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On 18 April 1947, British forces set off the largest non-nuclear explosion in history. The target was a small island in the North Sea, thirty miles off the German coast, which for generations had stood as a symbol of Anglo-German conflict: Heligoland. A long tradition of rivalry was to come to an end here, in the ruins of Hitler's island fortress. Pressed as to why it was not prepared to give Heligoland back, the British government declared that the island represented everything that was wrong with the Germans: 'If any tradition was worth breaking, and if any sentiment was worth changing, then the German sentiment about Heligoland was such a one'. Drawing on a wide range of archival material, Jan Ruger explores how Britain and Germany have collided and collaborated in this North Sea enclave. For much of the nineteenth century, this was Britain's smallest colony, an inconvenient and notoriously discontented outpost at the edge of Europe. Situated at the fault line between imperial and national histories, the island became a metaphor for Anglo-German rivalry once Germany acquired it in 1890.Turned into a naval stronghold under the Kaiser and again under Hitler, it was fought over in both world wars. Heavy bombardment by the Allies reduced it to ruins, until the Royal Navy re-took it in May 1945. Returned to West Germany in 1952, it became a showpiece of reconciliation, but one that continues to bear the scars of the twentieth century. Tracing this rich history of contact and conflict from the Napoleonic Wars to the Cold War, Heligoland brings to life a fascinating microcosm of the Anglo-German relationship. For generations this cliff-bound island expressed a German will to bully and battle Britain; and it mirrored a British determination to prevent Germany from establishing hegemony on the Continent. Caught in between were the Heligolanders and those involved with them: spies and smugglers, poets and painters, sailors and soldiers. Heligoland is the compelling story of a relationship which has defined modern Europe.

The story of Heligoland, the North Sea island which for generations stood as a symbol of Anglo-German conflict. A fascinating microcosm of a long and often troubled relationship, covering two centuries and two world wars.

Background Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity, and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome, and metaproteome analyses. Results Prominent active 0.2–3 µm free-living clades comprised Aurantivirga , “Formosa”, Cd . Prosiliicoccus, NS4, NS5, Amylibacter , Planktomarina , SAR11 Ia, SAR92, and SAR86, whereas BD1-7, Stappiaceae , Nitrincolaceae , Methylophagaceae , Sulfitobacter , NS9, Polaribacter , Lentimonas , CL500-3, Algibacter , and Glaciecola dominated 3–10 µm and > 10 µm particles. Particle-attached bacteria were more diverse and exhibited more dynamic adaptive shifts over time in terms of taxonomic composition and repertoires of encoded polysaccharide-targeting enzymes. In total, 305 species-level metagenome-assembled genomes were obtained, including 152 particle-attached bacteria, 100 of which were novel for the sampling site with 76 representing new species. Compared to free-living bacteria, they featured on average larger metagenome-assembled genomes with higher proportions of polysaccharide utilization loci. The latter were predicted to target a broader spectrum of polysaccharide substrates, ranging from readily soluble, simple structured storage polysaccharides (e.g., laminarin, α-glucans) to less soluble, complex structural, or secreted polysaccharides (e.g., xylans, cellulose, pectins). In particular, the potential to target poorly soluble or complex polysaccharides was more widespread among abundant and active particle-attached bacteria. Conclusions Particle-attached bacteria represented only 1% of all bloom-associated bacteria, yet our data suggest that many abundant active clades played a pivotal gatekeeping role in the solubilization and subsequent degradation of numerous important classes of algal glycans. The high diversity of polysaccharide niches among the most active particle-attached clades therefore is a determining factor for the proportion of algal polysaccharides that can be rapidly remineralized during generally short-lived phytoplankton bloom events. 9xVFsdNaK4F9f5nWnV_ZPh Video Abstract

Background Blooms of marine microalgae play a pivotal role in global carbon cycling. Such blooms entail successive blooms of specialized clades of planktonic bacteria that collectively remineralize gigatons of algal biomass on a global scale. This biomass is largely composed of distinct polysaccharides, and the microbial decomposition of these polysaccharides is therefore a process of prime importance. Results In 2020, we sampled a complete biphasic spring bloom in the German Bight over a 90-day period. Bacterioplankton metagenomes from 30 time points allowed reconstruction of 251 metagenome-assembled genomes (MAGs). Corresponding metatranscriptomes highlighted 50 particularly active MAGs of the most abundant clades, including many polysaccharide degraders. Saccharide measurements together with bacterial polysaccharide utilization loci (PUL) expression data identified β -glucans (diatom laminarin) and α -glucans as the most prominent and actively metabolized dissolved polysaccharide substrates. Both substrates were consumed throughout the bloom, with α -glucan PUL expression peaking at the beginning of the second bloom phase shortly after a peak in flagellate and the nadir in bacterial total cell counts. Conclusions We show that the amounts and composition of dissolved polysaccharides, in particular abundant storage polysaccharides, have a pronounced influence on the composition of abundant bacterioplankton members during phytoplankton blooms, some of which compete for similar polysaccharide niches. We hypothesize that besides the release of algal glycans, also recycling of bacterial glycans as a result of increased bacterial cell mortality can have a significant influence on bacterioplankton composition during phytoplankton blooms. A8iwHBb1oEC4q82u7HbzQ4 Video Abstract

