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Chloroplast DNA is methylated in the kelpSaccharina japonica, in contrast to most plants. Its function is yet largely unexplored. We detected methylation in the chloroplast DNA of the congenerSaccharina latissima, a non-model macroalgal species of high ecological (wild populations) and economical (wild and cultured populations) importance in the North Atlantic. To the functional relevance of chloroplast DNA methylation, we compared for the first time methylation patterns between wild and cultured kelp from different climatic regions (High-Arctic (79 °N) and temperate (53 °N), laboratory samples at 5 °C, 10 °C and 15 °C). Our results suggest genome-wide differences in methylated sites, and methylation level, between the climatic regions. At gene level, our data found functions related to photosynthesis to be the predominant affected case only for differential methylation between origins, but not between growth conditions. Here, sample origin led to significant differences between cultivated and wild samples due to differential methylation of genes related to DNA replication in the Spitsbergen samples. Both findings indicate that origin and cultivation strongly affected the chloroplast methylome, but differently. Similar methylomes for samples from the same origin – independent from whether they grow in the wild or in the lab – suggest that origin-specific methylation marks on the chloroplast genome are inherited. However, the capacity for rapid adaptation (to cultivation conditions) could be shown forSaccharina latissimaduring this study. Given that DNA-methylation affects gene expression, our study suggests that lab-cultivation alters epigenetically determined kelp chloroplast characteristics at least to the same degree as ecotypic differentiation does.

The seaweed

Polar regions are facing rapid temperature increase. In Arctic fjord systems, increased temperatures result in hyposalinity caused by the melting of sea ice and glaciers and freshwater run-off. Additionally, enhanced freshwater discharge and intrusion of nutrient-rich Atlantic water may result in nutrient input in summer. Combined, these factors might have a strong impact on primary producers, such as the abundant kelp speciesSaccharina latissima, an important foundation species in Arctic shallow-water coastal ecosystems. We ran 2 short-term 2factor experiments with field samples from Kongsfjorden (Svalbard) to evaluate the impact of temperature increase in summer combined with hyposalinity (temperature × salinity) or nutrient enrichment (temperature × nutrients) on the physiological and biochemical status of ArcticS. latissima. In the temperature × salinity experiment, growth and maximum photosynthetic quantum yield of photosystem II (Fv/Fm) were generally not affected. Temperature increase resulted in increased C:N ratios, based on decreasing nitrogen assimilation. Overall, hyposalinity had no severe effect but resulted in lower phlorotannin concentrations. Growth andFv/Fmimproved with increasing temperatures and nutrient enrichment. The de-epoxidation state of the xanthophyll cycle and mannitol declined at higher temperatures. Regarding other biochemical response variables, nutrients had no major impact (temperature × nutrients). In conclusion, in line with its broad latitudinal distribution range and adaptability,S. latissimaproved to be highly resilient to changing abiotic drivers and will likely be promoted by warming in the future Arctic.

Geographic variation of phenotypic traits affects the capacity of species to withstand and adapt to environmental stress. Here, we examined how geographic origin influences UV stress tolerance of the red seaweeds Chondracanthus chamissoi and Gelidium lingulatum distributed along the South-East Pacific coast between 20° S and 42° S. Seaweeds from six (C. chamissoi) and five (G. lingulatum) populations were grown under common-garden conditions and then exposed to consecutive UV stress events and essential biological traits (e.g., growth, photosynthetic responses, antioxidant capacity, and UV-absorbing compounds) were analyzed. In C. chamissoi, a strong UV sensitivity occurred in populations from mid-latitudes (27° S and 29° S) where the lowest recovery of maximum quantum yield (Fv /Fm ; between 32.3% and 66.8% of control) and growth rate were observed. Likewise, the lowest amount of mycosporine-like amino acids (MAAs) and a significant decrease in phycobilins were registered in these populations. In G. lingulatum, recovery of Fv /Fm ranged from 82.0% to 97.7% of control, and antioxidant activity, carotenoid, and MAA contents were positively influenced by UV exposure. The multivariate analysis indicated a significant influence of PAR, cloud cover, and UV index on physiological traits, depending on species. The ecotypic differentiation index (EDI) indicated a higher phenotypic variation in C. chamissoi (EDI = 0.10) than G. lingulatum (EDI = 0.03). This study shows that the spatial distribution of UV stress tolerance in the studied seaweeds does not follow linear latitudinal or central-edge gradients. Instead, among-site variability of solar intensities driven by specific climatic conditions seems to act as driver of phenotypic variation.

Macroalgae such as kelp are important ecosystem engineers in the Polar Regions and potentially affected by freshening and ocean warming. The endemic Arctic kelp Laminaria solidungula might be particularly imperiled and become locally extinct from Arctic fjord systems in the future, since temperature increase is most pronounced in the Polar Regions. Additionally, increased temperatures cause glacier and sea ice melting and enhancing terrestrial run-off from snowfields, which eventually can result in hyposaline conditions in fjord systems. We conducted a multiple-stressor experiment at four temperatures (0, 5, 10, 15 °C) and two salinities (SA 25, 35) to investigate the combined effects of increasing temperature and decreasing salinities on the physiological and biochemical status of young L. solidungula sporophytes. Both drivers had significant and interacting impacts, either in an additive or antagonistic way, dependent on the respective response variable. The maximum quantum yield of photosystem II (Fv/Fm) significantly declined with temperature increase and low salinity. Even though the absolute pigment content was not affected, the deepoxydation state of the xanthophyll cycle increased with intensified stress. Higher temperatures affected the C:N ratio significantly, mainly due to reduced nitrogen uptake, while SA 25 supported the nitrogen uptake, resulting in an attenuation of the effect. The concentration of mannitol decreased at SA 25. At control SA 35 mannitol level remained steady between 0 and 10 °C but significantly decreased at 15 °C. Conclusively, our results show that L. solidungula is very susceptible to both drivers of climate change, especially when they are combined. Implications to species ecology are discussed.

