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Concrete is a widely used building material in coastal constructions worldwide. However, limited natural resources used in the production process, as well as high CO2-emission due to the calcination process of limestone and the thermal energy demand for Portland cement clinker production, raise the demand for alternative constituents. Alternative mixture types should be environmentally friendly and, at best, mimic natural hard substrates. Here five different concrete mixtures, containing different cements (Portland cement and blast furnace cements) and aggregates (sand, gravel, iron ore and metallurgical slags) were made. Three replicate cubes (15 × 15 × 15 cm) of each type were then deployed in a German deep-water Port, the JadeWeserPort, to study benthic community establishment after one year. Results are compared to a similar experiment conducted in a natural hard ground environment (Helgoland Island, Germany). Results indicate marked differences in settled communities in the Port site compared to natural environments. At the Port site community composition did not differ with the concrete mixtures. Surface orientation of the cubes (front/top/back) revealed significant differences in species abundances and compositions. Cubes hold more neobiota in the Port site than in natural hard ground environments. Implications for the usage of new concrete mixtures are discussed.

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.

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

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...

International audience; 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.

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. Foundation for Science and Technology: UIDB/04326/2020/ PTDC/MAR-EST/6053/2014/ Biodiversa/0004/2015 info:eu-repo/semantics/publishedVersion

The Arctic climate is changing rapidly. The warming and resultant longer open water periods suggest a potential for expansion of marine vegetation along the vast Arctic coastline. We compiled and reviewed the scattered time series on Arctic marine vegetation and explored trends for macroalgae and eelgrass (Zostera marina). We identified a total of 38 sites, distributed between Arctic coastal regions in Alaska, Canada, Greenland, Iceland, Norway/Svalbard, and Russia, having time series extending into the 21st Century. The majority of these exhibited increase in abundance, productivity or species richness, and/or expansion of geographical distribution limits, several time series showed no significant trend. Only four time series displayed a negative trend, largely due to urchin grazing or increased turbidity. Overall, the observations support with medium confidence (i.e., 5–8 in 10 chance of being correct, adopting the IPCC confidence scale) the prediction that macrophytes are expanding in the Arctic. Species distribution modeling was challenged by limited observations and lack of information on substrate, but suggested a current (2000–2017) potential pan-Arctic brown macroalgal distribution area of 655,111 km2(140,433 km2intertidal, 514,679 km2subtidal), representing an increase of about 45% for subtidal- and 8% for intertidal macroalgae since 1940–1950, and associated polar migration rates averaging 18–23 km decade–1. Adjusting the potential macroalgal distribution area by the fraction of shores represented by cliffs halves the estimate (340,658 km2). Warming and reduced sea ice cover along the Arctic coastlines are expected to stimulate further expansion of marine vegetation from boreal latitudes. The changes likely affect the functioning of coastal Arctic ecosystems because of the vegetation’s roles as habitat, and for carbon and nutrient cycling and storage. We encourage a pan-Arctic science- and management agenda to incorporate marine vegetation into a coherent understanding of Arctic changes by quantifying distribution and status beyond the scattered studies now available to develop sustainable management strategies for these important ecosystems.

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.

The rhodophytes Mastocarpus stellatus and Chondrus crispus occupy the lower intertidal zone of rocky shores along North Atlantic coastlines, with C. crispus generally occurring slightly deeper. Consequently, M. stellatus is exposed to more variable environmental conditions, related to a generally higher stress tolerance of this species. In order to extend our understanding of seasonal modulation of stress tolerance, we subjected local populations of M. stellatus and C. crispus from Helgoland, North Sea, to short-term high-light stress experiments over the course of a year (October 2011, March, May and August 2012). Biochemical analyses (pigments, antioxidants, total lipids, fatty acid compositions) allowed to reveal mechanisms behind modulated high-light tolerances. Overall, C. crispus was particularly more susceptible to high-light at higher water temperatures (October 2011 and August 2012). Furthermore, species-specific differences in antioxidants, total lipid levels and the shorter-chain/longer-chain fatty acid ratio (C14 + C16/C18 + C20) were detected, which may enhance the tolerance to high-light and other abiotic stress factors in M. stellatus, so that this species is more competitive in the highly variable upper intertidal zone compared to C. crispus. Since the high-light tolerance in C. crispus seemed to be affected by water temperature, interactions between both species may be impacted in the future by rising mean annual sea surface temperature around the island of Helgoland.

