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Mitogen-Activated Protein Kinases (MAPKs) are a group of cytoplasmic phosphoproteins that constitute the central core of the signalling network to respond to stress in most organisms. Their role in stress responses has been extensively studied in organisms from yeast to humans, and recently, their presence has also been described in higher plants as well as in micro- and macroalgae. In this study, we demonstrate via short experiments (1 h in duration), the rapid activation of two MAPKs similar to p38 and JNK of mammalian cells, in the Arctic kelps Laminaria solidungula and Saccharina latissima exposed to temperature and UV stress. The molecular mass of p38 is 40 KDa in L. solidungula and 42 KDa in S. latissima, while two JNKs were detected in both species, of 36 and 42 KDa in L. solidungula, and 36 and 40 KDa in S. latissima. These MAPKs are highly phosphorylated in response to temperature and UV light. In S. latissima, both p38 and the JNK showed higher phosphorylation at 2C than at 7C, while the reverse response was shown for L. solidungula. In addition, a significant increase in phosphorylation of both kinases was found following exposure to UV radiation (UVR). Exposure to PAR+UVA+UVB induced higher phosphorylation than PAR+UVA in L. solidungula, especially at 7C. In S. latissima, this response occurred only with JNK, and no differences in p38 phosphorylation between PAR+UVA and PAR+UVA+UVB at any temperature were observed. These results indicate the possible participation of MAPK-like proteins in response to stress in Arctic kelps, and that their activation is species-specific.

Seaweeds, also known as macroalgae, are among the most important primary producers and act as ecological engineers on rocky coasts of the world’s oceans. In addition to their extreme ecological importance they are also of high economic relevance. Complementing available textbooks with its more research-oriented approach, this volume contains 22 chapters by renowned experts, grouped in five parts. In Part I fundamental processes and acclimation strategies of seaweeds towards the abiotic environment are covered. Part II focuses on the multitude of biotic interactions in seaweed communities, and in Part III the reader is introduced to the structure and function of the main seaweed systems of the world. The chapters of Part IV highlight and discuss the effects of global and local environmental changes on seaweeds and their communities. In the final Part V a comprehensive overview of developments in seaweed aquaculture, industrial applications and the overall economic importance of seaweeds is provided. Summarizing the advances in seaweed biology achieved within the last few decades, this book also identifies gaps in the present knowledge and needs for future research.

Seaweeds have been utilized by man as food and medication for about 14,000 years. The ever rising demand for edible seaweeds and for biochemical components of seaweeds, mainly hydrocolloids like agar, alginate, and carrageenan, has fuelled a large aquaculture industry particularly in Asia. Future expansion of seaweed culture will include suitable farming sites in offshore areas associated with wind farms. Seaweeds as extractive and therefore bioremedial species are moreover an important component in Integrated Multi-Trophic Aquaculture (IMTA), where commercially valuable organisms of different trophic levels are combined in a culturing system resembling a small ecosystem. The employment created by seaweeds and other aquaculture secures an income to millions of people and is therefore of high socioeconomic importance.

Marine macroalgae represent an important part of coastal ecosystems in temperate and polar areas. Increasing surface UV radiation (UVR) levels due to stratospheric ozone thinning may lead to deleterious effects on the physiology of marine macroalgae. Only few studies concentrate on the response of macroalgal gene expression towards elevated UVR. Analyzing gene expression in marine algae is challenging regarding RNA extraction, enrichment of differentially expressed transcripts and identification of resulting sequences. Thus, we focused on the optimization of the appropriate techniques using the widely distributed green marine macroalga Acrosiphonia arcta. We successfully used a combination of suppression subtractive hybridization (SSH) with microarray-based screening of size-selected cDNAs libraries and were able to substantially improve the outcome compared to standard techniques.