The underwater light regime is fundamental to the ecological health of aquatic systems because it is a limiting factor for photosynthesis in marine plants such as seagrasses. Although seagrass meadows are a key component of coastal systems, their survival has been threatened by increased turbidity levels, both from resuspension of marine sediments and input of terrestrial material. The objective of this study was to investigate how marine (typically grey/white in colour) and terrestrial (typically more yellow-orange in colour with finer texture) sediments affect underwater light quality. Two experimental systems were used: (1) a large outdoor tank and (2) laboratory controlled small sampling container, using natural terrestrial and marine sediment samples (with different colours and grain sizes) from New Zealand. In the tank experiments, high concentrations of sediment reduced transmittance considerably, particularly below 450 nm. Since seagrasses absorb light optimally at wavelengths

Abstract Correlative species distribution modelling is a widely used method to predict potential species ranges but can suffer from limitations in integrating species’ fundamental niches. Therefore, they might underestimate suitable ranges, but including physiological information can improve accuracy of predictions and help identify mechanisms of e.g. range limitation. However, approaches using both, results from correlative as well as physiological investigations are rare, especially in research on seaweeds. Here, we provide results from both approaches to predict the suitable habitat range of Capreolia implexa (Rhodophyta) in its native range (Australia and New Zealand) and invaded range (Chile) under present and future climate scenarios (year 2100, rcp 2.6 and rcp 8.5). We used the Maxent modelling technique and physiological knowledge from a temperature tolerance experiment (2–20 °C) for thermal niche estimation. Results from both approaches suggest larger suitable habitat ranges under present day conditions for both regions than currently occupied. Abiotic range limitation in the native range led to underestimation of the suitable temperature range by Maxent (here lower temperature limit = 8.3 °C). Predictions based on the laboratory temperature tolerance experiment suggest additional suitable habitat in colder regions (here lower temperature limit = 6.6 ± 0.4 °C). Under future climate conditions, both native and invaded ranges should shift southward, which will lead to an overall loss of suitable habitat in the native range. Like that, rcp 8.5 conditions should reduce the native range to 50% of the present-day extent. We demonstrate the limitation of correlative SDM modelling for species that live on continental margins and that physiological experiments can help to identify species’ niches beyond correlative analyses, providing valuable information for range projections. Furthermore, we provide valuable insights relevant for both invasion management and conservation. Graphic abstract

Previous field studies in the Southern Ocean (SO) indicated an increased occurrence and dominance of cryptophytes over diatoms due to climate change. To gain a better mechanistic understanding of how the two ecologically important SO phytoplankton groups cope with ocean acidification (OA) and iron (Fe) availability, we chose two common representatives of Antarctic waters, the cryptophyte Geminigera cryophila and the diatom Pseudo-nitzschia subcurvata. Both species were grown at 2°C under different pCO

Natural stony and coarse-grained habitats entail important ecological features for the marine environment. Due to the complexity of their bottom characteristics, they host a high biodiversity compared to surrounding soft bottom areas. The German nature conservation area “Helgolander Steingrund” (HSG; 54°14.00 N and 8°03.00 W) is subject to regular monitoring but lacks information on the spatial distribution of benthic species. Within this study, a new approach using species distribution models (SDM) was tested to fill these gaps of knowledge. Newly recorded environmental data (depth, sediments, current velocities) in the HSG and information on the presence and absences of nine benthic species (Echinus esculentus, Metridium senile, Cancer pagurus, Phymatolithon spp., Axinella polypoides, Homarus gammarus, Flustra foliacea, Alcyonidium diaphanum, Alcyonium digitatum), collected using video analysis of drop camera records, was used to perform SDMs. The models revealed good evaluation measures (true skill statistic > 0.7; area under the receiver operation characteristic curve > 0.90), implying that the model showed good predictive performance for the potential distribution of the tested species. The outcome of this study is a clear recommendation on SDM application in further environmental monitoring programs on the HSG and other protected hard ground areas.

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.

Benthic plants such as seagrasses rely on light availability, which is controlled by light attenuation in the water column. Elevated suspended sediment within estuaries strongly influences light attenuation and is governed by the recent history of natural events and human activities. To determine the constituents controlling light penetration (quantified by the irradiance attenuation coefficient, Kd(PAR)), we measured irradiance profiles, suspended particulate matter, chlorophyll-a and coloured dissolved organic matter (CDOM) in a barrier-enclosed estuary in New Zealand, subjected to dredging activity. These discrete measurements were then used to relate a continuous records of turbidity to potential light availability at multiple sites within the estuary. To do this, we use a regression model to enable turbidity measurements to be used as a proxy to estimate Kd(PAR). Measured Kd(PAR) ranged from 0.16 m-1 to 0.98 m-1 with overall average of 0.40 m-1, while Kd(PAR) inferred from continuous turbidity (which included many more events) reached higher values with average of 0.63 m-1. Continuous measurements of turbidity taken around the harbour dredging sites during dredging were slightly higher at some sites and slightly lower at others (∼2 mg l−1) compared to background measurements, indicating dredging had no consistent effect on conditions. Variations in Kd(PAR) were explained mostly by suspended particulate matter (accounting for 38%–50% of variance), chlorophyll-a (explaining 25%–33%) and to a lesser extent by coloured dissolved organic matter (CDOM explaining 10%–28%). Inferred benthic light availability in the intertidal zone when immersed ranged from 28% to 76% of surface irradiance, suggesting that light availability in the intertidal zone is not limiting seagrass photosynthesis but that growth in subtidal areas such as channels may be impacted. Results, inferred from continuous turbidity measurements, demonstrate the critical importance of including storm events in monitoring to develop robust limits on light attenuation for management.

