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This text provides a summary of the life and work of Klaus Lüning, a prominent researcher in the field of seaweed biology. Lüning's career spanned several decades, during which he made significant contributions to the study of seaweed communities and their environmental requirements. He conducted research on the thermal requirements of seaweeds and investigated the circadian rhythms of growth in kelp species. Lüning also explored the presence of the hormone melatonin in seaweeds. Throughout his career, he supervised numerous students and collaborated with researchers from around the world. After retiring, Lüning established an algal farm and continued his research on Ulva. Unfortunately, he passed away in 2023 after battling cancer. Lüning's pioneering work and dedication to science left a lasting impact on the field of macroalgal research. [Extracted from the article]

Spores represent the most vulnerable life history stage of kelps. While UV-induced inhibition of spore germination has been readily documented, the impact of in situ underwater radiation below kelp canopies has been largely overlooked. We determined spectral composition and intensity of underwater radiation along a density gradient in an Alaria esculenta kelp forest at 3 m depth in Kongsfjorden, Svalbard. Accordingly, we set up a laboratory experiment simulating five different radiation conditions corresponding to irradiances under very dense to no canopy cover on a cloudless summer day. Spore responses (photosynthetic quantum yield, pigment and phlorotannin contents, swimming activity, and germination success) were determined after 4, 8, 16, and 24 h of exposure. In situ spectral radiation composition differed strongly from conditions applied in previous studies, which underestimated photosynthetically active radiation and overestimated UV-radiation effects. Furthermore, spore solutions differed significantly in quantum yield, pigment, and phlorotannin contents upon release. Nevertheless, spores reacted dynamically to different radiation conditions and exposure times. Highest radiation (PAR 61.8 W m−2, 1.9 W m−2 UVA, 0.01 W m−2 UVB) caused photodamage after exposure for ≥ 8 h, while intermediate radiation led to photoinhibition. Lowest radiation (PAR 0.23 W m−2, 0 W m−2 UVA, 0 W m−2 UVB) caused inconsistent reactions. There was a reduction of absolute pigment content in all treatments, but reduction rates of photosynthetic pigments were significantly different between radiation treatments. Soluble phlorotannin content decreased under all conditions but was not significantly affected by experimental conditions. High radiation reduced swimming activity of spores, but experimental conditions had almost no effect on germination success. Consequently, it seems unlikely that in situ radiation conditions negatively affect spores in present and future radiation scenarios. [ABSTRACT FROM AUTHOR]

Arctic West Spitsbergen in Svalbard is currently experiencing gradual warming due to climate change showing decreased landfast sea-ice and increased sedimentation. In order to document possible changes in 2012-2014, we partially repeated a quantitative diving study from 1996 to 1998 in the kelp forest at Hansneset, Kongsfjorden, along a depth gradient between 0 and 15 m. The seaweed biomass increased between 1996/1998 and 2012/2013 with peak in kelp biomass shifted to shallower depth, from 5 to 2.5 m. The kelp biomass at 2.5 m was 8.2-fold higher in 2012/2013 (14 kg fresh biomass m) than in 1996/1998 and mostly due to an increase in the kelp Laminaria digitata. This resulted in a very high density of 2- to 8-year-old kelp (70 ind. m) and a high leaf area index of nearly 10 at 2.5 m. The entire zonation seemed to have shifted upwards to shallower depth, since also the lower depth limit of most dominant brown algae was shallower as well as the biomass maximum of several taxa. The cumulated annual photosynthetic active radiation at 15 m depth (42 mol m year) determined the current depth limit of kelps. Changes also resulted in an altered seaweed community pattern. The complex pattern of change was probably driven by opposing effects of co-acting environmental drivers, namely lack of ice-scouring, elongation of the open-water period and deterioration of the underwater irradiance climate. The results are interpreted as a consequence of Arctic warming probably reflecting a typical scenario for change along other Arctic shores in near future. [ABSTRACT FROM AUTHOR]

Submerged marine forests of macroalgae known as kelp are one of the key structures for coastal ecosystems worldwide. These communities are responding to climate driven habitat changes and are therefore appropriate indicators of ecosystem status and health. Hyperspectral remote sensing provides a tool for a spatial kelp habitat mapping. The difficulty in optical kelp mapping is the retrieval of a significant kelp signal through the water column. Detecting submerged kelp habitats is challenging, in particular in turbid coastal waters. We developed a fully automated simple feature detection processor to detect the presence of kelp in submerged habitats. We compared the performance of this new approach to a common maximum likelihood classification using hyperspectral AisaEAGLE data from the subtidal zones of Helgoland, Germany. The classification results of 13 flight stripes were validated with transect diving mappings. The feature detection showed a higher accuracy till a depth of 6 m (overall accuracy = 80.18%) than the accuracy of a maximum likelihood classification (overall accuracy = 57.66%). The feature detection processor turned out as a time-effective approach to assess and monitor submerged kelp at the limit of water visibility depth. [ABSTRACT FROM AUTHOR]

We did a survey on macroalgal diversity along a transect off Hansneset (78°39′N, 11°57′E), Kongsfjorden, western Svalbard, between 0- and >15-m depths in 2012/2013. One major intention was to compare our data to a similar study performed in 1996/1998 at the same site and to document possible changes. We identified 58 species of macroalgae, 12 Chlorophyta, 31 Phaeophyceae, and 15 Rhodophyta. One species ( Sphacelorbus nanus) is a new record for Svalbard. Fourteen species are new records for the Kongsfjorden area. Fertile tetrasporophytes of Turnerella pennyi ( Cruoria phase) and the microscopic Chlorochytrium stage of Spongomorpha aeruginosa are also recorded for the first time from Svalbard. An increase from 20 to 45 species in the littoral in 2012/2013 compared with 1996/1998 was recorded. This study increases the total macroalgal species diversity of Kongsfjorden to 76. While 62 species were found in 1996/1998 and 58 in 2012/2013, only 42 were common to both investigations. We have made some taxonomic annotations to 20 species/genera. Strikingly, we did not find again some red algae, such as Hildenbrandia rubra, Palmaria palmata, Polysiphonia spp., or Scagelia pylaisaei, that had been recorded in 1996/1998. Possible reasons for the changes based on recent knowledge from Kongsfjorden are discussed. [ABSTRACT FROM AUTHOR]

The impact of abiotic factors on kelp sporophyte reproduction has rarely been investigated. Laminaria digitata (Hudson) J.V. Lamouroux is one of the few summer fertile Laminaria species worldwide and reproduction is subjected to relatively high water temperatures. We investigated the impact of prevailing summer temperatures (~18°C in August) on the induction of sporangia, meiospore release, and germination at the island of Helgoland ( North Sea). At Helgoland, fertile sporophytes are found between April and December with a maximum in late summer. While released meiospore numbers were constant between June and October, germination rates decreased significantly in summer. Short-term exposure of mature sori to 17°C-22°C induced a significantly higher meiospore release indicating enhancement of sporulation by elevated temperatures. Induction of sporangia on vegetative blade disks was not possible at 20°C, and fertility was only 20% at 18°C-19°C, but it was 100% in cool temperatures of 1°C-10°C. It was shown for the first time in a kelp species that 'sporogenesis' is the life-cycle process with the narrowest temperature window compared to growth or survival of the sporophyte or reproduction, growth, and survival of the gametophyte. We incorporated several parameters (induction time, fertile area, and relative fertility) into a 'Reproductive efficiency index.' This indicates that sporogenesis of L. digitata is a cold-adapted process with an optimum at (5)-10°C. The results show that the population at Helgoland is at its reproduction limit despite the existence of other geographically more southerly located populations. [ABSTRACT FROM AUTHOR]