The aim of this study is to understand the macroalgal vertical zonation at Potter Cove (Isla 25 de Mayo/ King George Island) in three selected newly ice-free areas with different degree of glacial influence (low: area 1, intermediate: area 2, and high: area 3), and thus a different degree of sedimentation, from a physiological point of view. In summer 2010 and spring 2011, two macroalgal key species (Himantothallus grandifolius and Palmaria decipiens) were sampled at 5, 10, 20 and 30 m depth. After collection, photosynthesis – irradiance curves were performed and photosynthetic parameters were calculated. Photosynthetically Active Radiation (PAR) was logged continuously over 7 days during spring 2011 and summer 2012 at 0, 5, 10, 20 and 30 meters depth in each area. Subsequently, the daily metabolic carbon balance (DMCB) was determined using the obtained photosynthetic parameters and the underwater PAR data. In areas with high glacial influence the maximal vertical distribution limit of all species was 10 m depth, while in areas with intermediate and low glacial impact, it was 20 and 30 m depth, respectively. PAR values were higher in spring than in summer. For both species, DMCB values were significantly higher in spring compared to summer. In addition, both species DMCB values decreased significantly with increasing depth, and were significantly higher in areas 1 and 2 (low and intermediate glacial influence) compared to area 3 (high glacial influence). The observed vertical distribution in all the studied areas seem to be determined mainly by the spring PAR conditions, as in summer the DMCB values are too low for both species to explain their survival. Furthermore, vertical zonation of the studied species is positively correlated to the light penetration which decreases as the glacial influence (as production of sediment input) increases. A further increase of sedimentation due to global warming will undoubtedly lead to an elevation of the lower distribution limit

In natural environments, marine biotas are exposed to a variety of simultaneously acting abiotic factors. Hereof, temperature, irradiance and CO2 availability are major factors influencing the physiological performance of marine macroalgae. In order to test whether elevated levels of CO2 may remediate the otherwise reduced performance of uncalcified seaweeds under other stressful abiotic factors, we performed multi-factorial experiments with the red alga Chondrus crispus rom Helgoland (North Sea) with two levels of CO2, temperature and irradiance, respectively: Low and high pCO2 levels were tested in combination with either (1) optimal and low irradiances or (2) optimal and sub-lethal high temperatures for growth. Performance of C. 33 crispus was evaluated as biomass increase and relative growth rates (RGR), gross photosynthesis, and pigment content. Acclimation of growth and photosynthesis was measured after 4 and 8 days. Acclimation time was crucial for elucidating single or combined CO2 effects on growth and photosynthesis. Significant CO2 effects became evident only in combination with either elevated temperature or reduced irradiance. Growth and photosynthesis showed divergent pattern: the RGR and biomass significantly increased only under a combination of high pCO2 and elevated temperature; gross photosynthesis was significantly reduced under high pCO2 conditions at low irradiance. Pigment content varied in response to irradiance and temperature,respectively, but was independent of pCO2.

Macroalgae in Kongsfjorden were surveyed by divers down to 30 m depth at Hansneset, Blomstrand (78° 39’N, 11°57’E). In total, 62 species were identified, 16 Chlorophyta, 25 Phaeophyceae and 21 Rhodophyta. The majority of species (53.5%) belonged to the Arctic cold-temperate group, followed by species distributed from the Arctic to the warm-temperate region (25.9%). Four endemic Arctic species (Laminaria solidungula, Acrosiphonia flagellata, A. incurva, Urospora elongata) were found. Two species (Lithosiphon filiformis, Mikrosyphar polysiphoniae) were new for Svalbard. Chlorophyta, Phaeophyceae and Rhodophyta extended from the eulittoral zone down to 11, 21 and >30 m depths, with maximum biomasses at 1- 5 m, 5- 10 m and 5- 30 m depth, respectively. Annual and pseudoperennial species had highest biomasses in the upper 5 m, while perennials were distributed deeper. The highest biomass (8600 g m-2) at 5 m depth included mainly Laminaria digitata, Saccorhiza dermatodea, Alaria esculenta and Saccharina latissima. The biogeographic composition of macroalgae at Hansneset was relatively similar to that of Northeast Greenland, but different from that of Northern Norway, which is characterised by a higher proportion of temperate species. Climate warming and ship traffic may extend some of the distribution ranges of macroalgae from mainland Norway to Svalbard.