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

In some parts of the Southern Ocean (SO), even though low surface concentrations of iron (Fe) and manganese (Mn) indicate FeMn co-limitation, we still lack an understanding on how Mn and Fe availability influences SO phytoplankton ecophysiology. Therefore, this study investigated the effects of Fe and Mn limitation alone as well as their combination on growth, photophysiology and particulate organic carbon production of the bloom-forming Antarctic diatom Chaetoceros debilis. Our results clearly show that growth, photochemical efficiency and carbon production of C. debilis were co-limited by Fe and Mn as highest values were only reached when both nutrients were provided. Even though Mn-deficient cells had higher photochemical efficiencies than Fe-limited ones, they, however, displayed similar low growth and POC production rates, indicating that Mn limitation alone drastically impeded the cell's performance. These results demonstrate that similar to low Fe concentrations, low Mn availability inhibits growth and carbon production of C. debilis. As a result from different species-specific trace metal requirements, SO phytoplankton species distribution and productivity may therefore not solely depend on the input of Fe alone, but also critically on Mn acting together as important drivers of SO phytoplankton ecology and biogeochemistry.

Saccharina latissima is an economically and ecologically relevant kelp species in Europe and North America. In kelps, the sexuality is expressed during the haploid life stage and the microscopic gametophytes exhibit significant sexual dimorphism. To understand the sex-dependent impact of temperature on the gametophyte stage, we analyzed for the first time, gene expression profiles of male and female gametophytes at three different temperatures (4°C, 12°C and 20°C) characteristic for the species distribution range by using RNA-sequencing. We identified several differentially expressed genes between sexes; while female biased genes were enriched in general metabolism and energy production, male biased genes function within cell cycle and signaling. In our study, temperature modulated sex-biased gene expression, with only a small percentage of differentially expressed genes consistently male (7%) or female-biased (12%) at the three temperatures. Female gametophytes responded stronger to higher temperatures than males, suggesting that males are more heat tolerant. Differences between S. latissima and other brown algal gender-dependent gene expression might mirror the different evolutionary and ecological contexts. Genomic information on kelp gametophyte is still scarce and thus this study adds to our knowledge on sex differences in abiotic stress responses in macroalgae at the transcriptomic level.HighlightThe transcriptomic basis for sexual dimorphism and associated metabolic needs are described for the kelp Saccharina latissima. Temperature modulates sex-biased gene expression resulting in a stronger stress response in females.

Due to its year-round accessibility and excellent on-site infrastructure, Kongsfjorden and the Ny-Alesund Research and Monitoring Facility have become established as a primary location to study the impact of environmental change on Arctic coastal ecosystems. Due to its location right at the interface of Arctic and Atlantic oceanic regimes, Kongsfjorden already experiences large amplitudes of variability in physico/chemical conditions and might, thus, be considered as an early warning indicator of future changes, which can then be extrapolated in a pan-Arctic perspective. Already now, Kongsfjorden represents one of the best-studied Arctic fjord systems. However, research conducted to date has concentrated largely on small disciplinary projects, prompting the need for a higher level of integration of future research activities. This contribution, thus, aims at identifying gaps in knowledge and research priorities with respect to ecological and adaptive responses to Arctic ecosystem changes. By doing so we aim to provide a stimulus for the initiation of new international and interdisciplinary research initiatives.

Although iron (Fe) availability primarily sets the rate of phytoplankton growth and primary and export production in the Southern Ocean, other environmental factors, most significantly light, also affect productivity. As light availability strongly influences phytoplankton species distribution in low Fe-waters, we investigated the combined effects of increasing light (20, 200 and 500 μmol photons m−2 s−1) in conjunction with different Fe (0.4 and 2 nM Fe) availability on the physiology of two ecologically relevant phytoplankton species in the Southern Ocean, Chaetoceros debilis (Bacillariophyceae) and Phaeocystis antarctica (Haptophyceae). Fe-deficient cells of P. antarctica displayed similar high growth rates at all irradiances. In comparison, Fe-deplete C. debilis cells grew much slower under low and medium irradiance and were unable to grow at the highest irradiance. Interestingly, Fe-deficient C. debilis cells were better protected against short-term excessive irradiances than P. antarctica. This tolerance was apparently counteracted by strongly lowered growth and particulate organic carbon production rates of the diatom relative to the prymnesiophyte. Overall, our results show that P. antarctica was the more tolerant species to changes in the availability of Fe and light, providing it a competitive advantage under a high light regime in Fe-deficient waters as projected for the future.