Rising atmospheric CO2-concentrations will have severe consequences for a variety of biological processes. We investigated the responses of the green alga Ulva lactuca ( Linnaeus) to rising CO2-concentrations in a rockpool scenario. U. lactuca was cultured under aeration with air containing either preindustrial pCO2 (280 μatm) or the pCO2 predicted by the end of the 21st century (700 μatm) for 31 days. We addressed the following question: Will elevated CO2-concentrations affect photosynthesis (net photosynthesis, maximum relative electron transport rate ( rETR(max)), maximum quantum yield ( Fv/Fm), pigment composition) and growth of U. lactuca in rockpools with limited water exchange? Two phases of the experiment were distinguished: In the initial phase (day 1-4) the Seawater Carbonate System ( SWCS) of the culture medium could be adjusted to the selected atmospheric pCO2 condition by continuous aeration with target pCO2 values. In the second phase (day 4-31) the SWCS was largely determined by the metabolism of the growing U. lactuca biomass. In the initial phase, Fv/Fm and rETR(max) were only slightly elevated at high CO2-concentrations, whereas growth was significantly enhanced. After 31 days the Chl a content of the thalli was significantly lower under future conditions and the photosynthesis of thalli grown under preindustrial conditions was not dependent on external carbonic anhydrase. Biomass increased significantly at high CO2-concentrations. At low CO2-concentrations most adult thalli disintegrated between day 14 and 21, whereas at high CO2-concentrations most thalli remained integer until day 31. Thallus disintegration at low CO2-concentrations was mirrored by a drastic decline in seawater dissolved inorganic carbon and HCO3− . Accordingly, the SWCS differed significantly between the treatments. Our results indicated a slight enhancement of photosynthetic performance and significantly elevated growth of U. lactuca at future CO2-concentrations. The accelerated thallus disintegration at high CO2-concentrations under conditions of limited water exchange indicates additional CO2 effects on the life cycle of U. lactuca when living in rockpools. [ABSTRACT FROM AUTHOR]

In natural environments, marine biotas are exposed to a variety of simultaneously acting abiotic factors. Among these, temperature, irradiance and CO2 availability are major factors influencing the physiological performance of marine macroalgae. To test whether elevated levels of CO2 may remediate the otherwise reduced performance of uncalcified seaweeds under the influence of other stressful abiotic factors, we performed multi-factorial experiments with the red alga Chondrus crispus from Helgoland (North Sea) with two levels of CO2, temperature and irradiance: low and high pCO2 levels were tested in combination with either (1) optimal and low irradiances or (2) optimal and sub-lethal high temperatures for growth. Performance of C. crispus was evaluated as biomass increase and relative growth rates (RGR), gross photosynthesis and pigment content. Acclimations of growth and photosynthesis were measured after 4 and 8 days. Acclimation time was crucial for elucidating single or combined CO2 effects on growth and photosynthesis. Significant CO2 effects became evident only in combination with either elevated temperature or reduced irradiance. Growth and photosynthesis had divergent patterns: RGR and biomass significantly increased only under a combination of high pCO2 and elevated temperature; gross photosynthesis was significantly reduced under high pCO2 conditions at low irradiance. Pigment content varied in response to irradiance and temperature, but was independent of pCO2. [ABSTRACT FROM AUTHOR]

Our objective for this study was to evaluate the influence of preindustrial and expected future atmospheric CO2 concentrations (280 μatm and 700 μatm pCO2, respectively) on different life-cycle stages of the kelp Laminaria hyperborea from Helgoland (Germany, North Sea). Zoospore germination, gametogenesis, vegetative growth, sorus formation and photosynthetic performance of vegetative and fertile tissue were examined. The contribution of external carbonic anhydrase (exCA) to C-supply for net-photosynthesis (net-PS) and the Chl a- and phlorotannin content were investigated. Female gametogenesis and vegetative growth of sporophytes were significantly enhanced under the expected future pCO2. rETR(max) and net-PS of young vegetative sporophytes tended to increase performance at higher pCO2. The trend towards elevated net-PS vanished after inhibition of exCA. In vegetative sporophytes, phlorotannin content and Chl a content were not significantly affected by pCO2. [ABSTRACT FROM AUTHOR]

This review about the genus Laminaria sensu lato summarizes the extensive literature that has been published since the overview of the genus given by Kain in 1979. The recent proposal to divide the genus into the two genera Laminaria and Saccharina is acknowledged, but the published data are discussed under a 'sensu lato' concept, introduced here. This includes all species which have been considered to be 'Laminaria' before the division of the genus. In detail, after an introduction the review covers recent insights into phylogeny and taxonomy, and discusses morphotypes, ecotypes, population genetics and demography. It describes growth and photosynthetic performance of sporophytes with special paragraphs on the regulation of sporogenesis, regulation by endogenous rhythms, nutrient metabolism, storage products, and salinity tolerance. The biology of microstages is discussed separately. The ecology of these kelps is described with a focus on stress defence against abiotic and biotic factors and the role of Laminaria as habitat, its trophic interactions and its competition is discussed. Finally, recent developments in aquaculture are summarized. In conclusion to each section, as a perspective and guide to future research, we draw attention to the remaining gaps in the knowledge about the genus and kelps in general. [ABSTRACT FROM AUTHOR]

The existence of cryptic diversity in the ‘Porphyra leucosticta' complex of the North Atlantic and Mediterranean was confirmed from a wide variety of recent and over 100-year-old herbarium specimens using plastid and nuclear molecular data in combination with karyological, morphological and ecological observations. The results revealed the presence of a new species, P. olivii sp. nov., within the P. leucosticta complex. Possible evidence for sexual reproduction was observed in a culture of P. olivii from the holotype site, Gulf of Thessaloniki in Greece, where n = 2 chromosomes in male gametes and neutral spores, and 2n = 4 in zygotospores. Archeospores and neutral spores also formed in culture providing evidence for possible asexual reproduction. The results also revealed the presence of P. rosengurttii, originally described from the north-western Atlantic, in both the north-eastern Atlantic and the Mediterranean, and enabled new morphological and ecological information to be obtained for this species. The rbcL sequences for P. olivii, including from an 1889 specimen of ‘Porphyra leucosticta’, differed by one transition between the north-western Atlantic and Mediterranean. The ITS1 of the holotype of P. olivii differed by a single bp transition from another specimen from the same location. The ITS1 of specimens from the northwestern Atlantic were identical but differed by 3-4 bp substitutions from the specimens from the Mediterranean. Partial rDNA SSU sequences were identical. In P. rosengurttii, rbcL sequences, including from specimens dated 1890 and 1906, differed by a single transition between both regions, the ITS1 had 92–100% similarity and partial rDNA SSU sequences were identical. Our study indicates that molecular, morphological and ecological evidence from a wide variety of samples (recent and old) and locations should be investigated before a new species is erected. The molecular comparison with old herbarium specimens also revealed that P. olivii and P. rosengurttii are not recent invaders to the Mediterranean but have been present for at least 100 years. [ABSTRACT FROM AUTHOR]

The Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience a continuous increase in seawater temperature and glacial melt while sea‐ice cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species diversity were quantified at the study site Hansneset, Kongsfjorden (W‐Spitsbergen) in order to identify potential changes over time. In 2021, we repeated the earlier studies by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0, 2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2 at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the depth transect in 2021 was not significantly different compared to 2012/2013, the digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed into an Alaria esculenta‐dominated kelp forest. Consequently, a pronounced shift in kelp forest structure occurred over time as we demonstrate that biomass allocation to thallus parts is kelp species‐specific. Over the past decade, kelp demography changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth limits of all dominant brown algae declined noticeably over the last 25 years while the red algal flora abundance remained unchanged at depth. We propose that the major factor driving the observed changes in the macroalgal community are alterations in underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance since 2012 and 2017, respectively. As a consequence, the interplay between kelp forest retreat to lower depth levels caused by coastal darkening and potential macroalgal biomass gain with increasing temperatures will possibly intensify in the future with unforeseen consequences for melting Arctic coasts and fjord ecosystem services. [ABSTRACT FROM AUTHOR]