Kelps, brown algae of the order Laminariales, dominate rocky shores and form huge kelp beds which provide habitat and nurseries for various marine organisms. Whereas the basic physiological and ecophysiological characteristics of kelps are well studied, the molecular processes underlying acclimation to different light and temperature conditions are still poorly understood. Therefore we investigated the molecular mechanisms underlying the physiological acclimation to light and temperature stress. Sporophytes of S. latissima were exposed to combinations of light intensities and temperatures, and microarray hybridizations were performed to determine changes in gene expression patterns. This first large-scale transcriptomic study of a kelp species shows that S. latissima responds to temperature and light stress with a multitude of transcriptional changes: up to 32% of genes showed an altered expression after the exposure experiments. High temperature had stronger effects on gene expression in S. latissima than low temperature, reflected by the higher number of temperature-responsive genes. We gained insights into underlying molecular processes of acclimation, which includes adjustment of the primary metabolism as well as induction of several ROS scavengers and a sophisticated regulation of Hsps. We show that S. latissima, as a cold adapted species, must make stronger efforts for acclimating to high than to low temperatures. The strongest response was caused by the combination of high temperatures with high light intensities, which proved most harmful for the alga.

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.

To elucidate dietary preferences of benthic grazers at the Arctic Kongsfjorden by means of fatty acid trophic markers, ten different parallel treatments (starvation, 3 species of red macroalgae, 4 species of brown macroalgae and 2 species of green macroalgae) were offered as mono-algal diet to specimens of the dominant sea urchin Strongylocentrotus droebachiensis (Echinodermata, Echinoidea) and the gammarid amphipod Gammarellus homari (Crustacea, Amphipoda). At the end of the 3-week feeding experiments, amphipods and sea urchins (soft tissue) were deep-frozen and analysed for total lipid contents as well as fatty acid (FA) compositions. In addition, FA profiles of the algal species were determined and screened for specific FA patterns or single FAs qualifying as potential trophic markers in the grazers. Despite their diets of nine algalspecies with different FA compositions, FA patterns of the sea urchins and amphipods revealed a pronounced similarity between treatments. This strong similarity was also observed in the faecal pellets of the sea urchins. Hence, deviating FA compositions of the macroalgae were neither reflected in the FA patterns of the grazers’ tissue nor in their faecal pellets. Suitable algal FA trophic markers could thus not be identified in the two grazers from Kongsfjorden. The rather low lipid levels, especially in the amphipods, as well as a pronounced degradation and modification of FAs may explain that the FA trophic marker approach did not provide evidence of dietary preferences. Future experiments may obtain a higher resolution of potential FA trophic markers by analysing separate lipid classes or single tissues of lipid-poor grazers. Alternatively, different methods are needed to reveal high-resolution trophic relationships between macroalgae and herbivores in Kongsfjorden.

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.

Polar seaweeds typically begin to grow in late winter-spring, around the time of sea-ice break up. They can grow under very low light enabling distributions to depths of ≥40 m. Moreover, they are physiologically adapted to low temperatures. Intertidal species exhibit a remarkable stress tolerance against freezing, desiccation and salinity changes. Endemism is much greater in the Antarctic compared to the Arctic species. On rocky shores of the Antarctic Peninsula and of Spitsbergen >80% of the bottom can be covered by seaweeds with standing biomass levels ≥20 kg wet wt m-2. Species richness and biomass declines, however, towards higher latitudes. Seaweeds are the dominant organisms in coastal waters and thus play important roles in benthic food webs and are likely to be of particular importance to benthic detrital food chains. Chemical defenses against herbivores are common in Antarctic, but not in Arctic seaweeds. More research is needed especially to study the effects of global climate changes.

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.

Palmaria decipiens (Reinsch) R.W. Ricker (1987) represents one of the dominant rhodophyte species in Antarctic coastal ecosystems. Due to its high abundance in the intertidal and upper subtidal it plays a key role in ecosystem structure and function, providing habitat, food and shelter for a multitude of associated organisms. The physiology, reproductive strategy and life cycle of P. decipiens is considered as being well adapted to the Antarctic environment, which is characterized by permanent low water temperatures and a strong seasonality in light climate. With its obvious ecological significance and adaptive strategies P. decipiens was frequently studied as a typical representative of an endemic Antarctic macroalga. Here we provide an overview of the recent literature, summarizing the knowledge gained about the alga during the last 25 years. This review focuses on the species life cycle and physiological responses, such as temperature requirements,photosynthetic characteristics, pigment content and protective mechanisms with regard to enhanced ultraviolet radiation (UV-B radiation, 280–315 nm and UV-A radiation, 315–400nm). The ecology of P. decipiens is reviewed focussing on grazing activity and abundance patterns. Since most studies on P. decipiens have been conducted at King George Island off the western Antarctic Peninsula this overview serves as a summary of baseline data from an ecosystem particularly prone to environmental change.