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.

The Western Antarctic Peninsula (WAP), one of the most productive regions of the Southern Ocean, is currently undergoing rapid environmental changes such as ocean acidification (OA) and increased daily irradiances from enhanced surface‐water stratification. To assess the potential for future biological CO2 sequestration of this region, we incubated a natural phytoplankton assemblage from Ryder Bay, WAP, under a range of pCO2 levels (180 μatm, 450 μatm, and 1000 μatm) combined with either moderate or high natural solar radiation (MSR: 124 μmol photons m−2 s−1 and HSR: 435 μmol photons m−2 s−1, respectively). The initial and final phytoplankton communities were numerically dominated by the prymnesiophyte Phaeocystis Antarctica, with the single cells initially being predominant and solitary and colonial cells reaching similar high abundances by the end. Only when communities were grown under ambient pCO2 in conjunction with HSR did the small diatom Fragilariopsis pseudonana outcompete P. Antarctica at the end of the experiment. Such positive light‐dependent growth response of the diatom was, however, dampened by OA. These changes in community composition were caused by an enhanced photosensitivity of diatoms, especially F. pseudonana>/i>, under OA and HSR, reducing thereby their competitiveness toward P. Antarctica. Moreover, community primary production (PP) of all treatments yielded similar high rates at the start and the end of the experiment, but with the main contributors shifting from initially large to small cells toward the end. Even though community PP of Ryder Bay phytoplankton was insensitive to the changes in light and CO2 availability, the observed size‐dependent shift in productivity could, however, weaken the biological CO2 sequestration potential of this region in the future.

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.

The global trend of unprecedented losses in coral reefs is particularly striking in the Caribbean, where dense algal assemblages are commonly replacing corals. So far, hardly anything is known about the ecology of the dominant algal groups. The present study compiled records of Chlorophytes from nine studies in the shallow reefs of Curaçao in the years preceding the onset of coral reef decline (1908–1978) and compared them with records from three recent (2007–2009) expeditions conducted at the same and nearby study locations along the south-west coast of the island. A total of 107 species were encountered, including seven new records for Curaçao (Anadyomene saldanhae, Bryopsis hypnoides, Chaetomorpha minima, Derbesia fastigiata, Ulva flexuosa subsp. paradoxa, Ulvella scutata and Ulvella lens). Sampled material revealed a higher species number during the dry seasons than during the wet seasons, indicating a seasonal variation in algal growth. Most species grew on hard substratum or were epibiotic, and 13 species were found growing on more than one substratum. Comparisons with earlier studies suggest an extension in depth range for nine species. The present work provides a comprehensive overview of the distribution of Chlorophytes of the island and can serve as an important baseline for further research on coral reef ecosystem changes. Fil: Fricke, Anna Lena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Leibniz Centre for Tropical Marine Research; Alemania Fil: Titlyanova, Tamara V.. Far Eastern Branch of the Russian Academy of Sciences; Rusia Fil: Teichberg, Mirta. Leibniz Centre for Tropical Marine Research; Alemania Fil: Nugues, Maggy M.. Paris Sciences et Lettres Research University; Francia. Centre de Recherches Insulaires et Observatoire de l’Environnement; Polinesia Francesa. Caribbean Research and Management of Biodiversity; Antillas Neerlandesas Fil: Bakai, Romina Vanesa. Universitat Bremen; Alemania

Seagrass meadows are a crucial component of tropical marine reef ecosystems. Seagrass plants are colonized by a multitude of epiphytic organisms that contribute to broadening the ecological role of seagrasses. To better understand how environmental changes like ocean acidification might affect epiphytic assemblages, the microbial community composition of the epiphytic biofilm of Enhalus acroides was investigated at a natural CO2 vent in Papua New Guinea using molecular fingerprinting and next-generation sequencing of 16S and 18S rRNA genes. Both bacterial and eukaryotic epiphytes formed distinct communities at the CO2 -impacted site compared with the control site. This site-related CO2 effect was also visible in the succession pattern of microbial epiphytes. We further found an increased relative sequence abundance of bacterial types associated with coral diseases at the CO2 -impacted site (Fusobacteria, Thalassomonas), whereas eukaryotes such as certain crustose coralline algae commonly related to healthy reefs were less diverse. These trends in the epiphytic community of E. acroides suggest a potential role of seagrasses as vectors of coral pathogens and may support previous predictions of a decrease in reef health and prevalence of diseases under future ocean acidification scenarios.