Undaria pinnatifida, a kelp species native to East Asia, has become cosmopolitan and drawn increasing attention due to its worldwide spread in recent decades. Floating fragments of this alga were f...

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., We aimed to understand the intraspecific thermal variation of a coastal foundation species, the kelp Laminaria digitata. Marginal populations in particular differed in their response to heat stress treatments, while multilocus genotypes showed a clear and broad separation of L. digitata populations into a “northern” and a “southern” clade. These results imply that L. digitata populations have phenotypically diverged under the influence of the Quaternary glacial cycles.

The kelp Undaria pinnatifida, native to East Asian shores, was unintentionally introduced with Pacific oysters into the Mediterranean in 1971. Intentional introduction from there to the French Atlantic coast 12 years later led to a gradual spread to the British Isles and the North Sea. Here, we report on the northernmost established population in continental Europe, and suggest a further spread into Scandinavian waters to be almost inevitable. In 2016, several thalli were found washed ashore at the eastern side of the island of Sylt in the northern Wadden Sea (German Bight, Eastern North Sea). Most specimens bore fertile sporophylls and thallus lengths of >1 m were common. In June 2017, 91 sporophytes were found attached to a mixed bed of Pacific oysters and native blue mussels, located just below low tide level in a moderately sheltered position. Mean thallus length was 0.2 m and the longest 0.7 m. Most had distinctive sporophylls and released spores in the laboratory. From sporophylls collected in the previous year, we successfully reared a new generation, demonstrating the kelp’s potential for further spread by natural means or human vectors.

Impacts of rising atmospheric CO 2 concentrations and increased daily irradiances from enhanced surface water stratification on phytoplankton physiology in the coastal Southern Ocean remain still unclear. Therefore, in the two Antarctic diatoms Fragilariopsis curta and Odontella weissflogii, the effects of moderate and high natural solar radiation combined with either ambient or future pCO 2 on cellular particulate organic carbon (POC) contents and photophysiology were investigated. Results showed that increasing CO 2 concentrations had greater impacts on diatom physiology than exposure to increasing solar radiation. Irrespective of the applied solar radiation regime, cellular POC quotas increased with future pCO 2 in both diatoms. Lowered maximum quantum yields of photochemistry in PSII (Fv/Fm) indicated a higher photosensitivity under these conditions, being counteracted by increased cellular concentrations of functional photosynthetic reaction centers. Overall, our results suggest that both bloom‐forming Antarctic coastal diatoms might increase carbon contents under future pCO 2 conditions despite reduced physiological fitness. This indicates a higher potential for primary productivity by the two diatom species with important implications for the CO 2 sequestration potential of diatom communities in the future coastal Southern Ocean.

The kelp Alaria esculenta represents a key species in high Arctic marine fjord ecosystems. However, the European Arctic is currently experiencing extensive environmental change. Glacial fjord systems, such as Kongsfjorden (Spitsbergen, Svalbard), are subjected to rising temperature, increased freshwater inflow from glaciers and melting snow and a changing ultraviolet (UV) radiation regime related to stratospheric ozone depletion. Thus, in addition to natural seasonality, sessile organisms require acclimation in order to adapt to an environment in transition. We examined the physiological and ultrastructural responses of A. esculenta to the combined exposure to hyposalinity and UV radiation. Photosynthetic quantum yield slightly decreased during a low-salinity treatment of 7 d. Exposure to UV radiation also lowered quantum yield, but specimens previously treated with hyposalinity were significantly less susceptible to UV than nontreated individuals. Concomitant with a loss of chlorophyll during t...

Overland transport in open-air-exposed conditions, including the translocation of specimens fouled on trailered boat hulls, aquaculture ropes or entangled in fishing gear, is recognized as a short-distance vector for the introduction of invasive aquatic species. Here, the desiccation tolerance for different life stages of the invasive kelp Undaria pinnatifida was determined to test the likelihood of air-exposed transport. Water content, photosynthetic quantum yield (Fv/Fm) as well as the capacity to release viable spores were monitored for mature sporophylls during a five-day exposure to air conditions. For newly settled spores (16 h post-release) and developing gametophytes (30 h post-release) survival and growth were observed after 1, 3, 6, 12 and 24 h of desiccation. Additionally, spore settlement and desiccation survival (after 3, 12 and 48 h) were determined for seven-day-old gametophytes growing on different rope materials (hemp, polypropylene, polyethylene, nylon) in high (99% relative air humidity, RH) and typical (59% RH) air humidity conditions. Viable spores were released from mature sporophylls after three days of desiccation. U. pinnatifida. This is a vector that should be considered for pest management.