The combined effects of predicted ocean acidification and global warming on the larvae of the cold-eurythermal spider crab Hyas araneus L. were investigated in 2 populations: a southernmost around Helgoland (North Sea, 54 degree N) and a northernmost at Svalbard (North Atlantic, 79 degree N). Larvae were exposed at temperatures of 3, 9 and 15 degree C to present day normocapnia (380 ppm CO sub(2)) and to CO sub(2) conditions predicted for the near or medium-term future (710 ppm by the year 2100, 3000 ppm by 2300 and beyond). Larval development time, growth and C/N ratio were studied in the larval stages Zoea I II, and Megalopa. Permanent differences in instar duration between both populations were detected in all stages, likely as a result of evolutionary temperature adaptation. With the exception of Zoea II at 3 degree C and under all CO sub(2) conditions, development in all instars from Svalbard was delayed compared to those from Helgoland. Most prominently, development was much longer and fewer specimens morphosed to the first crab instar in the Megalopa from Svalbard than from Helgoland. Enhanced CO sub(2) levels (particularly 3000 ppm) extended the duration of larval development and reduced larval growth (measured as dry mass) and fitness (decreasing C/N ratio, a proxy of the lipid content). Such effects were strongest in the zoeal stages of Svalbard larvae, and during the Megalopa instar of Helgoland larvae. The high sensitivity of megalopae from the Svalbard population to warming and of those from Helgoland to enhanced CO sub(2) levels suggests that this larval instar is a physiologically sensitive bottleneck within the life cycle of H. araneus.

Non‐tidal ocean loading (NTOL) signals are known to be a significant source of geophysically induced noise in gravimetric and geodetic observations also far‐away from the coast and especially during extreme events such as storm surges. Operationally available corrections suffer from a low temporal and spatial resolution and reveal too small amplitudes on continental stations. Dedicated high‐resolution sea‐level modeling of the North and Baltic Sea provides an improved prediction of NTOL signals. Superconducting gravimeter and Global Navigation Satellite Systems observations on the small offshore island of Heligoland in the North Sea are used for an evaluation of the model values revealing largely increased correlations of up to 0.9 and signal reductions of up to 50% during a storm surge period of one month in January and February 2022. Evaluations on additional continental superconducting gravimeter stations also show significant improvements through the recommended high‐resolution modeling for improved signal separation further away from the coast. Plain Language Summary Terrestrial gravimetry is a technique to monitor temporal variations of the gravity acceleration at the Earth's surface that are induced by mass variations and deformations caused by a large number of geophysical effects on very different temporal and spatial scales. Current applications of high social relevance are the estimation of terrestrial water storage variations under climate change conditions, for example, groundwater depletion or polar and alpine ice mass loss, as well as hazard and geothermal monitoring. Before analyzing such signals of interest, it is essential to separate all other signals included in the gravimetric observations usually on the basis of adequate models. Amongst these disturbing signals, NTOL is one of the smaller but still significant effects. Up to now, the available operational corrections show a weak correlation with gravimetric observations and their application does not lead to a significant reduction of the observational signal variation. This situation largely improves with a high‐resolution model for gravity observations on the North Sea island of Heligoland. The model results are also applied to gravity records that were observed further away from the coast to assess the benefits of the model for an improved signal separation even at continental stations. Key Points High‐resolution ocean model of the North and Baltic Sea provides improved non‐tidal ocean loading signals Model evaluation by geodetic observations on the island of Heligoland shows correlation of 0.9 and signal reduction of 50% Continental gravimetric stations further away from the coast benefit from high‐resolution model for an improved signal separation

The Helgoland Roads time series is one of the longest and most detailed time series in the world. It comprises daily phytoplankton counts accompanied by physico-chemical measurements. As such, it provides valuable long-term record of changes and their underlying causes in the phytoplankton community around Helgoland. This work provides an updated check-list of the phytoplankton species encountered at the Helgoland Roads LTER station with additional taxonomic assessments from live net samples and scanning electron microscope surveys. Since the last check-list was published 11 additional taxa have been recorded for the first time comprising 9 diatom and 2 dinoflagellate species. Of the 9 diatom species 3 were Chaetoceros species: Chaetoceros anastomosans , C. pseudocurvisetus and C. lorenzianus (the latter identified by their resting cysts) which were all first recognised in September 2009. The toxic dinoflagellate Dinophysis tripos , and the bipolar centric diatom Odontella longicruris both were first observed in September 2015. The latest new record is the potentially toxic dinoflagellate Alexandrium ostenfeldii , first recorded in August 2017. All of the first records (with the exception of Dinophysis tripos ) were first observed in semi-quantitative surveys based on live samples and SEM demonstrating that adding less frequent but very detailed assessments can complement high frequency counts of fixed samples as long as these data of different origin are linked efficiently to the individual sampling event and all metadata including representative pictorial metadata are recorded in a consistent manner. In this manner the enhanced checklist serves as a baseline against which long-term changes in phytoplankton potentially related to ecosystem state can be addressed.

