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We examined the effect of gametophyte priming on early life stages of Saccharina latissima (gametophyte growth, sporophyte recruitment, juvenile sporophyte growth) and adult sporophytes harvested after growing for six months in mariculture (size and biomass, biochemical composition) in two experiments. Experiment 1: we primed S. latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks, during which we assessed relative gametophyte growth rates (from day 0 – 5), progression of gametogenesis, and sporophyte recruitment. Resulting sporophytes reared at 10°C were subjected to a 14-day temperature gradient treatment spanning 7 temperatures (0, 5, 10, 15, 20, 21.5, 23°C). We measured sporophyte growth (length and relative growth rates) after 7 and 14 days. Experiment 2: primed (0°C, 10°C, 20°C; 3 weeks) gametophytes (Lofoten 2023; 10°C mixed culture; n = 5) were sown on ropes and reared in a mariculture experiment (2 months hatchery, 4 months mariculture). Adult sporophytes were sampled and we measured growth (sporophyte length and width), total biomass (in fresh weight per m rope) and biochemical composition (C, N, mannitol, laminarin, and mineral composition). During the mariculture experiment, seawater temperature and nutrient composition was recorded at different time points. The mariculture field experiment took place at the hatchery of Polaralge AS (Sandhornøy, Norway; December - February 2024) and the deployment site of Lofoten Blue Harvest (Lilje Engla, Lofoten, Norway; 68°16'02.8N 15°06'14.8E; February – June 2024). The laboratory experiments of experiment 1 and the CN-analysis were carried out at the Alfred Wegener Institute in Bremerhaven, Germany; the mannitol analysis at the University of Rostock, Germany; the laminarin analysis at the MPI Bremen, Germany; and the mineral analysis at NIBIO Bodø, Norway.
We examined the effect of gametophyte priming on early life stages of Saccharina latissima (juvenile sporophyte growth) in a laboratory experiment: we primed S. latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks. Resulting sporophytes reared at 10°C were subjected to a 14-day temperature gradient treatment spanning 7 temperatures (0, 5, 10, 15, 20, 21.5, 23°C). We measured sporophyte growth (length and relative growth rates) after 7 and 14 days. The laboratory Experiment was carried out at the Alfred Wegener Institute in Bremerhaven, Germany.
We examined the effect of gametophyte priming on early life stages of Saccharina latissima (gametophyte growth and sporophyte recruitment) in a laboratory experiment: We primed S. latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks, during which we assessed relative gametophyte growth rates (from day 0 – 5), progression of gametogenesis, and sporophyte recruitment. The laboratory experimentwas carried out at the Alfred Wegener Institute in Bremerhaven, Germany.
We assessed the heat tolerance of microscopic, juvenile and adult sporophytes under heat stress and in response to gametophyte or sporophyte priming in five experiments. Experiment 1: we primed Saccharina latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks. Resulting microscopic sporophytes were subjected to a 14-day heat stress treatment at 20°C, 21.5°C, and 23°C, where we counted the number of alive and dead sporophytes and calculated the survival rates. Experiment 2: sporophytes were cultivated after gametogenesis for an additional 4 weeks before we subjected them to a 14-day simulated heat wave (13°C for 3 days, 16°C for 2 days, 18°C for 2 days, 20°C, 21°C and 22°C for 1 day each, 23°C and 24°C for 4 days each, and recovery at 20°C for 7 days), during which we assessed the photosynthetic performance by measuring quantum yield (Fv/Fm). Sporophytes that survived the heat wave were cultivated at 15°C for 64 days to recover, after which we measured their size (length and blade area). Experiment 3: primed (0°C, 10°C, 20°C; 3 weeks) gametophytes (Lofoten 2023; 10°C mixed culture; n = 5) were sown on ropes and reared in a mariculture experiment (2 months hatchery, 4 months mariculture). Adult sporophytes were sampled and exposed to the same 14-day heat stress treatment at 20°C, 21.5°C, 23°C with a 10°C control group. We measured growth (length and blade area), Fv/Fm, and the percentage of healthy area (as % blade area with Fv/Fm > 0.6). Experiment 4: sporophytes from the 0°C gametophyte priming treatment of the same mariculture experiment recovered at 10°C for 24 days. Meristematic discs were exposed to a 1-day sporophyte priming trigger (T). A control group (C) remained at 10°C. After 3 days recovery at 10°C both groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured growth (disc area) and Fv/Fm. Experiment 5: gametogenesis of gametophytes (Spitsbergen 2011, 2015; 5°C clonal culture, n = 5) was induced at 5°C and sporophytes reared for 6 months. Sporophytes were distributed to three treatment groups. A 17-day heat wave (from 5°C to 20°C and back) followed by a 1-day priming trigger at 21.5°C (HWT); 17 days at 10°C and a 1-day priming trigger (T); a control remaining at 10°C throughout (C). All groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured Fv/Fm, percentage of healthy area and survival. All laboratory experiments were carried out at the Alfred Wegener Institute in Bremerhaven, from January to July 2024. The mariculture experiment took place at the hatchery of Polaralge AS (Sandhornøy, Norway; December - February 2024) and the deployment site of Lofoten Blue Harvest (Lilje Engla, Lofoten, Norway; 68°16'02.8N 15°06'14.8E; February – June 2024).