Macrocystis pyrifera (L.) C. Agardh is a species that forms extensive underwater forests along the coastline of the ecoregion of Magellan. There, this alga is exposed to marked variation in photoperiod, temperature, and irradiance, which are modulated by daily and seasonal climatic variations. This study aims to understand the ecophysiological behavior of M. pyrifera, in a natural forest localized in Puerto del Hambre, Magellan Region of Chile, along spatial (depth) and temporal (season) gradients of physical drivers by analyzing algal responses in terms of the photosynthetic pigments and fluorescence yield. In the apical, middle, and basal fronds, the following photosynthetic parameters were seasonally measured: electron transport efficiency (α), maximum relative rate of electron transport (rETRmax), saturation point (E k ), and pigments such as chlorophyll a (Chl a), chlorophyll c (Chl c), and fucoxanthin. Both seasonal and stratified variations were observed. In autumn, α was decreased in the middle fronds (0.136 ± 0.030 (μmol photons m−2 s−1)−1) with respect to apical and basal fronds of autumn. For parameters such as E k , this decrease was observed relative to the depth gradient, with significant differences (p

Ecophysiological studies on Antarctic cryptophytes to assess whether climatic changes such as ocean acidification and enhanced stratification affect their growth in Antarctic coastal waters in the future are lacking so far. This is the first study that investigated the combined effects of increasing availability of pCO2 (400 and 1000 µatm) and irradiance (20, 200 and 500 μmol photons m−2 s−1) on growth, elemental composition and photophysiology of the Antarctic cryptophyte Geminigera cryophila. Under ambient pCO2, this species was characterized by a pronounced sensitivity to increasing irradiance with complete growth inhibition at the highest light intensity. Interestingly, when grown under high pCO2 this negative light effect vanished and it reached highest rates of growth and particulate organic carbon production at the highest irradiance compared to the other tested experimental conditions. Our results for G. cryophila reveal beneficial effects of ocean acidification in conjunction with enhanced irradiance on growth and photosynthesis. Hence, cryptophytes such as G. cryophila may be potential winners of climate change, potentially thriving better in more stratified and acidic coastal waters and contributing in higher abundance to future phytoplankton assemblages of coastal Antarctic waters.

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.

This book summarizes physical and biological aspects from Kongsfjorden (78° 59’ N, 11–12° E), Svalbard. The contributions to this volume cover atmospheric conditions above Ny-Alesund, as well as physical conditions in Kongsfjorden. The chapters about oceanographic dynamics and sea ice conditions are based on time-series observations of interannual variability, whereas the chapter about the underwater light regime focuses on seasonal dynamics. The pelagic system is covered by reviews of pelagic production, phytoplankton and zooplankton communities. Benthic flora studies address microphytobenthos and macroalgal biodiversity, as well as the physiology of kelp related to stress perception and responses. Benthic fauna communities are described with associated environmental drivers of change. An outline of an Arctic fjord ecosystem model for Kongsfjorden- Krossfjorden is presented. Data that go into models come from sampling at different stations in the marine environment, with an important contribution from long-term data series at stations. Some of the long-term data are based on recordings from autonomous underwater observatories. Finally, one summary presents Kongsfjorden as harbinger of the future Arctic.

On rocky substrata along shallow water cold-temperate and Arctic coastlines, large brown seaweeds (“kelps”) form structure- and organism-rich habitats of vast ecological significance. The distribution of these ecosystem engineers is largely controlled by the prevailing temperature, light regime and substrate availability, but can also be influenced by biotic interactions within the kelp communities. In Kongsfjorden, right in the transition of an Arctic to an Atlantic fjord system, the aforementioned factors are likely to be altered as a consequence of regional and global environmental change. The drivers of change entail increasing surface irradiances of harmful ultraviolet B radiation due to stratospheric ozone depletion, and variations related to increased atmospheric carbon dioxide concentrations, such as increase in atmospheric and sea surface temperatures with their marked influence on sea ice formation and ocean acidification. Other factors potentially driving the Kongsfjorden system into change might be alterations of current and wind patterns resulting in the increased inflow of Atlantic waters into the bay (Atlantification), and increased precipitation, and terrestrial and glacial runoff, yielding an altered salinity regime and sediment discharge into the fjord with the potential impact of reducing light availability to marine photosynthesizers. Hence, this article is aiming to provide an overview on ecologically relevant abiotic and biotic factors influencing kelp distribution, and with the potential to eventually act as environmental stressors. We assess responses on different organisational levels of kelp by following the effects cascading from the initial sensing of the environment, signal transduction to gene expression, physiological reactions, changes in cellular ultrastructure and subsequent consequences for growth, reproduction and population biology for the different species of kelps present in Kongsfjorden.

Ultraviolet (UV) radiation is a significant stress factor that harms life in both terrestrial and aquatic ecosystems in Antarctica. In summer (January–February), ground-level solar radiation regimes at the Antarctic Carlini Station (62°14'S, 58°40'W) on King George Island (South Shetland Islands) can be highly variable, depending on the presence of clouds. Spectrally-resolved underwater radiation regimes were measured at three study sites in the inner and outer Potter Cove nearby Carlini Station. The clear waters at Penon de Pesca allowed PAR, UV-A and UV-B radiation to penetrate deeply into the water column, expressed by z1% (i. e. 1%-depths) at 23–25 m, 20–22 m and 13–16 m, respectively, as well as by low attenuation coefficients of downward radiation (Kd). In contrast, turbid waters in the inner Potter Cove and at Penon Uno reduced the penetration of these three wavebands significantly. The photo-physiological mechanisms allowing macroalgae to acclimate to the incident gradients of PAR and UV radiation at Penon de Pesca were further elaborated by assessing photo-physiological data on the brown macroalga Desmarestia menziesii (Phaeophyceae), exposed to a PAR range between 15 and 130 μ mol photons m-2 s-1, either in the presence or absence of UV radiation (10.3 W m -2 UV-A and 0.73 W m -2 UV-B). PAM-fluorometry-based measurements revealed a similar decrease of the optimum quantum yield of photosystem II (PSII) under both PAR and UV radiation and a stronger effect of PAR over UV radiation in the regulation of maximum photosynthetic electron transport rate (ETRmax) as well as the photosynthetic light saturation (Ek). The down-regulation of the photochemistry of PSII by PAR as well as the reduction in the photosynthetic electron transport capacity (i.e.ETRmax) indicate important photoprotective mechanisms allowing D. menziesii to response effectively to a combination of PAR and UV stress in their upper subtidal habitat.