The temperature tolerances of 24 tropical rnacroalgae collected on Hainan Island (P.R. China) were investigated. For some isolates, growth response curves were also determined. The upper survival temperatures (USTs, 32-37 °C) of these tropical west Pacific strains are similar to those of tropical Atlantic species. With regard to their lower survival temperatures (LSTs) the species investigated show high variations: 12 species have LSTs between 16 and 7 °C (Hypnea musciformis (Wulfen) Lamx. var esperi J. Ag., Centroceras clavulatum (C. Ag) Mont., Falkenbergia hillebrandii (Bornet) Falkenberg, Geli-diopsis intricata (Ag.) Vickers, Halymenia maculata J. Ag., Hypnea cenomyce J. Ag., Hypnea spinelfa (C. Ag.) Kütz., Gracilaria changii (Xia et Abott) Abott, Chang et Xia, Dictyopteris repens (Okam.) Boerg., Laurencia cartilaginea Yamada, Gelidium pushillum (Stackh.) Le Jol., Laurencia sp.). Their LSTs and temperature requirements for growth (range: 15-30 °C, optimum: 25-30 °C) are mostly similar to those of tropical west Atlantic and amphi-Atlantic (sub)tropical macroalgae as well as to tropical iso-lates of species with an Atlantic tropical to warm- temperate distribution. The remaining 12 species have LSTs between 6 and ≤ 1 °C (Ulva conglobata Kiellm., Ulva fasciata Delile, Padina boryana Thivy, Dictyosphaeria cavernosa (Forssk.) Boerg., Boodlea composita (Harv.) Brand, Boergesenia forbesii (Harv.) Feldm., Cladophora vagabunda (L.) van den Hoek, Enteromorpha compressa (L.) Grev., Entero-morpha intestinalis (L.) Link, Gracilaria tenuistipi-tata Chang et Xia var liui Chang et Xia, Monastroma nitidum Wittr. and Valonia aegagropila C. Ag.). Their LSTs are mostly similar to those of Atlantic macro- algae with a tropical to (warm-) temperate distribution. The results are discussed with respect to the factors which may have triggered the development of the temperature requirements of the various species. [ABSTRACT FROM AUTHOR]

Kelps are important providers and constituents of marine ecological niches, the coastal kelp forests. Kelp species have differing distribution ranges, but mainly thrive in temperate and arctic regions. Although the principal factors determining biogeographic distribution ranges are known, genomics could provide additional answers to this question. We sequenced DNA from two Laminaria species with contrasting distribution ranges, Laminaria digitata and Laminaria solidungula. Laminaria digitata is found in the Northern Atlantic with a southern boundary in Brittany (France) or Massachusetts (USA) and a northern boundary in the Arctic, whereas L. solidungula is endemic to the Arctic only. From the raw reads of DNA, we reconstructed both chloroplast genomes and annotated them. A concatenated data set of all available brown algae chloroplast sequences was used for the calculation of a robust phylogeny, and sequence variations were analyzed. The two Laminaria chloroplast genomes are collinear to previously analyzed kelp chloroplast genomes with important exceptions. Rearrangements at the inverted repeat regions led to the pseudogenization of ycf37 in L. solidungula, a gene possibly required under high light conditions. This defunct gene might be one of the reasons why the habitat range of L. solidungula is restricted to lowlight sublittoral sites in the Arctic. The inheritance pattern of single nucleotide polymorphisms suggests incomplete lineage sorting of chloroplast genomes in kelp species. Our analysis of kelp chloroplast genomes shows that not only evolutionary information could be gleaned from sequence data. Concomitantly, those sequences can also tell us something about the ecological conditions which are required for species well‐being. [ABSTRACT FROM AUTHOR]

The genus Ulva is globally distributed and has been thoroughly studied because of its functional biochemical composition, rapid growth rates and opportunistic features, and interest in Ulva cultivation is growing worldwide. In Europe, mostly near- and on-shore flow-through cultivation systems are used and land-based recirculating aquaculture systems (RAS) using fresh water or artificial seawater have not been developed for Ulva. While RAS provides quality control and can be located inland, maintenance costs are high. Using selected strains adapted to low-salinity could reduce seawater production costs and improve the economic feasibility. Therefore, our study assessed how salinity can be used as a tool for strain selection and optimization of functional traits. Growth rates and antioxidant activity of three species (four strains) of tubular and foliose Ulva from the NE-Atlantic and Mediterranean (foliose: Ulva lacinulata – two geographical strains, tubular: Ulva linza and Ulva flexuosa) were followed for three weeks at salinities ranging from 10 to 30 PSU. The tubular strains achieved optimal growth at a lower salinity than U. lacinulata. However, growth rates of both foliose strains were higher than of tubular strains, even at sub-optimal salinity. Therefore, U. lacinulata is a good candidate for RAS with artificial seawater, and the cost of salt can be reduced by up to 33.3% (20 PSU) without significantly reducing the growth rate of U. lacinulata. Higher antioxidant activity was achieved by reducing the salinity to 10 PSU for 10 days, suggesting that the functional traits of cultivated Ulva lacinulata can be optimized prior to harvest. [ABSTRACT FROM AUTHOR]

The analysis of biological and ecological traits has a long history in evolutionary and ecological research. However, trait data are often scattered and standardised terminology that transcends taxonomic and biogeographical context are generally missing. As part of the development of a global trait database of marine species, we collated trait information for European seaweeds and structured the data within the standardised framework of the World Register of Marine Species (WoRMS). We collected 45 175 trait records for 21 biologically and ecologically relevant traits of seaweeds. This resulted in a trait database for 1745 European seaweed species of which more than half (56 %) of the records were documented at the species level, while the remaining 44 % were documented at a higher taxonomic level and subsequently inherited at lower levels. The trait database for European seaweeds will serve as a foundation for future research on diversity and evolution of seaweeds and their responses to global changes. The data will contribute to developing detailed trait-based ecosystem models and will be an important tool to inform marine conservation policies. The data are publicly accessible through the AlgaeTraits portal, 10.14284/574 (AlgaeTraits, 2022). [ABSTRACT FROM AUTHOR]

Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE‐Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (Kd) between 0.28 and 0.87 m−1. Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted Kd to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3–4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m−2 seafloor · d−1 for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines. [ABSTRACT FROM AUTHOR]

The brown algae Desmarestia menziesii and D. anceps form dense underwater forests at the Western Antarctic Peninsula (WAP) in the upper to mid subtidal and play an important role in this coastal ecosystem. Seawater temperatures at the WAP increased by about 2 °C in the last 50 years and probably will rise further in future due to global warming. This may have consequences for the physiological performance and community interactions of these cold water adapted algae. In laboratory experiments with culture material we investigated the influence of increased temperatures on the photosynthetic response, growth and interspecific competition of both species. Increased temperature (5 °C) induced a higher growth rate of D. anceps and a higher optimum quantum yield of photosynthesis in both species compared to 0 °C. Neither interspecific competition nor interactions between competition and temperature were detected. The photosynthetic performance (rETRmax, α and Ek) of D. menziesii was significantly more often affected by temperature increases than of D. anceps. It was shown that a temperature increase from 0 °C to 5 °C was not harmful for both Desmarestia species in this set-up. Generally, growth of D. menziesii was very low possibly reflecting a dormancy state under continuous long-day conditions and thereby may have masked the influence of temperature on growth. In order to determine realistic survival thresholds of these key species of the Antarctic coastal ecosystem under global change scenarios, further multifactorial experiments are of great importance, including field material, different algal life stages and reproductive processes. [ABSTRACT FROM AUTHOR]