Studies dealing with the effects of changing global temperatures on living organisms typically concentrate on annual mean temperatures. This, however, might not be the best approach in temperate systems with large seasonality where the mean annual temperature is actually not experienced very frequently. The mean annual temperature across a 50-year, daily time series of measurements at Helgoland Roads (54.2° N, 7.9° E) is 10.1°C while seasonal data are characterized by a clear, bimodal distribution; temperatures are around 6°C in winter and 15°C in summer with rapid transitions in spring and autumn. Across those 50 years, the temperature at which growth is maximal for each single bloom event for 115 phytoplankton species (more than 6000 estimates of optimal temperature) mirrors the bimodal distribution of the in situ temperatures. Moreover, independent laboratory data on temperature optima for growth of North Sea organisms yielded similar results: a deviance from the normal distribution, with a gap close to the mean annual temperature, and more optima either above or below this temperature. We conclude that organisms, particularly those that are short-lived, are either adapted to the prevailing winter or summer temperatures in temperate areas and that few species exist with thermal optima within the periods characterized by rapid spring warming and autumn cooling.

Reliable net primary production (NPP) estimations of kelp forests are important to evaluate their C-fixation potential. Photosynthetic oxygen measurements can be converted to C-fixation using photosynthetic quotients (PQs). Although there is a known high variability in PQs, the extent and the consequences for NPP is understudied in kelp species. Thus, the present study aimed (i) to quantify the variability of PQs, (ii) to model NPP and (iii) to assess the impact of warming on both. The kelp, Laminaria hyperborea , was studied near the island of Helgoland (North Sea, Germany) along a depth gradient (2, 4, 6 m below mean low water spring tide) across all four seasons. Blade discs were cultivated during at least 6 days per season under simulated ambient photosynthetic photon flux density (PPFD) and temperature conditions and, in parallel, in a warming scenario (+ 4°C). PQs were calculated from parallel oxygen production and 14 C-fixation measurements at saturating PPFD at the end of the incubation period. Seasonal PQs varied between 1.7 and 4.4, with highest values in summer due to increased oxygen production. The warming scenario stimulated C-fixation in most seasons, lowering the PQ in comparison to ambient temperature conditions, while collection depth had no significant effect on PQs. The seasonal PQs were used to model daily NPP rates for kelp standing stock at 4 m depth. These daily NPP rates were compared between temperature treatments and with daily NPP rates based on fixed PQs. The warming scenario had a stimulating effect on daily NPP rates in the high-light season spring. In the low-light season autumn, warming resulted in negative daily NPP rates, as the high respiration rates could not be compensated by gross photosynthesis. Overall, annual NPP rate under warming conditions (347 g C m –2 yr –1 ) was 14% higher than the annual NPP rate under ambient conditions (303 g C m –2 yr –1 ). Modelling daily NPP with fixed PQs, which neglects the seasonal variation of the PQs, led to a high overestimation of up to 255%. We, therefore, recommend modelling NPP rates not with a fixed PQ, but with seasonal PQs determined under different temperature scenarios in order to obtain reliable future predictions.

In temperate and subarctic regions of the Northern Hemisphere, green algae of the genus Blidingia are a substantial and environment-shaping component of the upper and mid-supralittoral zones. However, taxonomic knowledge on these important green algae is still sparse. In the present study, the molecular diversity and distribution of Blidingia species in the German State of Schleswig-Holstein was examined for the first time, including Baltic Sea and Wadden Sea coasts and the off-shore island of Helgoland (Heligoland). In total, three entities were delimited by DNA barcoding, and their respective distributions were verified (in decreasing order of abundance: Blidingia marginata, Blidingia cornuta sp. nov. and Blidingia minima). Our molecular data revealed strong taxonomic discrepancies with historical species concepts, which were mainly based on morphological and ontogenetic characters. Using a combination of molecular, morphological and ontogenetic approaches, we were able to disentangle previous misidentifications of B. minima and demonstrate that the distribution of B. minima is more restricted than expected within the examined area. Blidingia minima, the type of the genus name Blidingia, is epitypified within this study by material collected at the type locality Helgoland. In contrast with B. minima, B. marginata shows a higher phenotypic plasticity and is more widely distributed in the study area than previously assumed. The third entity, Blidingia cornuta sp. nov., is clearly delimited from other described Blidingia species, due to unique characters in its ontogenetic development and morphology as well as by its tufA and rbcL sequences.