Angelika Graiff

Season exerts differential effects of ocean acidification and warming on growth and carbon metabolism of the seaweed Fucus vesiculosus in the western Baltic Sea

Warming and acidification of the oceans as a consequence of increasing CO2-concentrations occur at large scales. Numerous studies have shown the impact of single stressors on individual species. However, studies on the combined effect of multiple stressors on a multi-species assemblage, which is ecologically much more realistic and relevant, are still scarce. Therefore, we orthogonally crossed the two factors warming and acidification in mesocosm experiments and studied their single and combined impact on the brown alga Fucus vesiculosus associated with its natural community (epiphytes and mesograzers) in the Baltic Sea in all seasons (from April 2013 to April 2014). We superimposed our treatment factors onto the natural fluctuations of all environmental variables present in the Benthocosms in so-called delta-treatments. Thereby we compared the physiological responses of F. vesiculosus (growth and metabolites) to the single and combined effects of natural Kiel Fjord temperatures and pCO2 conditions with a 5 °C temperature increase and/or pCO2 increase treatment (1100 ppm in the headspace above the mesocosms). Responses were also related to the factor photoperiod which changes over the course of the year. Our results demonstrate complex seasonal pattern. Elevated pCO2 positively affected growth of F. vesiculosus alone and/or interactively with warming. The response direction (additive, synergistic or antagonistic), however, depended on season and daylength. The effects were most obvious when plants were actively growing during spring and early summer. Our study revealed for the first time that it is crucial to always consider the impact of variable environmental conditions throughout all seasons. In summary, our study indicates that in future F. vesiculosus will be more affected by detrimental summer heat-waves than by ocean acidification although the latter consequently enhances growth throughout the year. The mainly negative influence of rising temperatures on the physiology of this keystone macroalga may alter and/or hamper its ecological functions in the shallow coastal ecosystem of the Baltic Sea.

Restructuring of Epibacterial Communities on Fucus vesiculosus forma mytili in Response to Elevated pCO2 and Increased Temperature Levels

Marine multicellular organisms in composition with their associated microbiota—representing metaorganisms—are confronted with constantly changing environmental conditions. In 2110, the seawater temperature is predicted to be increased by ~5°C, and the atmospheric carbon dioxide partial pressure (pCO2) is expected to reach approximately 1000 ppm. In order to assess the response of marine metaorganisms to global changes, e.g., by effects on host-microbe interactions, we evaluated the response of epibacterial communities associated with Fucus vesiculosus forma mytili (F. mytili) to future climate conditions. During an 11-week lasting mesocosm experiment on the island of Sylt (Germany) in spring 2014, North Sea F. mytili individuals were exposed to elevated pCO2 (1000 ppm) and increased temperature levels (Δ+5°C). Both abiotic factors were tested for single and combined effects on the epibacterial community composition over time, with three replicates per treatment. The respective community structures of bacterial consortia associated to the surface of F. mytili were analyzed by Illumina MiSeq 16S rDNA amplicon sequencing after 0, 4, 8, and 11 weeks of treatment (in total 96 samples). The results demonstrated that the epibacterial community structure was strongly affected by temperature, but only weakly by elevated pCO2. No interaction effect of both factors was observed in the combined treatment. We identified several indicator operational taxonomic units (iOTUs) that were strongly influenced by the respective experimental factors. An OTU association network analysis revealed that relationships between OTUs were mainly governed by habitat. Overall, this study contributes to a better understanding of how epibacterial communities associated with F. mytili may adapt to future changes in seawater acidity and temperature, ultimately with potential consequences for host-microbe interactions.

Seasonal variations of Fucus vesiculosus fertility under ocean acidification and warming in the western Baltic Sea

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

Buffering and Amplifying Interactions among OAW (Ocean Acidification & Warming) and Nutrient Enrichment on Early Life-Stage Fucus vesiculosus L. (Phaeophyceae) and Their Carry Over Effects to Hypoxia Impact

Ocean acidification and warming (OAW) are occurring globally. Additionally, at a more local scale the spreading of hypoxic conditions is promoted by eutrophication and warming. In the semi-enclosed brackish Baltic Sea, occasional upwelling in late summer and autumn may expose even shallow-water communities including the macroalga Fucus vesiculosus to particularly acidified, nutrient-rich and oxygen-poor water bodies. During summer 2014 (July–September) sibling groups of early life-stage F. vesiculosus were exposed to OAW in the presence and absence of enhanced nutrient levels and, subsequently to a single upwelling event in a near-natural scenario which included all environmental fluctuations in the Kiel Fjord, southwestern Baltic Sea, Germany (54°27 ´N, 10°11 ´W). We strove to elucidate the single and combined impacts of these potential stressors, and how stress sensitivity varies among genetically different sibling groups. Enhanced by a circumstantial natural heat wave, warming and acidification increased mortalities and reduced growth in F. vesiculosus germlings. This impact, however, was mitigated by enhanced nutrient conditions. Survival under OAW conditions strongly varied among sibling groups hinting at a substantial adaptive potential of the natural Fucus populations in the Western Baltic. A three-day experimental upwelling caused severe mortality of Fucus germlings, which was substantially more severe in those sibling groups which previously had been exposed to OAW. Our results show that global (OAW), regional (nutrient enrichment) and local pressures (upwelling), both alone and co-occurring may have synergistic and antagonistic effects on survival and/or growth of Fucus germlings. This result emphasizes the need to consider combined stress effects.