Exposure of the filamentous turf green alga Urospora penicilliformis to ambient and artificial ultraviolet radiation (UVR) revealed a considerable resilient species. This explains the ability of this alga to thrive in the middleupper intertidal zones of the Arctic sea where it is periodically exposed to environmental extremes. A transient UVR effect on photosynthesis under photosynthetically active radiation (PAR) + UV-A and PAR + UV-A + UV-B was found, but dynamic recovery of photoinhibition was observed immediately after reduction of the photon fluence rate of PAR in the absence or presence of background UVR under laboratory and natural solar radiation, respectively. Chlorophylls, carotenoids, and xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin) concentrations were not significantly different between freshly collected samples and filaments exposed to additional laboratory radiation treatment. The ultrastructure of the U. penicilliformis gametophytes showed that the cells are well adapted to UVR. No significant ultrastructural alterations were observed in filaments exposed to different spectral irradiance in the laboratory compared to in situ acclimated specimen. The antioxidant α-tocopherol was detected in minute quantity while the search for flavonoid-like compounds was negative. Other UV screening strategies or certain genetically fixed physiological protective mechanism could be operating in this species responsible for their occurrence in higher shoreline and ecological success. Further molecular and biochemical studies are needed to elucidate the stress resistance in this turf alga. There is an indication that the extremely thick cell wall of U. penicilliformis gametophytes covered with mucilage sheath and dense layer of mineral depositions may provide a shield against unfavorable environmental conditions in general and against UVR in particular.

During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline of Kongsfjorden (Svalbard, Norway) at ≤5 m water depth and at two stations at five different water depths (5, 10, 15, 20, 30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment cores under controlled light (ca. 100 μmol photons m−2 s−1) and temperature (2–4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down to 30 m showed high biomass of up to 317 mg chl a m−2. In spite of increasing water depth, no significant trend in “photoautotrophic active biomass” (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from ≤5 to 30 m water depth exhibited variable rates of net production from −19 to +40 mg O2 m−2 h−1 (−168 to +360 mg C m−2 day−1) and gross production of about 2–62 mg O2 m−2 h−1 (17–554 mg C m−2 day−1), which is comparable to other polar as well as temperate regions. No relation between photoautotrophic biomass and gross/net production values was found. Microphytobenthos demonstrated significant rates of primary production that is comparable to pelagic production of Kongsfjorden and, hence, emphasised the importance as C source for the zoobenthos.

The aim of this study is to understand the macroalgal vertical zonation at Potter Cove (Isla 25 de Mayo/ King George Island) in five selected areas with different degree of glacial influence, and thus a different degree of sedimentation, from a physiological point of view. From December 2009 to March 2010, five macroalgal species (Desmarestia anceps, Himantothallus grandifolius, Ascoseira mirabilis, Iridaea cordata and Palmaria decipiens) were sampled at 5, 10, 20 and 30 m depth. After collection, photosynthetic parameters and chlorophyll a content were determined. In areas with high glacial influence the maximal vertical distribution limit of all species was 10 m depth, while in areas with intermediate and low/none glacial impact, it was 20 and 30 m depth, respectively. Areas with high glacial influence presented limiting light conditions below 20 m depth coinciding with the absence of macroalgae. In intermediate and low disturbed areas, light intensities were not limiting. Palmaria decipiens was the only studied species showing lower light saturation points at deeper depths. Chl a content did not show significant differences with increasing depth. Our first results show that the vertical zonation of the studied species is positively correlated to the light penetration which decreases as the glacial influence (as production of sediment input) increases. A further increase of sedimentation due to global warming will undoubtedly lead to an elevation of the lower distribution limit of the studied species and will probably have a great effect on macroalgal primary productivity in Potter Cove.