Light adaptive strategies were studied in a comparative analysis of the congeneric seagrass species Zostera muelleri and Zostera marina at two case study areas in New Zealand and Germany. Surveys in intertidal seagrass meadows were conducted from pre-dawn until sunset on days when either low or high tide coincided with noon. The results show marked fluctuations of photophysiology (optimum and effective quantum yield, non-photochemical quenching, cycling of xanthophyll cycle (XC) pigments) over daily and tidal cycles. At both locations, we observed a near complete conversion (de-epoxidation) of violaxanthin to zeaxanthin at times with high irradiance and a rapid and complete re-epoxidation under subsequent lower light conditions. At the New Zealand site we also observed significantly larger XC-pigment pool sizes in seagrass leaves sampled in a week when low tide coincided with noon (larger daily fluence and higher maximum irradiance), compared with leaves sampled in a week when high tide was at noon. This dynamic adjustment of xanthophyll pool size has not been previously reported for intertidal seagrasses. It adds to our understanding of an important adaptive feature in a highly dynamic light environment and to the general ecology and adaptability of seagrasses.

Seasonal environmental changes may significantly influence macroalgal diversity and biomass. Cryptogam species richness increases towards the poles, especially in sub-Antarctic environments. Yet, subpolar seaweed biodiversity and ecophysiology remain understudied even though it is essential for the management and sustainability of endemic species of significant economic interest (e.g., Gigartina skottsbergii). We evaluate the seasonality and ecophysiology of the different life phases of the rhodophyte G. skottsbergii by analyzing variation in fluorescence yield and photosynthetic pigment composition. There were significant seasonal differences in maximum relative electron transport rate (rETRmax) between gametophyte and tetrasporophyte phase, and between reproductive and vegetative specimens. Photosynthetic efficiency (α) was not significantly different between reproductive states of G. skottsbergii. We found significant differences in mean concentrations of allophycocyanin (APC), phycocyanin (PC), and chlorophyll a (Chl a) between gametophyte and tetrasporophyte phases. Results obtained provide new insight into seasonal acclimation patterns of an ecologically important species, which can be used for the design of appropriate management and cultivation strategies of G. skottsbergii towards the restoration of natural populations in fragile, subpolar regions where some of the last, relatively undisturbed communities of G. skottsbergii still remain.

Concrete is used in marine coastal constructions worldwide. These structures are colonized by specialized hard-bottom biota consisting of macroalgae and benthic macrofauna. As concrete manufacturers face challenges such as limited natural resources and high CO2-emissions, the need for supplementary materials increases. Still, there has been little research on the reaction of species to the differences in concrete composition and what ecological impact these reactions could have. This study addresses the questions (1) if there are differences in settlement communities, depending on differences in concrete constitutes and (2) if so, what are the consequences for the usability of alternative concretes in marine constructions. For the experiment 15 cubes (15 × 15 × 15 cm) made of five different concretes, containing different cements (Portland cement and blast furnace cements) and aggregates (sand, gravel, iron ore and metallurgical slags) were deployed in a natural hard bottom experimental field near Helgoland Island (German Bight) in April 2016. After 12 months, all cubes were examined regarding species composition and coverage, followed by statistical analysis (PERMANOVA, SIMPER, DIVERSE). Results indicate differences in settlement communities for different surface orientation (Top, Front/Back) of the cubes. Significant differences in settlement communities of the Front/Back side were present depending on the used material type. However, the found differences in settlement between the concrete types tested are not sufficiently clear to provide recommendations for their usability in coastal constructions.

Tissue nutrient concentrations are a key factor in determining primary production in a variety of algae, for example the marine macroalga Ulva. We present a novel algebraic solution to calculate the equilibrium tissue nitrogen concentration or “quota” Q. The solution is derived from a classical mechanistic description of “luxury uptake” in marine macroalgae using a computer algebra system. Forced by ammonium ( NH 4 + ) and nitrate plus nitrite ( NO x − ) concentrations, water temperature and irradiance, equilibrium Q can be calculated directly without the need for numerical integration, and the model performs well in reproducing observations of Q in frondose Ulva spp. A Sobol’ global sensitivity analysis reveals that the degree of uncertainty in physiological parameters has a similar magnitude of influence on model output as the typical environmental range of nutrient forcing data. The environmental forcing variables NH 4 + and NO x − together account for 60% of variance in model output, while the two most influential physiological parameters together account for another 32% of variance. Repeated parameter calibrations with random first guesses and evolutionary adaptations lead to broad and even multimodal distributions for some parameters, as well as values at the extremes of their literature ranges. This shows that although model performance as quantified by statistical measures is high, individual calibrations are not sufficient to give reliable parameter estimates that can be interpreted as physiological system properties.

Lessonia nigrescens used to be an abundant kelp species along the Chilean coast, but recent molecular studies revealed the existence of a L. nigrescens species complex, which includes the two cryptic species Lessonia berteroana and Lessonia spicata. Since these species have different distributions (16°S–30°S for L. berteroana and 29°S–42°S for L. spicata), they experience differences in environmental conditions, such as solar irradiance, seawater temperature and air exposure during low tide. This study tested to what extent the genetic distinctness of each of the two species [identified by a mitochondrial marker (atp8/trnS)] is reflected by ecophysiological traits (total lipids, fatty acid composition, phlorotannins, pigments and variable chlorophyll a fluorescence of PSII) in response to the respective environmental conditions, prevailing along the latitudinal gradient. We studied algal individuals from eight populations (27°S–32°S, including the species overlapping zone). Phlorotannins, pigments and Chl a fluorescence of PSII were most crucial for species-specific adaptations at the respective growth sites, whereas changes in total lipids and fatty acid compositions were negligible. Hence, species differentiation within the L. nigrescens complex is also manifested at the ecophysiological level. These findings may help to predict kelp responses towards future environmental changes.