We assessed the heat tolerance of microscopic, juvenile and adult sporophytes under heat stress and in response to gametophyte or sporophyte priming in five experiments. Experiment 1: we primed Saccharina latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks. Resulting microscopic sporophytes were subjected to a 14-day heat stress treatment at 20°C, 21.5°C, and 23°C, where we counted the number of alive and dead sporophytes and calculated the survival rates. Experiment 2: sporophytes were cultivated after gametogenesis for an additional 4 weeks before we subjected them to a 14-day simulated heat wave (13°C for 3 days, 16°C for 2 days, 18°C for 2 days, 20°C, 21°C and 22°C for 1 day each, 23°C and 24°C for 4 days each, and recovery at 20°C for 7 days), during which we assessed the photosynthetic performance by measuring quantum yield (Fv/Fm). Sporophytes that survived the heat wave were cultivated at 15°C for 64 days to recover, after which we measured their size (length and blade area). Experiment 3: primed (0°C, 10°C, 20°C; 3 weeks) gametophytes (Lofoten 2023; 10°C mixed culture; n = 5) were sown on ropes and reared in a mariculture experiment (2 months hatchery, 4 months mariculture). Adult sporophytes were sampled and exposed to the same 14-day heat stress treatment at 20°C, 21.5°C, 23°C with a 10°C control group. We measured growth (length and blade area), Fv/Fm, and the percentage of healthy area (as % blade area with Fv/Fm > 0.6). Experiment 4: sporophytes from the 0°C gametophyte priming treatment of the same mariculture experiment recovered at 10°C for 24 days. Meristematic discs were exposed to a 1-day sporophyte priming trigger (T). A control group (C) remained at 10°C. After 3 days recovery at 10°C both groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured growth (disc area) and Fv/Fm. Experiment 5: gametogenesis of gametophytes (Spitsbergen 2011, 2015; 5°C clonal culture, n = 5) was induced at 5°C and sporophytes reared for 6 months. Sporophytes were distributed to three treatment groups. A 17-day heat wave (from 5°C to 20°C and back) followed by a 1-day priming trigger at 21.5°C (HWT); 17 days at 10°C and a 1-day priming trigger (T); a control remaining at 10°C throughout (C). All groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured Fv/Fm, percentage of healthy area and survival. All laboratory experiments were carried out at the Alfred Wegener Institute in Bremerhaven, from January to July 2024. The mariculture experiment took place at the hatchery of Polaralge AS (Sandhornøy, Norway; December - February 2024) and the deployment site of Lofoten Blue Harvest (Lilje Engla, Lofoten, Norway; 68°16'02.8N 15°06'14.8E; February – June 2024).
We assessed the heat tolerance of microscopic, juvenile and adult sporophytes under heat stress and in response to gametophyte or sporophyte priming in five experiments. Experiment 1: we primed Saccharina latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks. Resulting microscopic sporophytes were subjected to a 14-day heat stress treatment at 20°C, 21.5°C, and 23°C, where we counted the number of alive and dead sporophytes and calculated the survival rates. Experiment 2: sporophytes were cultivated after gametogenesis for an additional 4 weeks before we subjected them to a 14-day simulated heat wave (13°C for 3 days, 16°C for 2 days, 18°C for 2 days, 20°C, 21°C and 22°C for 1 day each, 23°C and 24°C for 4 days each, and recovery at 20°C for 7 days), during which we assessed the photosynthetic performance by measuring quantum yield (Fv/Fm). Sporophytes that survived the heat wave were cultivated at 15°C for 64 days to recover, after which we measured their size (length and blade area). Experiment 3: primed (0°C, 10°C, 20°C; 3 weeks) gametophytes (Lofoten 2023; 10°C mixed culture; n = 5) were sown on ropes and reared in a mariculture experiment (2 months hatchery, 4 months mariculture). Adult sporophytes were sampled and exposed to the same 14-day heat stress treatment at 20°C, 21.5°C, 23°C with a 10°C control group. We measured growth (length and blade area), Fv/Fm, and the percentage of healthy area (as % blade area with Fv/Fm > 0.6). Experiment 4: sporophytes from the 0°C gametophyte priming treatment of the same mariculture experiment recovered at 10°C for 24 days. Meristematic discs were exposed to a 1-day sporophyte priming trigger (T). A control group (C) remained at 10°C. After 3 days recovery at 10°C both groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured growth (disc area) and Fv/Fm. Experiment 5: gametogenesis of gametophytes (Spitsbergen 2011, 2015; 5°C clonal culture, n = 5) was induced at 5°C and sporophytes reared for 6 months. Sporophytes were distributed to three treatment groups. A 17-day heat wave (from 5°C to 20°C and back) followed by a 1-day priming trigger at 21.5°C (HWT); 17 days at 10°C and a 1-day priming trigger (T); a control remaining at 10°C throughout (C). All groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured Fv/Fm, percentage of healthy area and survival. All laboratory experiments were carried out at the Alfred Wegener Institute in Bremerhaven, from January to July 2024. The mariculture experiment took place at the hatchery of Polaralge AS (Sandhornøy, Norway; December - February 2024) and the deployment site of Lofoten Blue Harvest (Lilje Engla, Lofoten, Norway; 68°16'02.8N 15°06'14.8E; February – June 2024).