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.

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.

Photosynthesis at high latitudes demands efficient strategies of light utilization to maintain algal fitness and performance. The fitness, and physiological adaptation, of a plant or algae species depends in part on the abundance and efficiency of the pigments it can produce to utilize the light resource from its environment. We quantified pigment composition and concentration in six species of the brown macroalgal genus Desmarestia, collected from sub-Antarctic sites (Strait of Magellan, Beagle Channel–Cape Horn Province) and sites on the Antarctic Peninsula and adjacent islands. Sub-Antarctic Desmarestia species exhibited lower concentrations of chlorophyll a , chlorophyll c and fucoxanthin than endemic Antarctic species. Antarctic samples of D. menziesii and D. antarctica collected along a decreasing latitudinal gradient showed spatial and interspecific differences in light-harvesting pigment composition. Our results suggest distinct physiological adjustments in Desmarestia species in response to heterogeneous abiotic environmental conditions. The marine sub-Antarctic and Antarctic ecosystems are characterized by harsh environments (e.g., extreme irradiance, photoperiod, temperature, salinity) to which the physiology of macroalgal species must adapt. Keywords: Macroalgae; Phaeophyceae; photosynthesis; physiology; environmental heterogeneity; Chile. (Published: 4 August 2016) Citation: Polar Research 2016, 35 , 29383,http://dx.doi.org/10.3402/polar.v35.29383

Coral bleaching is the manifestation of the dysfunction of the symbiosis between scleractinian corals and dinoflagellates of the diverse genus Symbiodinium and is induced by elevated temperatures and high irradiance. We investigated the photophysiological response of two genetically distinct Symbiodinium subtypes within clade A upon exposure to elevated temperatures at two light intensities for 3 weeks. While both subtypes displayed a characteristic photoacclimation to high light (HL) (decrease in light-harvesting pigments, lower photochemical efficiency of photosystem II, increased xanthophyll pool sizes), the tolerance toward thermal stress clearly differed between the two subtypes. Symbiodinium Ax was highly susceptible to chronic photoinhibition at temperatures ≥30°C, which was exacerbated under HL conditions. A1 showed a capacity for photoacclimation and high thermal tolerance, which might be related to higher cellular concentrations of photoprotective xanthophylls and the low-molecular antioxidant glutathione (GSx) along with the dynamic regulation of these photoprotective pathways. Whereas HL conditions induced both accumulation of diatoxanthin and GSx, thermal stress further stimulated xanthophyll cycling, which might compensate for diminished amounts of GSx at elevated temperatures. Our results show that the two clade A subtypes clearly differ in their strategies to cope with thermal stress in combination with high irradiance.

Future atmospheric CO2 levels will most likely have complex consequences for marine organisms, particulary photosynthetic calcifying organisms. Corallina officinalis L. is an erect calcifying macroalga found in the inter- and subtidal regions of temperate rocky coastlines and provides important substrate and refugia for marine meiofauna. The main goal of the current study was to determine the physiological responses of C. officinalis to increased CO2 concentrations expected to occur within the next century and beyond. Our results show that growth and production of inorganic material decreased under high CO2 levels, while carbonic anhydrase activity was stimulated and negatively correlated to algal inorganic content. Photosynthetic efficiency based on oxygen evolution was also negatively affected by increased CO2. The results of this study indicate that C. officinalis may become less competitive under future CO2 levels, which could result in structural changes in future temperate intertidal communities. Federal Ministry of Education & Research (BMBF)

Enhanced UV-radiation (UVR) through stratospheric ozone depletion and global warming are crucial stressors to marine macroalgae. Damages may arise through formation of reactive oxygen species (ROS) in gametophytes of ecologically important kelps, brown algae of the order Laminariales, Such stress-induced damages may have a negative impact on their fitness and further impact their following life stages. In our study, gametophytes of three kelp species Alaria esculenta (L.) Grev., Laminaria digitata (Huds.) Lamour., Saccharina latissima (L.) Lane, Mayes, Druehl, Saunders from the Arctic, and of L. hyperborea (Gunnerus) Foslie from the North Sea were exposed to photosynthetically active radiation, UV-A, and UV-B radiation and four temperatures (2–18°C). ROS are formed predominantly in the peripheral cytoplasm and in chloroplasts especially after exposure to UVR. Superoxide (O2*-) is additionally formed in small, globular cytoplasmic structures, possibly mitochondria. In the surrounding medium O2*--concentration increased markedly at elevated temperatures and under UV stress in some cases. Ultrastructural damage was negligible pointing to a high stress tolerance of this developmental stage. Our data indicate that stress tolerant gametophytes of three Arctic kelp species should sustain their crucial function as seed bank for kelp populations even under prospective rising environmental perturbations.