Large brown seaweeds (kelps) represent ecologically important habitats in coastal systems. Along the western shores of the Svalbard archipelago, the kelp Alaria esculenta forms dense stands and provides habitat to a multitude of associated organisms. At the growth site in shallow waters, kelp sporophytes can be exposed to high irradiances of harmful ultraviolet (UV-B) radiation resulting from a thinning of the stratospheric ozone layer over the Arctic. Here, we tested to what extent UV-B-induced impairment of photophysiology is accompanied by changes in the cellular ultrastructure of A. esculenta and characterizes sites of cellular damage after UV exposure. Adverse effects on cellular components mostly manifest in chloroplast thylakoid membrane integrity, which is accompanied by a decrease in maximal quantum yield of photosystem II. At the applied irradiances of UV radiation, A. esculenta is stressed to an intermediate extent confirming its adaptability to a moderately increased UV-B climate.

Ocean acidification studies in the past decade have greatly improved our knowledge of how calcifying organisms respond to increased surface ocean CO2 levels. It has become evident that, for many organisms, nutrient availability is an important factor that influences their physiological responses and competitive interactions with other species. Therefore, we tested how simulated ocean acidification and eutrophication (nitrate and phosphate enrichment) interact to affect the physiology and ecology of a calcifying chlorophyte macroalga (Halimeda opuntia (L.) J.V. Lamouroux) and its common noncalcifying epiphyte (Dictyota sp.) in a 4-week fully crossed multifactorial experiment. Inorganic nutrient enrichment (+NP) had a strong influence on all responses measured with the exception of net calcification. Elevated CO2 alone significantly decreased electron transport rates of the photosynthetic apparatus and resulted in phosphorus limitation in both species, but had no effect on oxygen production or respiration. The combination of CO2 and +NP significantly increased electron transport rates in both species. While +NP alone stimulated H. opuntia growth rates, Dictyota growth was significantly stimulated by nutrient enrichment only at elevated CO2, which led to the highest biomass ratios of Dictyota to Halimeda. Our results suggest that inorganic nutrient enrichment alone stimulates several aspects of H. opuntia physiology, but nutrient enrichment at a CO2 concentration predicted for the end of the century benefits Dictyota sp. and hinders its calcifying basibiont H. opuntia.

We evaluated spatial differences in seagrass cover related to environmental conditions (light, temperature, sediment grain size distribution, and porewater nutrients) and differences in seagrass photosynthetic pigment composition and morphometry (above and below ground biomass, shoot length and leaf width, and percentage cover) at four sites in the meso-tidal estuarine lagoon Tauranga Harbour, North Island, New Zealand. Two sites were sandy and wave-exposed and two others were muddy and sheltered, while one of each site types was located in the north and south of Tauranga Harbour, respectively. Results showed marked differences in environmental conditions, seagrass metrics as well as in pigment content and composition. In particular, the sheltered site in the north was found to be different from the other sites, having the lowest light regime and highest mud and phosphate content. Seagrass at this site had the highest overall biomass, with especially high above ground biomass as well as elevated overall pigment content and both light harvesting and protective pigments. The exposed site in the north had the highest light levels and the lowest porewater ammonium content, accommodating intermediate seagrass biomass and low pigment contents. The two sites in the south had intermediate environmental conditions (except for the sheltered site, which had the highest porewater ammonium content), but lower seagrass biomass than the sites in the north. Our findings indicate that Zostera muelleri shows a high physiological and morphological plasticity and can grow in a wide range of environmental conditions. Intermediate light conditions, high mud content and phosphate content seem to benefit seagrass growth.

The endemic Antarctic brown macroalga Desmarestia anceps colonizes the subtidal between 5 and 30 m in Potter Cove on King George Island (South Shetland Islands, Antarctica). Experiments were conducted to study photosynthetic activities, antioxidative enzymes and UV tolerance of field-grown individuals with respect to the light histories along different subtidal positions. Individuals collected from the upper (5.5 m) and mid-subtidal (9.0 m) are characterized by high maximum electron transport rates (ETRmax) measured by PAM-fluorometry and high activities of superoxide dismutase (SOD) supported by considerable activities of glutathione reductase. Individuals of this species from the upper subtidal are able to tolerate high irradiances of UV-B radiation because its photosynthetic apparatus is putatively well protected by phlorotannins. In contrast, individuals from lower subtidal positions (13.5 and 15.5 m) showed an opposite trend: lower ETRmax and SOD activities as well as a lower UV tolerance of photosynthesis. Moreover, a non-denaturing polyacrylamide gel electrophoresis (native PAGE) of a partially purified crude extract reveals that D. anceps has probably six isoforms of SOD. These intra-specific patterns imply a high phenotypical plasticity of D. anceps with respect to its photosynthesis and photoprotective mechanisms. Overall, photosynthesis, UV tolerance and antioxidative potential are highly regulated in D. anceps corresponding to the respective light regimes along its natural growth sites.