Kelp forests are important habitats in the strongly environmentally and seasonally variable Arctic. There is a critical lack of knowledge about how seasonal conditions and climate change scenarios influence survival and reproduction of kelp early life stages. To better understand the regulation of kelp life cycle processes in this harsh environment we focused on the physiological performance and reproductive success of early life stages in Alaria esculenta and Laminaria digitata from Kongsfjorden, Spitsbergen. Gametophyte growth and survival during Arctic winter and subsequent sporophyte recruitment under spring conditions were investigated. Winter conditions (2°C, complete darkness) halted gametophyte growth and prevented the onset of gametogenesis in both species. The gametophytes of L. digitata but not A. esculenta became fertile after returning to spring conditions, suggesting that sporogenesis, sexual reproduction and recruitment in A. esculenta must occur successively during summer/autumn while in L. digitata a new generation of sporophytes could develop from over-wintering gametophytes. The effects of simulated canopy shading (offering protection against extreme irradiance stress, particularly as sea ice retreats), present-day and projected Arctic summer seawater temperatures, and nutrient levels on gametophyte survival, fertility and sporophyte recruitment success were also investigated in both species. A. esculenta gametophytes had greater survival and reproductive success than L. digitata, except under very low light (simulating dense canopy). In contrast, shading was required for reproductive success in L. digitata gametophytes. Predicted summer temperatures of 9°C reduced sexual reproduction in both species. Interactions observed between these environmental drivers probably reflect species-specific seasonal patterns of survival and reproduction. These differences between kelp species in response to abiotic factors and light levels (simulated canopy shading) suggest that climate change could alter community structure in the Arctic through effects on sexual reproduction and sporophyte recruitment success. HIGHLIGHTS• Gametophytes were able to endure long periods of darkness.• Parental kelp canopy is key for gametophyte survival and recruitment.• Climate change may alter kelp recruitment patterns. [ABSTRACT FROM AUTHOR]

The analysis of biological and ecological traits has a long history in evolutionary and ecological research. However, trait data are often scattered and standardised terminology that transcends taxonomic and biogeographical context are generally missing. As part of the development of a global trait database of marine species, we collated trait information for European seaweeds and structured the data within the standardised framework of the World Register of Marine Species (WoRMS). We collected 45,175 records for 21 biologically and ecologically relevant traits of seaweeds. This resulted in a trait database for 1,745 European seaweed species of which more than half (56%) of the records were documented at the species level, while the remaining 44% was documented at a higher taxonomic level and subsequently inherited at lower levels. The trait database for European seaweeds will serve as a foundation for future research on diversity and evolution of seaweeds, and their responses to global changes. The data will contribute to developing detailed trait-based ecosystem models, and will be an important tool to inform marine conservation policies. The data is publicly accessible through the AlgaeTraits portal, algaetraits.org, doi: https://doi.org/10.14284/574, (AlgaeTraits, 2022). [ABSTRACT FROM AUTHOR]

In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords. [ABSTRACT FROM AUTHOR]

Endemic Antarctic macroalgae are especially adapted to live in extreme Antarctic conditions. Their potential biogeographic distribution niche is primarily controlled by the photoperiodic regime and seawater temperatures, since these parameters regulate growth, reproduction, and survival during the entire life cycle. Here we analyzed the upper survival temperature (UST) of juvenile sporophytes and the temperature range for sporophyte formation from gametophytes of Desmarestia menziesii, one of the dominant endemic Antarctic brown algal species. This process is a missing link to better evaluate the full biogeographical niche of this species. Two laboratory experiments were conducted. First, growth and maximum quantum yield of juvenile sporophytes were analyzed under a temperature gradient (0, 5, 10, 12, 13, 14, 15, and 16 °C) in a 16:8 h light:dark (LD) regime (Antarctic spring condition) for 2 weeks. Second, the formation of sporophytes from gametophytes (as a proxy of gametophyte reproduction) was evaluated during a 7 weeks period under a temperature gradient (0, 4, 8, 12, and 16 °C), and two different photoperiods: 6:18 h LD regime simulating winter conditions and a light regime simulating the Antarctic shift from winter to spring by gradually increasing the light period from 7.5:16.5 h LD (late winter) to 18.5:5.5 h LD (late spring). Sporophytes of D. menziesii were able to grow and survive up to 14 °C for 2 weeks without visible signs of morphological damage. Thus, this species shows the highest UST of all endemic Antarctic Desmarestiales species. In turn, gametophyte reproduction solely took place at 0 °C but not at 4–8 °C. The number of emerging sporophytes was six times higher under the light regime simulating the transition from winter to spring than under constant short day winter conditions. There was a negative relationship between the number of sporophytes formed and the gametophyte density at the beginning of the experiment, which provides evidence that gametophyte density exerts some control upon reproduction in D. menziesii. Results strongly indicate that although sporophytes and gametophytes may survive in warmer temperatures, the northernmost distribution limit of D. menziesii in South Georgia Islands is set by the low temperature requirements for gametophyte reproduction. Hence, global warming could have an impact on the distribution of this and other Antarctic species, by influencing their growth and reproduction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Presentation of a laboratory experiment for analysis of reflectance spectra of marine macroalgae. [•] At the higher taxonomic group level, spectral mixture of macroalgae is linear. [•] Inner-group spectral similarity is high; therefore unmixing can hardly be performed. [•] Sub-pixel analysis of macroalgae is feasible to a limited extend. [Copyright &y& Elsevier]

Analysis of coastal marine algae communities enables us to adequately estimate the state of coastal marine environments and provides evidence for environmental changes. Hyperspectral remote sensing provides a tool for mapping macroalgal habitats if the algal communities are spectrally resolvable. We compared the performance of three classification approaches to determine the distribution of macroalgae communities in the rocky intertidal zone of Heligoland, Germany, using airborne hyperspectral (AISAeagle) data. The classification results of two supervised approaches (maximum likelihood classifier and spectral angle mapping) are compared with an approach combining k-Means classification of derivative measures. We identified regions of different slopes between main pigment absorption features of macroalgae and classified the resulting slope bands. The maximum likelihood classifier gained the best results (Cohan's kappa = 0.81), but the new approach turned out as a time-effective possibility to identify the dominating macroalgae species with sufficient accuracy (Cohan's kappa = 0.77), even in the heterogeneous and patchy coverage of the study area. [ABSTRACT FROM AUTHOR]

To study the effect of different radiation conditions on sporogenesis of Laminaria digitata (Huds.) J. V. Lamour., excised disks were induced to form sporangia under PAR (P), PAR + ultraviolet-A (UVA) (PA), and PAR + UVA + ultraviolet-B (UVB) (PAB) conditions in the laboratory. Vitality of meiospores, released from sori induced under different radiation conditions in the laboratory and from sori of wild sporophytes acclimated to in situ solar radiation in the presence and absence of ultraviolet radiation (UVR), was measured in terms of their germination capacity. Sorus induction in disks of laboratory-grown sporophytes was not hampered under light supplemented with UVR, and sorus area was not significantly different among P, PA, and PAB. Vitality and germination rate of meiospores released from sori induced under different radiation treatments was comparable. Likewise, screening of UVR of the natural solar radiation did not promote higher germination rates of meiospores released from wild sporophytes. Germination rates were, however, higher in meiospores released from laboratory-induced sori compared to sori of wild sporophytes. Higher DNA damage (formation of cyclobutane pyrimidine dimers, CPDs) was observed in laboratory-grown nonsorus compared to sorus tissue, while CPDs were nondetectable in both sorus and nonsorus tissue of wild sporophytes. To explain the apparent protection of developing meiospores and the unexpected UV resistance of soral tissue, concurrent anatomical investigations of sporogenic tissue were performed. We observed the previously unreported existence of two types of sterile paraphysis cells. One type of paraphysis cells, the most frequent type, contained several red-fluorescing plastids. The other type, less frequently occurring, was completely filled with substances emitting blue fluorescence under violet excitation, presumably brown algal phenolic compounds (phlorotannins). Cells of this type were irregularly scattered within the sorus and did not contain red-fluorescing plastids. Meiospore-containing sporangia were positioned embedded between both types of paraphysis cells. In vegetative tissue, blue autofluorescence was observed only in injured parts of the blade. Results of our study suggest that the sorus structure with phlorotannins localized in the specialized paraphysis cells may be able to screen harmful UVR and protect UV-sensitive meiospores inside the sporangia. [ABSTRACT FROM AUTHOR]