Radiation damage can inter alia result in lipid peroxidation of macroalgal cell membranes. To prevent photo-oxidation within the cells, photoprotective substances such as phlorotannins are synthesized. In the present study, changes in total fatty acids (FA), FA composition and intra/extracellular phlorotannin contents were determined by gas chromatography and the Folin-Ciocalteu method to investigate the photoprotective potential of phlorotannins to prevent lipid peroxidation. Alaria esculenta juveniles (Phaeophyceae) were exposed over 20 days to high/low photosynthetically active radiation (PAR) in combination with UV radiation (UVR) in the treatments: PAB (low/high PAR + UV-B + UV-A), PA (low/high PAR + UV-A) or low/high PAR only. While extracellular phlorotannins increased after 10 days, intracellular phlorotannins increased with exposure time and PA and decreased under PAB. Interactive effects of time:radiation wavebands, time:PAR dose as well as radiation wavebands:PAR dose were observed. Low FA contents were detected in the PA and PAB treatments; interactive effects were observed between time:high PAR and PAB:high PAR. Total FA contents were correlated to extra/intracellular phlorotannin contents. Our results suggest that phlorotannins might play a role in intra/extracellular protection by absorption and oxidation processes. Changes in FA content/composition upon UVR and high PAR might be considered as an adaptive mechanism of the A. esculenta juveniles subjected to variations in solar irradiance.

Steinhoff F.S., Wiencke C., Wuttke S. and Bischof K. 2011. Effects of water temperatures, UV radiation and low vs high PAR on phlorotannin content and germination in zoospores of Saccorhiza dermatodea (Tilopteridales, Phaeophyceae). Phycologia 50: 256–263. DOI: 10.2216/09-107.1 Global climate change will have multiple effects on our environment and might especially change marine coastal ecosystems and their communities due to rising water temperatures and changing light regimes in the water column. Due to the key role of zoospores in the life-history cycle of kelps, we investigated how zoospores of the shallow water species Saccorhiza dermatodea (B. de la Pylaie) J.E. Areschoug respond to interactive effects of changing water temperatures, low/high photosynthetically active radiation (PAR) and UV radiation (UVR). Zoospores were examined with respect to germination pattern (germination rates, light micrographs) and phlorotannin content (Folin–Ciocalteu method). In summer 2007, we exposed S. dermat...

Spores and gametophytes are considered to be those life-history stages of kelps most susceptible to environmental perturbations and, in particular, to temperature and UV radiation. Microstages of Arctic (Saccharina latissima, Laminaria digitata, Alaria esculenta from Spitsbergen) and temperate kelp species (S. latissima, L. digitata, L. hyperborea from the North Sea) were exposed in 2-factorial experiments to different temperatures (2 to 18°C) and radiation conditions (photosyn- thetic active radiation, UV-A radiation, UV-B radiation). Our results reveal ecotypic differentiations in the stress responses of zoospores of L. digitata and S. latissima from the Arctic and North Sea. UV- A radiation either enhanced the formation of gametes at elevated temperatures in L. digitata or impaired egg release and subsequent sporophyte formation in L. hyperborea. Microstages exposed to additional UV-B radiation were strongly inhibited to a population-, species- and life phase-specific degree at suboptimal and optimal temperatures. Only gametogenesis of Laminaria spp. was shown to be tolerant to UV-B exposure. Conclusively, in respect to a future scenario of elevated UV radiation regimes and higher summer temperatures in Arctic and North Sea waters, summer-recruiting Arctic species and L. digitata from the North Sea might become endangered by a frequent disturbance of their microstages.