Ocean acidification reduces the concentration of carbonate ions and increases those of bicarbonate ions in seawater compared with the present oceanic conditions. This altered composition of inorganic carbon species may, by interacting with ultraviolet radiation (UVR), affect the physiology of macroalgal species. However, very little is known about how calcareous algae respond to UVR and ocean acidification. Therefore, we conducted an experiment to determine the effects of UVR and ocean acidification on the calcified rhodophyte Corallina officinalis using CO2-enriched cultures with and without UVR exposure. Low pH increased the relative electron transport rates (rETR) but decreased the CaCO3 content and had a miniscule effect on growth. However, UVA (4.25 W m-2) and a moderate level of UVB (0.5 W m-2) increased the rETR and growth rates in C. officinalis, and there was a significant interactive effect of pH and UVR on UVR-absorbing compound concentrations. Thus, at low irradiance, pH and UVR interact in a way that affects the multiple physiological responses of C. officinalis differently. In particular, changes in the skeletal content induced by low pH may affect how C. officinalis absorbs and uses light. Therefore, the light quality used in ocean acidification experiments will affect the predictions of how calcified macroalgae will respond to elevated CO2.

Calcifying green macroalgae of the genus Halimeda are widely distributed on coral reefs and may become more abundant under higher nutrient availability. To determine how nutrient enrichment affects the physiological performance of Halimeda opuntia (Linnaeus) J.V.Lamouroux in relation to different water depths, we carried out in situ nutrient enrichment experiments in Curacao, Netherlands Antilles. H. opuntia was collected in 5 m and then incubated at 5 and 15 m in clear acrylic cages with or without addition of N and P. Growth, algal tissue composition (internal C, N, and P content, δ 15 N signatures, protein content), photosynthetic performance and pigment content were measured after 14 days of incubation. Growth rates and total C increased with nutrients and were higher in 5 m water depth. N and P content were higher and δ 15 N signatures were lighter with nutrients in both depths. Photosynthetic performance, concentrations of the main and accessory photosynthetic pigments, and photoprotection also increased with nutrients and showed some response to depth. These results indicate that nutrient enrichment supported a rapid increase in physiological performance of H. opuntia , but with differences in depth. In 5 m, more C was allocated to growth, where light levels were sufficient, while in 15 m C was allocated to photosynthetic pigments. These results suggest that nutrient enrichment may influence their abundance and depth distribution on the reef.

Grosalgen sind bedeutende Okosystemingenieure, die vielen assoziierten Tieren als Lebensraum, aber auch als Nahrung dienen. Diese fundamentalen Beitrage von Grosalgen zu den Okosystemfunktionen konnen in ihrer Bedeutung je nach Standort variieren. Exzessives Wachstum von Grosalgen durch Nahrstoffeintrage oder die Uberfischung von Weidegangern kann ein schwerwiegendes okologisches Problem darstellen, wenn Korallenriffe uberwuchert werden oder der bakterielle Abbau der Algenbiomasse zu Sauerstoffarmut fuhrt. In diesem Kapitel werden die Funktionsweise, die Bedeutung, aber auch die Gefahrdung von Grosalgengemeinschaften beleuchtet.

It is largely unknown how rising atmospheric COconcentrations and changes in the upper mixed layer depth, with its subsequent effects on light availability will affect phytoplankton physiology in the Southern Ocean. Linking seasonal variations in the availability of CO2 and light to abundances and physiological traits of key phytoplankton species could aid to understand their abilities to acclimate to predicted future climatic conditions. To investigate the combined effects of CO2 and light on two ecologically relevant Antarctic diatoms (Fragilariopsis curta and Odontella weisflogii) a matrix of three light intensities (LL = 20, ML = 200, HL = 500 µmol photons m-2 s−1) and three pCO2 levels (low = 180, ambient = 380, high = 1000 µatm) was applied assessing their effects on growth, particulate organic carbon (POC) fixation and photophysiology. Under ambient pCO2, POC production rates were highest already at low light in Fragilariopsis, indicating saturation of photosynthesis, while in Odontella highest rates were only reached at medium irradiances. In both species ocean acidification did not stimulate, but rather inhibited, growth and POC production under low and medium light. This effect was, however, amended under high growth irradiances. Low pCO2 levels inhibited growth and POC production in both species at low and medium light, and further decreased absolute electron transport rates under high light. Our results suggest that Southern Ocean diatoms were sensitive to changes in pCO2, showing species-specific responses, which were further modulated by light intensity. The two diatom species represent distinct ecotypes and revealed discrete physiological traits that matched their seasonal occurrence with the related physical conditions in Antarctic coastal waters.

To better understand the impact of ocean acidification (OA) and changes in light availability on Southern Ocean phytoplankton physiology, we investigated the effects of pCO2 (380 and 800 µatm) in combination with low and high irradiance (20 or 50 and 200 µmol photons m-2 s-1) on growth, particulate organic carbon (POC) fixation and photophysiology in the three ecologically relevant species Chaetoceros debilis, Fragilariopsis kerguelensis and Phaeocystis antarctica. Irrespective of the light scenario, neither growth nor POC cell-1 was stimulated by OA in any of the tested species and the two diatoms even displayed negative responses in growth (e.g. C. debilis) or POC content (e.g. F. kerguelensis) under OA in conjunction with high light. For both diatoms, also maximum quantum yields of PSII (Fv/Fm) were decreased under these conditions, indicating lowered photochemical efficiencies. To counteract the negative effects by OA and high light, the two diatoms showed diverging photoacclimation strategies. While cellular chlorophyll a and fucoxanthin contents were enhanced in C. debilis to potentially maximize light absorption, F. kerguelensis exhibited reduced chlorophyll a cell-1, increased disconnection of antennae from photosystem II reaction centers and strongly lowered absolute electron transport rates (ETR). The decline in ETRs in F. kerguelensis might be explained in terms of different species-specific strategies for tuning the available flux of adenosine triphosphate and nicotinamide adenine dinucleotide phosphate. Overall, our results revealed that P. antarctica was more tolerant to OA and changes in irradiance than the two diatoms, which may have important implications for biogeochemical cycling.