Temperature is one of the most important factors controlling the biogeographic distribution of seaweeds and is expected to increase due to the rise in anthropogenic greenhouse gas concentrations, especially in polar and cold-temperate regions. To estimate prospective distributional shifts in cold-water key structural seaweeds from both hemispheres, we related temperature requirements and recent distributions of seaweeds to observed mean sea surface temperature (SST) isotherms for the periods 1980–1999 (Meteorological Office Hadley Centre's SST data set; HadISST) and to modelled temperatures for 2080–2099 [Coupled Model Intercomparison Project 3 (CMIP3) database prepared for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) report] based on moderate greenhouse gas emissions Special Report on Emission Scenarios – Scenario B1 (SRESA1B). Under this scenario, North Atlantic polar to cold-temperate seaweeds investigated will extend their distribution into the High Arctic until the end of the 21st century, but retreat along the northeastern Atlantic coastline. In contrast, selected Antarctic seaweeds will probably not significantly alter their latitudinal distributions, as deduced from our presently incomplete knowledge of their temperature requirements. We identified several cold-temperate regions where seaweed composition and abundance will certainly change with elevated temperatures. The results are discussed in the context of local temperature conditions, effects of multifactorial abiotic and biotic interactions and expected ecological consequences for seaweed-dominated ecosystems. [ABSTRACT FROM AUTHOR]

Two morphologically similar digitate kelp species, Laminaria digitata and Hedophyllum nigripes, co-occur along a shallow sublittoral depth gradient in the Arctic but, in contrast to L. digitata, very few ecophysiological data exist for H. nigripes. We investigated growth, survival, photosynthetic characteristics and carbon:nitrogen ratios of juvenile sporophytes, and recruitment and survival of gametophytes in genetically verified Arctic isolates of both species along temperature gradients (0–25 °C) over 14 days. Laminaria digitata gametophytes survived 23–24 °C, while sporophytes survived 21–22 °C. Hedophyllum nigripes had lower temperature affinities. Gametophytes survived 19–21 °C, while sporophytes survived 18 °C. Male gametophytes were more heat-tolerant than female gametophytes in both species. The pronounced cold adaption of H. nigripes compared to L. digitata also became apparent in different sporophyte growth optima (L. digitata: 15 °C; H. nigripes: 10 °C) and gametogenesis optima (L. digitata: 5–15 °C; H. nigripes: 0–10 °C). Higher carbon:nitrogen ratios in H. nigripes suggest an adaptation to nutrient poor Arctic conditions. The overall temperature performance of H. nigripes possibly restricts the species to Arctic–Sub-Arctic regions, while Arctic L. digitata behaved similarly to cold-temperate populations. Our data suggest that a future increase in seawater temperatures may hamper the success of H. nigripes and favour L. digitata in Arctic environments. [ABSTRACT FROM AUTHOR]

Kelp species (Laminariales, Phaeophyceae) are globally widespread along temperate to Polar rocky coastal lines. Here we analyse the mitochondrial and chloroplast genomes of Laminaria rodriguezii , in comparison to the organellar genomes of other kelp species. We also provide the complete mitochondrial genome sequence of another endemic kelp species from a Polar habitat, the Arctic Laminaria solidungula. We compare phylogenetic trees derived from twenty complete mitochondrial and seven complete chloroplast kelp genomes. Interestingly, we found a stretch of more than 700 bp in the mitochondrial genome of L.rodriguezii , which is not present in any other yet sequenced member of the Phaeophyceae. This stretch matches a protein coding region in the mitochondrial genome from Desmarestia viridis , another brown seaweed. Their high similarity suggests that these sequences originated through independent introduction into the two species. Their origin could have been by infection by yet unknown similar mitoviruses, currently only known from fungi and plants. • We present three newly sequenced organellar genomes from the kelp species Laminaria rodriguezii and Laminaria solidungula. • Their specific features and phylogenetic information content is analysed and compared to other kelp organellar genomes. • Collinearity of the organellar genomes within the kelps make them apt as robust phylogenetic markers for the entire order. • We found an independent introduction of homologous nucleotide sequences into two brown algal mitochondrial genomes. • Their potential mitovirus origin is unprecedented and should be the beginning of endeavours to search for similar sequences. [ABSTRACT FROM AUTHOR]

SUMMARY The sugar kelp Saccharina latissima experiences a wide range of environmental conditions along its geographical and vertical distribution range. Temperature and salinity are two critical drivers influencing growth, photosynthesis and biochemical composition. Moreover, interactive effects might modify the results described for single effects. In shallow water coastal systems, exposure to rising temperatures and low salinity are expected as consequence of global warming, increased precipitation and coastal run‐off. To understand the acclimation mechanisms of S. latissima to changes in temperature and salinity and their interactions, we performed a mechanistic laboratory experiment in which juvenile sporophytes from Brittany, France were exposed to a combination of three temperatures (0, 8 and 15°C) and two salinity levels (20 and 30 psu (practical salinity units)). After a temperature acclimation of 7 days, sporophytes were exposed to low salinity (20 psu) for a period of 11 days. Growth, and maximal quantum yield of photosystem II (Fv/Fm), pigments, mannitol content and C:N ratio were measured over time. We report for the first time in S. latissima a fivefold increase in the osmolyte mannitol in response to low temperature (0°C) compared to 8 and 15°C that may have ecological and economic implications. Low temperatures significantly affected all parameters, mostly in a negative way. Chlorophyll a, the accessory pigment pool, growth and Fv/Fm were significantly lower at 0°C, while the de‐epoxidation state of the xanthophyll cycle was increased at both 0 and 8°C compared to 15°C. Mannitol content and growth decreased with decreased salinity; in contrast, pigment content and Fv/Fm were to a large extent irresponsive to salinity. In comparison to S. latissima originating from an Arctic population, despite some reported differences, this study reveals a remarkably similar impact of temperature and salinity variation, reflecting the large degree of adaptability in this species. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is a unique ecosystem hosting a biodiversity that has not yet been elucidated in full detail. There is increasing evidence that there are more kelp species constricted to Arctic/sub‐Arctic habitats hitherto not well investigated, such as Hedophyllum nigripes, which is morphologically very similar to cold‐temperate Laminaria digitata. Hedophyllum nigripes was originally described as L. nigripes by Agardh from Spitsbergen but has often been misidentified as L. digitata in the European Arctic. We initiated a systematic algal survey along a depth gradient (0–7.5 m) in Kongsfjorden (Spitsbergen) in June and July 2015 and thereby confirmed a predominant presence of H. nigripes (73%). Hedophyllum nigripes is occurring between 0 and 7.5 m while L. digitata was most abundant at 2.5 m depth. Hedophyllum nigripes individuals were generally younger (2.3 vs. 3.6 years) and stipe and blade length shorter (31 vs. 54 cm and 76 vs. 96 cm, respectively) compared to L. digitata. A combination of molecular (COI‐5P) and morpho‐anatomical tools (presence of sori and mucilage ducts in the stipe) was used to differentiate specimens of H. nigripes and L. digitata. Both kelp species were indistinguishable in most cases by external blade and stipe morphology. The different blade shapes represented different ontogenetic stages rather than phenotypic plasticity. The presence of mucilage ducts in the stipe was correlated with H. nigripes and changed with depth from 17%, 36%, and 85% at 2.5, 5, and 7.5 m, respectively. In addition, all summer fertile specimens were L. digitata. [ABSTRACT FROM AUTHOR]