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.
A sublittoral transect (P3) in the North of Helgoland that had been investigated ~40 years earlier by Lüning (1970) was traversed again. Scuba dives were carried out between 13.07.2005 and 25.08.2005. For each sampling point, time, date and coordinates were given as well as the depth in m mean low water spring tide. 0.25 m² frames were used to obtain the species composition, total fresh mass and total dry mass. In addition, 1 m² frames were used to record the kelp community by counting the individuals and measuring kelp stipe length, kelp blade area, kelp blade fresh mass, kelp age and fresh mass of epiphytes on the kelp stipes. Equal Location IDs represent the same frame.
The flexural rigidity and bending modulus of kelp, Laminaria hyperborea, collected at the MarGate area (https://www.awi.de/en/science/special-groups/scientific-diving/margate.html) north of Heligoland, Germany (latitude: 54° 11.700'N, longitude: 7° 52.600'E) was determined from measurements performed at the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research. Scientific divers from the Biological Institute Helgoland, AWI, collected nine kelps (Laminaria hyperborea) from the MarGate area on 21.06.2022. The collected kelps were transported into the laboratory in boxes filled with seawater from the site and stored in laboratory sinks filled with running aerated seawater from the North Sea during the experiments. The measurements were carried out on 23.06.2022, 25.06.2022, and 27.06.2022. They consisted of cutting strips 20 cm in length (L) and 2.5 cm in width (b) from the blades close to the stipe of each kelp. The cut-out strips were towel-dried, and their thickness (t, mm) and weight in grams were measured. The weight in grams was converted to weight per unit area (w, N/m²) to compute the flexural rigidity per unit width (J, Nm). A standard ruler with precision for the nearest millimeter was used to measure the length (L), width (b), and cantilever length (l) of strips. The thickness (t) of the strip was measured with a caliper gauge that measured to the nearest 0.01 millimeter. The weight of the strip was measured by a weighing scale (Sartorius, LE323S), which had a precision of 0.001 grams. The cut-out strips from each kelp form the nine samples tested for the bending properties. Each sample is used to repeat the cantilever test four times, i.e., both sides' ends, as Henry (2014) recommended to improve the accuracy. An apparatus consisting of two planes, one angled at 45° (θ = 45°) and the other parallel to the horizontal, was used for the test. The device was clamped onto a table on the horizontal plane. The experimental protocol consists of laying each strip onto the apparatus with the strip's edge coinciding with the apparatus's angled edge. After that, the strip is slowly moved forward with a ruler, with the ruler's zero coinciding with the strip's edge. This is done until the tip of the strip touches the inclined plane. The horizontal projection of the length of the hanging strip is equal to the distance between the ruler's tip and the apparatus's angle, termed the cantilever length (l). The flexural rigidity per unit width (J, Nm) and the bending modulus (Eb, N/m²) are then calculated with the second moment of area (I, m⁴) as in Henry (2014).
Over the whole water column, daily diffuse attenuation coefficient (Kd in 1/m) values are based on in situ photosynthetically active radiation (PAR) measurements performed in different depths (1.2, 2.9, 4.4, 6.6 m) during summer 2014. PAR for the algae collection depths is calculated based on daily Kd values. Daily net primary production (NPP in g C/m² seafloor/day) for each sampling depth is calculated with in situ vertical profiles based on daily Kd, leaf area index (Pehlke and Bartsch, 2008) and a photosynthetic quotient (PQ) of 1.18 (Miller III et al. 2009). For comparative purposes, daily NPP values were also calculated using the measured maximum and minimum daily Kd and the mean Kd, which were derived from all daily Kd over the entire sampling period.
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