For many coastal areas of the world, a decrease in abundance and depth penetration of perennial macroalgae and seagrasses has been documented and attributed to eutrophication. A surplus of nutrients impairs perennial seaweeds in at least two ways: increased phytoplankton densities reduce the depth penetration of light and in addition filamentous seaweeds and microalgae growing epiphytically shade their perennial hosts. A reduction of depth limit and total abundance has also been observed for the brown seaweed Fucus vesiculosus at many sites in the Baltic Sea. However, in most cases the mechanistic reason for the loss of Fucus has been deduced from observations rather than from experimental evidence. Here, we present results of a two-factorial (water depth/light supply and epibionts) experiment that was run in the Kiel Fjord, western Baltic, from August to October 2005. Performance of F. vesiculosus was recorded by growth and chlorophyll measurements, PI-curves and in situ measurements of the photosynthetic activity as the relative rate of electron transport (rETR). rETR and growth decreased with water depth. Chlorophyll a concentrations increased with reduced light intensities, but this apparently could not compensate for the light deficiency. Epibionts enhanced the negative effect of reduced light conditions on growth. According to these findings we estimated the physiological depth limit of F. vesiculosus in the Kiel Fjord to lie between 4 and 6 m water depth.

The interactive effects of an 8 h exposure to UV radiation and altered temperatures on the ultrastructure and germination of zoospores of the sublittoral brown alga Laminaria hyperborea (Gunn.) Foslie were investigated for the first time. Spores were exposed to four temperatures (2, 7, 12 and 17 degrees C) and three light regimes (PAR, PAR + UV-A, PAR + UV-A+UV-B). Freshly-released spores of L. hyperborea lack a cell wall and contain a nucleus with fine granular nucleoplasm and a nucleolus, one chloroplast, several mitochondria, dictyosomes and an endoplasmatic reticulum. Further, several kinds of so-called adhesive vesicles, lipid globuli and physodes containing UV-absorbing phlorotannins are embedded in the cytoplasm. No eye-spot is present. Physodes were found but they were rare and small. After an 8 h exposure to UV-B, the nucleoplasm had a mottled structure, chloroplasts contained plastoglobuli, the structure of the mitochondria changed from crista- to sacculus-type and germination was strongly inhibited at all temperatures. UV-A only had an impact on the ultrastructure at the highest temperature tested. The strongest effects were found at 17 degrees C, where germination was reduced to 35%, 32% and 9% after exposure to PAR, PAR+UV-A and PAR + UV-A + UV-B, respectively. This study indicates that UV-B radiation has strong damaging effects on the physiology and ultrastructure of zoospores of L. hyperborea. The results are important for developing scenarios for the effect of enhanced UV radiation and increasing temperatures caused by global climate changes.

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.

The reproductive cells of macroalgae are regarded as the life history stages most susceptible to various environmental stresses, including UV radiation (UVR). UVR is proposed to determine the upper depth distribution limit of macroalgae on the shore. These hypotheses were tested by UV-exposure experiments, using spores and young thalli of the eulittoral Rhodophyceae Mastocarpus stellatus and Chondrus crispus and various sublittoral brown macroalgae (Phaeophyceae) with different depth distribution from Helgoland (German Bight) and Spitsbergen (Arctic). In spores, the degree of UV-induced inhibition of photosynthesis is lower in eulittoral species and higher in sublittoral species. After UV stress, recovery of photosynthetic capacity is faster in eulittoral compared to sublittoral species. DNA damage is lowest while repair of DNA damage is highest in eulittoral compared to sublittoral species. When the negative impact of UVR prevails, spore germination is inhibited. This is observed in deep water kelp species whereas the same UVR doses do not inhibit germination of shallow water kelp species. A potential acclimation mechanism to increase UV tolerance of brown algal spores is the species-specific ability to increase the content of UV-absorbing phlorotannins in response to UV-exposure. Growth rates of young Mastocarpus and Chondrus gametophytes exposed to experimental doses of UVR are not affected while growth rates of all young kelp sporophytes exposed to UVR are significantly lowered. Furthermore, morphological UV damage in Laminaria ochroleuca includes tissue deformation, lesion, blistering and thickening of the meristematic part of the lamina. The sensitivity of young sporophytes to DNA damage is correlated with thallus thickness and their optical characteristics. Growth rate is an integrative parameter of all physiological processes in juvenile plants. UV inhibition of growth may affect the upper distribution depth limit of adult life history stages. Juveniles possess several mechanisms to minimize UVR damage and, hence, are less sensitive but at the expense of growth. The species-specific susceptibility of the early life stages of macroalgae to UVR plays an important role for the determination of zonation patterns and probably also for shaping up community structure.