To understand the thermal plasticity of a coastal foundation species across its latitudinal distribution, we assess physiological responses to high temperature stress in the kelp Laminaria digitata in combination with population genetic characteristics and relate heat resilience to genetic features and phylogeography. We hypothesize that populations from Arctic and cold‐temperate locations are less heat resilient than populations from warm distributional edges. Using meristems of natural L. digitata populations from six locations ranging between Kongsfjorden, Spitsbergen (79°N), and Quiberon, France (47°N), we performed a common‐garden heat stress experiment applying 15°C to 23°C over eight days. We assessed growth, photosynthetic quantum yield, carbon and nitrogen storage, and xanthophyll pigment contents as response traits. Population connectivity and genetic diversity were analyzed with microsatellite markers. Results from the heat stress experiment suggest that the upper temperature limit of L. digitata is nearly identical across its distribution range, but subtle differences in growth and stress responses were revealed for three populations from the species' ecological range margins. Two populations at the species' warm distribution limit showed higher temperature tolerance compared to other populations in growth at 19°C and recovery from 21°C (Quiberon, France), and photosynthetic quantum yield and xanthophyll pigment responses at 23°C (Helgoland, Germany). In L. digitata from the northernmost population (Spitsbergen, Norway), quantum yield indicated the highest heat sensitivity. Microsatellite genotyping revealed all sampled populations to be genetically distinct, with a strong hierarchical structure between southern and northern clades. Genetic diversity was lowest in the isolated population of the North Sea island of Helgoland and highest in Roscoff in the English Channel. All together, these results support the hypothesis of moderate local differentiation across L. digitata's European distribution, whereas effects are likely too weak to ameliorate the species' capacity to withstand ocean warming and marine heatwaves at the southern range edge. [ABSTRACT FROM AUTHOR]

The plasticity of different kelp populations to heat stress has seldom been investigated excluding environmental effects due to thermal histories, by raising a generation under common garden conditions. Comparisons of populations in the absence of environmental effects allow unbiased quantification of the meta-population adaptive potential and resolution of population-specific differentiation. Following this approach, we tested the hypothesis that genetically distinct arctic and temperate kelp exhibit different thermal phenotypes, by comparing the capacity of their microscopic life stages to recover from elevated temperatures. Gametophytes of Laminaria digitata (Arctic and North Sea) grown at 15°C for 3 years were subjected to common garden conditions with static or dynamic (i.e., gradual) thermal treatments ranging between 15 and 25°C and also to darkness. Gametophyte growth and survival during thermal stress conditions, and subsequent sporophyte recruitment at two recovery temperatures (5 and 15°C), were investigated. Population-specific responses were apparent; North Sea gametophytes exhibited higher growth rates and greater sporophyte recruitment than those from the Arctic when recovering from high temperatures, revealing differential thermal adaptation. All gametophytes performed poorly after recovery from a static 8-day exposure at 22.5°C compared to the response under a dynamic thermal treatment with a peak temperature of 25°C, demonstrating the importance of gradual warming and/or acclimation time in modifying thermal limits. Recovery temperature markedly affected the capacity of gametophytes to reproduce following high temperatures, regardless of the population. Recovery at 5°C resulted in higher sporophyte production following a 15°C and 20°C static exposure, whereas recovery at 15°C was better for gametophyte exposures to static 22.5°C or dynamic heat stress to 25°C. The subtle performance differences between populations originating from sites with contrasting local in situ temperatures support our hypothesis that their thermal plasticity has diverged over evolutionary time scales. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ocean warming can mediate species interactions and provoke changes in community structure worldwide. Species interactions vary along environmental gradients and life-history stages and increasing temperatures may change competitive dominance between species. Kelps, being marine foundation species, have a complex heteromorphic life cycle, with the early developmental stages being a bottleneck for successful establishment of the adult population. Here, we investigated how temperature influences interactions in early life-history stages of two kelp species with different thermal affinities (Alaria esculenta and Laminaria digitata from Spitsbergen) by cultivating them in mono- and co-culture and different temperatures. Irrespectively of cultivation treatment, spore germination, gametogenesis, and sporophyte development of both species were mostly positively stimulated by a temperature increase from mean ambient summer temperatures (4–5 °C) to a global warming scenario for the Arctic future (9–10 °C) but not at 15 °C which is the southern temperature limit of A. esculenta. At 15 °C gametogenesis and sporophyte formation of A. esculenta were greatly inhibited in monoculture but not so in L. digitata. On the other hand at 5 °C and 10 °C, gametogenesis and sporophyte growth were generally faster in A. esculenta than in L. digitata, leading to a competitive advantage of A. esculenta over L. digitata in the co-cultivation treatments. The interactive effects of co-cultivation and temperature were evident, where development of A. esculenta was accelerated in the presence of L. digitata at 9 °C but not at 4 °C. Although the mechanisms triggering interspecific interactions were not determined in this study, future global warming was found to give competitive advantage of A. esculenta over L. digitata, which could affect community structure and dominance in coastal environments. [ABSTRACT FROM AUTHOR]

Background: Kelps (Laminariales, Phaeophyceae) are brown macroalgae of utmost ecological, and increasingly economic, importance on temperate to polar rocky shores. Omics approaches in brown algae are still scarce and knowledge of their acclimation mechanisms to the changing conditions experienced in coastal environments can benefit from the application of RNA-sequencing. Despite evidence of ecotypic differentiation, transcriptomic responses from distinct geographical locations have, to our knowledge, never been studied in the sugar kelp Saccharina latissima so far. Results: In this study we investigated gene expression responses using RNA-sequencing of S. latissima from environments with contrasting temperature and salinity conditions – Roscoff, in temperate eastern Atlantic, and Spitsbergen in the Arctic. Juvenile sporophytes derived from uniparental stock cultures from both locations were pre-cultivated at 8 °C and SA 30. Sporophytes acclimated to 0 °C, 8 °C and 15 °C were exposed to a low salinity treatment (SA 20) for 24 h. Hyposalinity had a greater impact at the transcriptomic level than the temperature alone, and its effects were modulated by temperature. Namely, photosynthesis and pigment synthesis were extensively repressed by low salinity at low temperatures. Although some responses were shared among sporophytes from the different sites, marked differences were revealed by principal component analysis, differential expression and GO enrichment. The interaction between low temperature and low salinity drove the largest changes in gene expression in sporophytes from Roscoff while specimens from Spitsbergen required more metabolic adjustment at higher temperatures. Moreover, genes related to cell wall adjustment were differentially expressed between Spitsbergen and Roscoff control samples. Conclusions: Our study reveals interactive effects of temperature and salinity on transcriptomic profiles in S. latissima. Moreover, our data suggest that under identical culture conditions sporophytes from different locations diverge in their transcriptomic responses. This is probably connected to variations in temperature and salinity in their respective environment of origin. The current transcriptomic results support the plastic response pattern in sugar kelp which is a species with several reported ecotypes. Our data provide the baseline for a better understanding of the underlying processes of physiological plasticity and may help in the future to identify strains adapted to specific environments and its genetic control. [ABSTRACT FROM AUTHOR]