Ultraviolet B radiation (UVBR, 280-315 nm) is known to be a stress factor for Antarctic benthic algae and invertebrates. However, there is almost no available information regarding these effects at the community level. A two-factorial colonization experiment (UVR, three levels and grazing, two levels) was performed at an intertidal and a subtidal site on King George Island/I. 25 de Mayo. Structural parameters of the community were followed for fifteen and ten weeks, respectively. The effects on the intertidal community are presented in detail in Zacher et al. Subtidal communities were dominated macroscopically by colonial diatoms and green algal filaments. Ultraviolet radiation (UVR, 280-400nm) did not affect diatoms but exerted a group-specific effect on the macroalgal assemblage. Overall, red algal cover was negatively impacted by UVR whereas for green algal filaments a significant interaction between grazing and UVR was detected. Grazers introduced a shift in both micro- and macroalgal species composition and reduced the community biomass, with stronger effects when UVBR was absent. When comparing intertidal and subtidal experiments, community architecture and biomass production was markedly different at both sites, with higher biomass and more complex diatom composition at the subtidal spot. However, UVR and grazing affected both sites in a similar pattern. Our findings suggest that UVR and grazing play a key role in shaping the subtidal and intertidal benthic algal communities in Antarctica. UVR impact on subtidal communities seemed to be more complex than in the intertidal, exerting both direct and indirect effects on the community structure.

The susceptibility of spores of the red alga Iridaea cordata and the brown algae Adenocystis utricularis and Himantothallus grandifolius to UV (UVR) and photosynthetically active radiation (PAR) was tested in field-experiments on King George Island. Spores were exposed to i) natural radiation, ii) radiation depleted of UVBR and iii) radiation depleted of UVAR and UVBR, in different water depths (1, 2, 4 and 8m). Concomitantly, spores were exposed in the laboratory for different times to artificial radiation (1, 2, 4 and 8h). Germination rates were determined after laboratory post-culture under dim white light. Germination of the intertidal species A. utricularis was not affected by depth, exposure time or radiation treatment, while germination of the other two subtidal species showed significant differences between different depth and/or radiation regimes. Spores from I. cordata and H. grandifolius were inhibited by high PAR at 1 m and 1-2 m water depth, respectively, but not in deeper waters. Spores of the two subtidal species were, in contrast to A. utricularis spores from the intertidal, affected not only by UVR but also by high PAR. In the laboratory approach under low PAR, the subtidal species were only affected by UVR under short term exposure (1-2h). Our results show that already algal spores, being the most sensitive part in the life-cycle of macroalgae, show species-specific adaptations. Not only UVR but also the high PAR fluxes penetrating into the water column in the field are important factors determining the upper distribution limit of Antarctic macroalgae.

How are benthic Antarctic communities affected by changing environmental conditions such as UV radiation (UVR)? UVR is known to affect many biological processes but almost no information exists whether these effects, visible on the molecular and cellular level, impair polar ecosystem structure. In order to obtain more information we studied the colonization of benthic primary producers in the Antarctic rocky intertidal and subtidal over a period of 106 and 70 days, respectively. 32 experimental units were installed at each site in a two-factorial design (UVR, three levels and grazers, two levels). Intertidal communities were dominated by single cell diatoms and green algal propagules. Limpet grazing reduced the algal biomass and macroalgal recruit density and further introduced a shift in both macro- and microalgal species composition. There were no negative UVR effects on the diatom assemblage. In contrast, significant UVR effects on the macroalgal assemblage were detected. UVAR (315-400nm) negatively impacted density and richness of recruits, whereas additional UVBR (280-315nm) caused a shift in species composition and led to a lower diversity of the macroalgal community by the end of the intertidal experiment. Effects were species-specific and showed that particularly young propagules were sensitive to UVR. No interactive effects of UVR and grazing were found. It is postulated that UVR has the power to change ecosystem structure in intertidal Antarctic macroalgal communities, which might have consequences for higher trophic levels. The effects of UVR and grazers on the subtidal community and a comparison of both field experiments are presented by Campana et al.

Growth of several green and red algae was consistently enhanced under high CO2 conditions, but was statistically different only in the intertidal green alga Ulva lactuca and in the red alga Chondrus crispus only under elevated temperatures. The corresponding photosynthetic rates exhibited the same trend, but differences were insignificant. The two brown algae Fucus vesiculosus and Laminaria hyperborea showed opposite responsestowards CO2 increase: While Laminaria hyperborea enhanced growth andphotosynthesis under elevated CO2 conditions, Fucus vesiculosus unexpectedly had lower growth and photosynthesis rates under this condition.The elemental composition (C/N/P) of Fucus vesiculosus in different CO2 conditions did not change and thus no changes in the nutritional quality of the brown seaweed were detected. Accordingly, there were noimplications for the common mesoherbivore Idotea baltica. The isopod feeding on algae from different CO2 treatments did not show differences in food consumption and respiration rates.