112, Thermo Scientific, Walthman, MA, USA).

Laminaria digitata gametophyte survival and microscopic sporophyte formation, abundance and growth during exposure to decreased temperatures

To assess the thermal adaptation of microscopic stages of the kelp Laminaria digitata along latitudes, we conducted laboratory experiments on samples from six locations in the NE Atlantic (Spitsbergen (SPT), Tromsø (TRM), Bodø (BOD; all Norway), Helgoland (HLG; Germany), Roscoff (ROS) and Quiberon (QUI; both France)), spanning the species' entire distribution range. Gametophyte stock cultures from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research were used. Prior to the experiments, cultures were stored at 15°C in iron-free ½ Provasoli enriched seawater in 3-4 µmol photons/m²/s red light. In experiment 2, samples were subjected to (sub-) optimal low temperatures (0-15°C) for 21 days, to assess gametophyte survival, sporophyte formation and growth. During the experiments, samples were kept in 15 µmol photons/m²/s white light under a 16:8h light:dark cycle. Sporophyte growth rates both in length and in width were determined as follows: GR = (x2-x1)/(t2-t1), where x is the length or width (μm) and t is the time in weeks at time point 1 and 2.

Integrated survival of Laminaria digitata gametophytes exposed to increased temperatures

To assess the thermal adaptation of microscopic stages of the kelp Laminaria digitata along latitudes, we conducted laboratory experiments on samples from six locations in the NE Atlantic (Spitsbergen (SPT), Tromsø (TRM), Bodø (BOD; all Norway), Helgoland (HLG; Germany), Roscoff (ROS) and Quiberon (QUI; both France)), spanning the species' entire distribution range. Gametophyte stock cultures from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research were used. Prior to the experiments, cultures were stored at 15°C in iron-free ½ Provasoli enriched seawater in 3-4 µmol photons/m²/s red light. In experiment 1, we exposed gametophytes to (sub-) lethal high priming temperatures (20-25°C) for two weeks, followed by two weeks of recovery at 15°C, to observe gametophyte survival and sporophyte formation. During the experiments, samples were kept in 15 µmol photons/m²/s white light under a 16:8h light:dark cycle.

Local adaptation of microscopic stages of North Atlantic Laminaria digitata to high and low temperatures along latitudes: survival, reproduction and growth

To assess the thermal adaptation of microscopic stages of the kelp Laminaria digitata along latitudes, we conducted laboratory experiments on samples from six locations in the NE Atlantic (Spitsbergen (SPT), Tromsø (TRM), Bodø (BOD; all Norway), Helgoland (HLG; Germany), Roscoff (ROS) and Quiberon (QUI; both France)), spanning the species' entire distribution range. In experiment 1, we exposed gametophytes to (sub-) lethal high priming temperatures (20-25°C) for two weeks, followed by two weeks of recovery at 15°C, to observe gametophyte survival and sporophyte formation. In experiment 2, samples were subjected to (sub-) optimal low temperatures (0-15°C) for 21 days, to assess gametophyte survival, sporophyte formation and growth. During the experiments, samples were kept in 15 µmol photons/m²/s white light under a 16:8h light:dark cycle. Prior to the experiments, cultures were stored at 15°C in iron-free ½ Provasoli enriched seawater in 3-4 µmol photons/m²/s red light.

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.

Mussel (Mytilus) growth and metabolic performance data from long (five-week) and short-term (one-day) thermal fluctuation experiments conducted in 2018

These data were produced in two experimental studies. The first experiment was conducted on September 22, 2018. Over a five-week period, mussel shell-length (mm d-1), mass, and tissue dry weight growth (both mg d-1) were assessed in response to twelve temperature scenarios composed of constant versus daily fluctuating regimes using Kiel Indoor Benthocosms (KIBs). In the second experiment, started on November 20, 2018, filtration (feeding) and respiration rates of different mussel individuals were recorded in seven temporally repeated trials of one-day thermal fluctuations using the Fluorometer and Oximeter-equipped Flow-through Setup (FOFS; Vajedsamiei et al., 2021).

Heat resilience of intraspecific outbred compared to inbred lineages in the kelp Laminaria digitata: gametogenesis, thermal tolerance and growth

In a mechanistic investigation of heat stress, heterosis (hybrid vigour), and underlying gene expression patterns, we assessed the thermal performance of inbred (selfings) and outbred (reciprocal crosses) sporophytes of the N-Atlantic kelp Laminaria digitata among clonal isolates from two divergent populations; one from the temperate North Sea (Helgoland) and one from the Arctic (Spitsbergen). First, we investigated the upper thermal tolerance of microscopic sporophytes in a 14-day experiment applying sublethal to lethal 20–23°C. We then subjected 4–7 cm long sporophytes to a control temperature (10°C), moderate (19°C) and sublethal to lethal heat stress (20.5°C) for 18 days to assess the physiological parameters growth and optimum quantum yield.

Summer heatwave impacts on the European kelp Saccharina latissima across its latitudinal distribution gradient – raw data to temperature-amplitude experiment with field material from five different locations

Temperature is a major factor for the global biogeographic pattern of marine benthic algal species and their loss has serious consequences for ecosystems. Local adaptation and phenotypic plasticity of species can result in intraspecific differences of thermal tolerance, and population loss might not only occur at thermal trailing edges. Understanding the underlying physiological and biochemical response mechanisms is from major importance. Therefore, we run the same short-term experiment with field sporophytes of Saccharina latissima from five locations along the European coast (Spitsbergen, Bodø, Bergen, Helgoland, Locmariaquer). We increased each respective mean summer temperature (control, ±0°C) by +2, +4 and +6°C to mimic realistic local heatwave events. The maximum photosynthetic quantum yield of photosystem II (Fv/Fm; Imaging-PAM, Walz GmbH Mess- und Regeltechnik, Effeltrich, Germany) was monitored every day. For growth, the size of the algal discs was photographed every second day, analyzed with ImageJ (Version 1.52a). Absolute concentrations of all pigments were analyzed using a HPLC. Afterwards, the pool sizes, the de-epoxidation state of the xanthophyll cycle (DPS), and the ratios were calculated. The C:N ratio, total nitrogen and total carbon content were analyzed with an elemental analyzer. Mannitol concentration was also analyzed in a HPLC. Phlorotannins were analyzed using the photometric Folin-Ciocalteu method.

Heatwave experiment in Kiel Outdoor Benthocosms, 2015: dataset for Fucus vesiculosus and Zostera marina response variables

13 response variable have been measured for Fucus vesiculosus and Zostera marina. Year: 2015 Where: Kiel Outdoor Benthocosm Treatments: - Co (0HW) = ambient treatment with no heatwaves - 1HW = one summer heatwave - 3HWs = three heatwaves, 2 spring/early summer heatwaves After 3HW means end of the experiment.

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