Kelps are globally important bioengineering species with high ecological and economic value, but are increasingly threatened by climate-driven geographic range shifts. The inheritance of economically important traits from parents to offspring is poorly understood in kelps but it is of utmost interest to seaweed farmers wishing to select strains with superior performance and resilience to environmental change. For two allopatric kelp species (N-Atlantic Laminaria digitata and S-Atlantic L. pallida), we compared the speed of gametogenesis and reproductive success in parental gametophytes, and produced intraspecific and reciprocal interspecific crosses of female × male gametophyte parents isolated from the two species. We then compared the upper thermal resilience of microscopic and macroscopic sibling sporophytes in an exposure experiment over two weeks. The upper thermal limit of the sporophytes resulting from intraspecific crosses of the two species deviated by 1°C. In contrast, sporophytes from both interspecific hybrid crosses had a 2–3°C higher upper thermal tolerance than single species sporophytes, indicating heterosis for thermal tolerance. This phenotypic response appears partially sex-dependent in our study, with female parents being more important in determining the thermal-response phenotype than male parents. The presence of male gametophytes generally enhanced female reproductive success. Both gametogenesis rate and reproductive success differed among the types of reciprocal crosses. Although the interspecific crosses were artificial in an ecological sense, they may provide a tool for understanding the molecular basis of heterosis and thermal tolerance in kelps (e.g. by investigating species-specific gene expression), or for aquaculture breeding programmes against a background of rapid environmental change. [ABSTRACT FROM AUTHOR]

In haplodiplontic lineages, sexual reproduction occurs in haploid parents without meiosis. Although widespread in multicellular lineages such as brown algae (Phaeophyceae), haplodiplontic gametogenesis has been little studied at the molecular level. We addressed this by generating an annotated reference transcriptome for the gametophytic phase of the sugar kelp, Saccharina latissima. Transcriptional profiles of microscopic male and female gametophytes were analysed at four time points during the transition from vegetative growth to gametogenesis. Gametogenic signals resulting from a switch in culture irradiance from red to white light activated a core set of genes in a sex-independent manner, involving rapid activation of ribosome biogenesis, transcription and translation related pathways, with several acting at the post-transcriptional or post-translational level. Additional genes regulating nutrient acquisition and key carbohydrate-energy pathways were also identified. Candidate sex-biased genes under gametogenic conditions had potentially key roles in controlling female- and male-specific gametogenesis. Among these were several sex-biased or -specific E3 ubiquitin-protein ligases that may have important regulatory roles. Females specifically expressed several genes that coordinate gene expression and/or protein degradation, and the synthesis of inositol-containing compounds. Other female-biased genes supported parallels with oogenesis in divergent multicellular lineages, in particular reactive oxygen signalling via an NADPH-oxidase. Males specifically expressed the hypothesised brown algal sex-determining factor. Male-biased expression mainly involved upregulation of genes that control mitotic cell proliferation and spermatogenesis in other systems, as well as multiple flagella-related genes. Our data and results enhance genome-level understanding of gametogenesis in this ecologically and economically important multicellular lineage. [ABSTRACT FROM AUTHOR]

Kelp-derived detritus is a potential food item at the base level of marine food webs. A good knowledge of the factors that influence stable isotope composition in kelps is essential for reliable food web models. The variation of stable isotope signatures was analysed in three species of kelp in Kongsfjorden, Svalbard. Between 15 and 2.5 m depth, towards higher photon fluence rate, Alaria esculenta was gradually enriched in 13C while 15N did not change. The carbon/nitrogen ratio decreased with depth. 2- and 3-year-old kelp individuals had significantly higher δ15N values in their blades than 5- and 6-year-old ones. C/N ratio in blades remained statistically the same over the range of 2–6 years old plants. A two-way ANOVA did not show any interactive effects between depth and age group. A. esculenta as well as Saccharina latissima and Laminaria digitata exhibited enrichment in heavy carbon isotopes in the blades compared to the stipes, while within each species, δ15N values remained the same between blades and stipes. A more detailed analysis of kelp blades showed that independent of location in the fjord, year or season, and species, young tissue was more enriched in 13C than meristem and that decaying apical tissue was depleted relative to young tissue. The degree of this 13C depletion varied with kelp species. Meristem tissue appeared most uniform in the blades compared to young and decaying tissues and its δ13C signature was characteristic for each species with no significant difference in δ15N values. Decaying tissue showed no difference in δ13C between species. Carbon and nitrogen contents along the blades were species-specific and varied with growing location and year or season. Some advice is given on the temporal, spatial, and tissue-related choice of samples for different research objectives. [ABSTRACT FROM AUTHOR]

Ocean warming and acidification may substantially affect the reproduction of keystone species such as Fucus vesiculosus (Phaeophyceae). In four consecutive benthic mesocosm experiments, we compared the reproductive biology and quantified the temporal development of Baltic Sea Fucus fertility under the single and combined impact of elevated seawater temperature and pCO2 (1100 ppm). In an additional experiment, we investigated the impact of temperature (0-25°C) on the maturation of North Sea F. vesiculosus receptacles. A marked seasonal reproductive cycle of F. vesiculosus became apparent in the course of 1 year. The first appearance of receptacles on vegetative apices and the further development of immature receptacles of F. vesiculosus in autumn were unaffected by warming or elevated pCO2. During winter, elevated pCO2 in both ambient and warmed temperatures increased the proportion of mature receptacles significantly. In spring, warming and, to a lesser extent, elevated pCO2 accelerated the maturation of receptacles and advanced the release of gametes by up to 2 weeks. Likewise, in the laboratory, maturation and gamete release were accelerated at 15-25°C relative to colder temperatures. In summary, elevated pCO2 and/or warming do not influence receptacle appearance in autumn, but do accelerate the maturation process during spring, resulting in earlier gamete release. Temperature and, to a much lesser extent, pCO2 affect the temporal development of Fucus fertility. Thus, rising temperatures will mainly shift or disturb the phenology of F. vesiculosus in spring and summer, which may alter and/or hamper its ecological functions in shallow coastal ecosystems of the Baltic Sea. [ABSTRACT FROM AUTHOR]

We present an annotated list of new finds of red algae from Hainan Island, Southern China, including those found in 1990 and 1992 during the German-Chinese expeditions to Hainan Island and in 2008-2016 by Titlyanova, Titlyanov, and Li. Between 1990 and 1992, a total of 64 taxa of red algae were newly recorded for Hainan Island. Of these 15 species were new records for China. During the period 2008-2016, a further 54 taxa were newly recorded for Hainan Island, of which 20 were new records for China. The full list of new taxa includes taxonomic forms, dates and locales, together with known biogeographical distributions. During both periods, the apparent enrichment of red algal marine flora has occurred in a similar way--mainly at the expense of epiphytes with filamentous, thin-filamentous, and finely branched forms. We believe that the changes in the flora of Hainan Island have been influenced by both anthropogenic and natural factors including in particular exploitation of herbivores, nutrient pollution and coral bleaching. [ABSTRACT FROM AUTHOR]

Kelp beds worldwide are under pressure from ongoing climate and environmental change. Along European coastlines increases in seawater temperature and changes in nutrient conditions occur where upwelling events are disrupted and also along eutrophicated coasts. In addition, seaweed responses to change may interact with seasonal daylength cycles. We performed a factorial experiment to examine the combined effects of seawater temperatures, nutrient regimes and photoperiod (long and short days) in order to better understand how latitudinal or seasonal differences in daylengths affect the sensitivity of transient microscopic kelp stages of Laminaria digitata from the North Sea to warming and eutrophication. While the optimal temperature range for vegetative gametophyte growth was 10°C-18°C under long summer photoperiod conditions, gametogenesis was induced at lower temperatures between 5°C and 15°C, with maximum sporophyte development under long photoperiods and enriched nutrient regimes, which represent local late spring conditions. Although gametogenesis was fastest at 10°C-15°C, sporophyte recruitment was highest at 5°C. As these particular early life cycle processes in L. digitata have different temperature optima, this may drive the seasonal cycle of recruitment in the field. Increasing summer temperatures due to global warming will increase gametophyte size due to enhanced vegetative growth and inhibition of gametogenesis. This will probably lead to delayed but enhanced recruitment of new sporophytes under cooler autumn to spring conditions over a wide geographical scale, preventing the formation of juvenile sporophytes under stressful summer conditions and possibly changing annual recruitment patterns. [ABSTRACT FROM AUTHOR]