Invasive species are generally believed to be more tolerant to varying abiotic conditions than native species. Here, we report the combined effect of temperature (5, 15, 20 and 25 °C) and salinity (33, 24, 18, 12 and 6 SA) on the performance of the invasive kelp Undaria pinnatifida and two native kelp species (Lessonia variegata, Ecklonia radiata) from Tauranga Harbour, New Zealand (37°38′S, 176°10′E, 2014). Vegetative blade discs were exposed to temperature and salinity treatments in a 10-day laboratory experiment, and the physiological response was assessed employing photosynthetic (Fv/Fm, ETRmax) as well as biochemical parameters (chlorophyll a, xanthophylls and antioxidant pool size). U. pinnatifida sustained a high photosynthetic quantum yield in most treatments, with a negative synergistic effect on photosynthetic yield observed at 25 °C and low salinities (12, 6 SA). E. radiata died in salinities below 18 SA, except at 5 °C and L. variegata was highly susceptible to elevated temperatures (20, 25 °C). Antioxidant pool size showed species-specific responses to the experimental conditions, being most resilient in U. pinnatifida. Overall, U. pinnatifida displayed broader tolerance to the experimental salinity and temperature conditions than native kelps. The abilities to cope with a wide range in abiotic factors and to thrive in estuarine conditions might contribute to higher competitive strength compared to native kelps leading to its invasion success, especially with regard to ocean warming.

The in hospite Symbiodinium symbiont of corals on shallow reefs relies on photoprotection and photorepair during periods of exposure to short-term high light and/or temperature stress. A coral’s susceptibility to bleaching is species specific and determined not only by Symbiodinium type, size and physiology, but also by coral host features. Here, photoprotective, photorepair, photochemical and non-photochemical efficiency parameters of Symbiodinium harboured in two morphologically different coral species were examined on Heron Island (23.4420°S, 151.9140°E) in July 2011. The two coral species were exposed to high light stress for 96 h, with or without inhibition of photosystem (PS) II repair by lincomycin. Symbiodinium harboured in Pocillopora damicornis showed an increase in xanthophyll de-epoxidation under high light exposure, whereas algal symbionts in Pavona decussata showed constant levels of xanthophyll de-epoxidation. High light-treated specimens of P. damicornis maintained steady PsbA protein (D1 protein) content throughout the experiment, but P. decussata showed a peak in PsbA protein content after 48 h of exposure. In hospite Symbiodinium in P. damicornis had greater content of PsbA protein fragments, suggesting higher accumulation of photodamaged products, compared to Symbiodinium in P. decussata, where both maintained steady PSII photochemical capacity over 96 h of exposure. Under inhibition of PSII repair, both species lost PsbA protein content and PSII photochemical capacity. Both species showed increased heat dissipation under inhibition of PSII repair, but differed in photoprotective strategies and photorepair activity. Our results suggest that, as well as any differences in the symbiont, characteristics of the coral host can alter important physiological responses in Symbiodinium.

This study examined the capacity for photoprotection and repair of photo-inactivated photosystem II in the same Symbiodinium clade associated with two coexisting coral species during high-light stress in order to test for the modulation of the symbiont’s photobiological response by the coral host. After 4 days exposure to in situ irradiance, symbionts of the bleaching-sensitive Pocillopora damicornis showed rapid synthesis of photoprotective pigments (by 44 %) and strongly enhanced rates of xanthophyll cycling (by 446 %) while being insufficient to prevent photoinhibition (sustained loss in Fv/Fm at night) and loss of symbionts after 4 days. By contrast, Pavona decussata showed no significant changes in Fv/Fm, symbiont density or xanthophyll cycling. Given the association with the same Symbiodinium clade in both coral species, our findings suggest that symbionts in the two species examined may experience different in hospite light conditions as a result of different biometric properties of the coral host.

Since pre-industrial times, uptake of anthropogenic CO2 by surface ocean waters has caused a documented change of 0.1 pH units. Calcifying organisms are sensitive to elevated CO2 concentrations due to their calcium carbonate skeletons. In temperate rocky intertidal environments, calcifying and noncalcifying macroalgae make up diverse benthic photoautotrophic communities. These communities may change as calcifiers and noncalcifiers respond differently to rising CO2 concentrations. In order to test this hypothesis, we conducted an 86 d mesocosm experiment to investigate the physiological and competitive responses of calcifying and noncalcifying temperate marine macroalgae to 385, 665, and 1486 mu atm CO2. We focused on comparing 2 abundant red algae in the Northeast Atlantic: Corallina officinalis (calcifying) and Chondrus crispus (noncalcifying). We found an interactive effect of CO2 concentration and exposure time on growth rates of C. officinalis, and total protein and carbohydrate concentrations in both species. Photosynthetic rates did not show a strong response. Calcification in C. officinalis showed a parabolic response, while skeletal inorganic carbon decreased with increasing CO2. Community structure changed, as Chondrus crispus cover increased in all treatments, while C. officinalis cover decreased in both elevated-CO2 treatments. Photochemical parameters of other species are also presented. Our results suggest that CO2 will alter the competitive strengths of calcifying and noncalcifying temperate benthic macroalgae, resulting in different community structures, unless these species are able to adapt at a rate similar to or faster than the current rate of increasing sea-surface CO2 concentrations.