In Arctic macroalgal belt ecosystems, macrozoobenthic production is thought to be an important link between primary production and higher trophic levels. Macrozoobenthic biomass and secondary production were studied along transects (2.5-15 m depth) in the macroalgal belt at Hansneset in Kongsfjorden, Svalbard, from 2012 to 2013. At 2.5 m, the standing stock reached its maxima of 174.8 ± 54.4 g ash-free dry weight per 1 m, while density (4341 ind. m ± 1127 95 % CI) and production (7.0 g C m y ± 2.8 95 % CI) were highest at 5 m water depth in 2012/13. Compared to a study from 1996/98, this re-sampling indicated a drastic change in the depth distribution of macrozoobenthic biomass and secondary production at Hansneset. While both biomass and secondary production increased with water depth in 1996/98, this pattern was inversed in 2012/13 owing to a tenfold increase in biomass and secondary production in the upper most sublittoral (2.5-5 m). Variability of macrozoobenthic biomass and secondary production corresponded to differences in the physical environment and macroalgal vegetation along the depth gradient. In the last decade, the number of ice-free days per year increased probably due to Arctic warming. As a result, shallow rocky habitats (2.5-5 m) are less affected by ice scouring, thereby opening new space for colonisation by benthic fauna. However, faunal secondary production was low compared to macroalgal primary production, indicating a considerable export of most of the algal production from the shallow habitats to the adjacent areas. [ABSTRACT FROM AUTHOR]

Seaweeds provide important ecosystem services in coastal areas, and loss of these macrophytes due to anthropogenic global change and warming is a worldwide concern. Fucus vesiculosus L. (Phaeophyceae) is the most abundant and hence ecologically most important primary producer, carbon sink and habitat provider in the western Baltic Sea. Therefore, we used this keystone species to test phenotypic acclimation of physiological performance traits (growth, photosynthesis and metabolites) of F . vesiculosus apices in a well-defined and highly resolved temperature gradient (5–29 °C), supported by highly temporally resolved measurements. Temperature requirements of growth and photosynthesis were evaluated in three weeks exposure experiments, and changing tolerance ranges for survival over time were determined. Fucus vesiculosus was able to grow and survive over a temperature range from 5 to 26 °C without any injury or visible damage of the apical growing meristem over all three weeks. However, at higher water temperatures (≥ 27 °C) growth rapidly decreased from day three onwards and progressive necrosis was observed at 28 and 29 °C. Stress-induced decrease in growth rate was already indicated by the effective quantum yield of chlorophyll fluorescence of photosystem II (PSII) several days in advance. Optimal temperature for photosynthesis (24 °C), measured as electron transport rate, was higher compared to that for growth (15–20 °C). Accordingly, the concentration of mannitol, the main product of photosynthesis, increased with higher temperatures. Understanding physiological responses of keystone macroalgae with respect to temperature and time is important, because rising global temperatures and summer heat wave frequencies and duration may affect the ecological functions of F . vesiculosus in the western Baltic Sea. [ABSTRACT FROM AUTHOR]

A methodology to classify rocky shores along the North East Atlantic (NEA) region was developed. Previously, biotypes and the variability of environmental conditions within these were recognized based on abiotic data. A biological validation was required in order to support the ecological meaning of the physical typologies obtained. A database of intertidal macroalgae species occurring in the coastal area between Norway and the South Iberian Peninsula was generated. Semi-quantitative abundance data of the most representative macroalgal taxa were collected in three levels: common, rare or absent. Ordination and classification multivariate analyses revealed a clear latitudinal gradient in the distribution of macroalgae species resulting in two distinct groups: one northern and one southern group, separated at the coast of Brittany (France). In general, the results based on biological data coincided with the results based on physical characteristics. The ecological meaning of the coastal waters classification at a broad scale shown in this work demonstrates that it can be valuable as a practical tool for conservation and management purposes. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the ecological implications of global climate change requires investigations of not only the direct effects of environmental change on species performance but also indirect effects that arise from altered species interactions. We performed CO2 perturbation experiments to investigate the effects of ocean acidification on the trophic interaction between the brown seaweed Fucus vesiculosus and the herbivorous isopod Idotea baltica. We predicted faster growth of F. vesiculosus at elevated CO2-concentrations and higher carbon content of the algal tissue. We expected that I. baltica has different consumption rates on algae that have been grown at different CO2 levels and that the isopods remove surplus carbon metabolically by enhanced respiration. Surprisingly, growth of F. vesiculosus as well as the C:N-ratio of the algal tissue were reduced at high CO2-levels. The changes in the elemental composition had no effect on the consumption rates and the respiration of the herbivores. An additional experiment showed that consumption of F. vesiculosus by the isopod Idotea emarginata was independent of ocean acidification and temperature. Our results could not reveal any effects of ocean acidification on the per capita strength of the trophic interaction between F. vesiculosus and its consumers. However, reduced growth of the algae at high CO2-concentrations might reduce the capability of the seaweed to compensate losses due to intense herbivory. [Copyright &y& Elsevier]

A complete checklist of intertidal to shallow subtidal marine green seaweeds (Chlorophyta) growing on the subtropical island of Hainan (China) is presented here for the first time. It covers data from extensive recent (1990-2009) and historical (1933-1935) collections, and additional published records from various time periods. Data were analyzed by time period. We postulate that environmental changes on Hainan Island documented since the 1980s (e.g., degradation of coral reefs, development of tourism and mariculture farms) are reflected in the green algal species complement and in the dominance or absence of specific algal groups during different time periods. In total, 105 green algal taxa were recorded, including 37 new to Hainan Island, and 18 new records for China. There was a clearly evident change in floristic composition between early and recent collections. In the 1930s, there was a dominance of Caulerpaceae, Codiaceae and Cladophoraceae. By 1990/1992, the numbers of Ulvaceae had increased 1.6-fold and numbers of Cladophoraceae 1.7-fold. Both families contain many opportunistic species that prefer nutrient-enriched or degraded environments. At the same time, species richness of Codiaceae, Caulerpaceae and Udotaceae, families with complex thallus structures, decreased considerably. The floristic differences between the 1990/1992 and 2008/2009 collections were minor. [ABSTRACT FROM AUTHOR]

The general aim of setting up a central database on benthos and plankton was to integrate long-, medium- and short-term datasets on marine biodiversity. Such a database makes it possible to analyse species assemblages and their changes on spatial and temporal scales across Europe. Data collation lasted from early 2007 until August 2008, during which 67 datasets were collected covering three divergent habitats (rocky shores, soft bottoms and the pelagic environment). The database contains a total of 4,525 distinct taxa, 17,117 unique sampling locations and over 45,500 collected samples, representing almost 542,000 distribution records. The database geographically covers the North Sea (221,452 distribution records), the North-East Atlantic (98,796 distribution records) and furthermore the Baltic Sea, the Arctic and the Mediterranean. Data from 1858 to 2008 are presented in the database, with the longest time-series from the Baltic Sea soft bottom benthos. Each delivered dataset was subjected to certain quality control procedures, especially on the level of taxonomy. The standardisation procedure enables pan-European analyses without the hazard of taxonomic artefacts resulting from different determination skills. A case study on rocky shore and pelagic data in different geographical regions shows a general overestimation of biodiversity when making use of data before quality control compared to the same estimations after quality control. These results prove that the contribution of a misspelled name or the use of an obsolete synonym is comparable to the introduction of a rare species, having adverse effects on further diversity calculations. The quality checked data source is now ready to test geographical and temporal hypotheses on a large scale. [ABSTRACT FROM AUTHOR]

Presents a reappraisal of Porphyra and Bangia in the northeast Atlantic ocean based on the rbcL-rbcS intergenic spacer. 11 distinct sequences of the rbcL-rbcS noncoding intergenic spaces of the plastic genome for 47 species; Comparison of sequence data; Possibility of alien species in the northeast Atlantic ocean.