Effects of warming and acidification on a benthic community in the Baltic Sea - Kiel Benthocosms

Station Biologique de Roscoff, Sorbonne Universités, Université Pierre et Marie Curie, CNRS, Roscoff 29688, France; Institut de Systématique, Evolution, Biodiversité, UMR 7205CNRS-EPHE-MNHN-UPMC, Muséum National d’Histoire Naturelle, Paris 75231, France; Station Biologique de Roscoff, CNRS, Sorbonne Universités, Université Pierre et Marie Curie, Roscoff 29688, France and Station Biologique de Roscoff, CNRS, Sorbonne Universités, Université Pierre et Marie Curie, Roscoff 29688, FranceEarly life-stage of the bladderwrack Fucus vesiculosus is highly influenced by the climate change factors temperature, CO2 and eutrophication. Intraspecific genetic diversity of Baltic Fucus vesiculosus populations is low, compared to e.g. Atlantic populations, which may limit their potential for adaptation. To assess the role of intraspecific genetic diversity on the tolerance towards environmental change we manipulated their diversity: Plots with full-sibling Keynote and Oral Papers 106 Downloaded by [University of Kiel] at 02:13 22 September 2015 groups of Fucus germlings each originating from one parental pair represents the low diversity level, whereas plots with sibling groups from multiple parental pairs represent the high diversity level. Climate change was simulated according to the year 2100 in the near-natural scenario Kiel Benthocosms by maintaining the environmental fluctuations of the Baltic Sea and adding 5°C warming, 600 μatm pCO2 and doubling the nutrient concentrations. Germlings responded to warming with higher mortality and enhanced growth rates. High pCO2 concentrations increased growth due to a fertilisation effect. Nonphotochemical quenching was lower under warmed than ambient temperatures. A positive co-tolerance among sibling groups towards warming and acidification indicates the possible attenuation in presence of the multiple factors. Considerable differences among sibling group performance indicate a higher adaptive potential for genetically diverse populations. The high diversity levels also showed higher survival, indicating possible facilitation processes among genotypes. Microsatellite genotyping is in progress for revealing whether and how selection processes took place in high diversity levels. We conclude that impacts on early life-stage bladderwrack depend on the combination of stressors and season and that genetic variation is crucial for local adaptation to climate change stress

Tolerance to climate change of early life-stage Fucus Vesiculosus varies among sibling groups

Station Biologique de Roscoff, Sorbonne Universités, Université Pierre et Marie Curie, CNRS, Roscoff 29688, France; Institut de Systématique, Evolution, Biodiversité, UMR 7205CNRS-EPHE-MNHN-UPMC, Muséum National d’Histoire Naturelle, Paris 75231, France; Station Biologique de Roscoff, CNRS, Sorbonne Universités, Université Pierre et Marie Curie, Roscoff 29688, France and Station Biologique de Roscoff, CNRS, Sorbonne Universités, Université Pierre et Marie Curie, Roscoff 29688, FranceEarly life-stage of the bladderwrack Fucus vesiculosus is highly influenced by the climate change factors temperature, CO2 and eutrophication. Intraspecific genetic diversity of Baltic Fucus vesiculosus populations is low, compared to e.g. Atlantic populations, which may limit their potential for adaptation. To assess the role of intraspecific genetic diversity on the tolerance towards environmental change we manipulated their diversity: Plots with full-sibling Keynote and Oral Papers 106 Downloaded by [University of Kiel] at 02:13 22 September 2015 groups of Fucus germlings each originating from one parental pair represents the low diversity level, whereas plots with sibling groups from multiple parental pairs represent the high diversity level. Climate change was simulated according to the year 2100 in the near-natural scenario Kiel Benthocosms by maintaining the environmental fluctuations of the Baltic Sea and adding 5°C warming, 600 μatm pCO2 and doubling the nutrient concentrations. Germlings responded to warming with higher mortality and enhanced growth rates. High pCO2 concentrations increased growth due to a fertilisation effect. Nonphotochemical quenching was lower under warmed than ambient temperatures. A positive co-tolerance among sibling groups towards warming and acidification indicates the possible attenuation in presence of the multiple factors. Considerable differences among sibling group performance indicate a higher adaptive potential for genetically diverse populations. The high diversity levels also showed higher survival, indicating possible facilitation processes among genotypes. Microsatellite genotyping is in progress for revealing whether and how selection processes took place in high diversity levels. We conclude that impacts on early life-stage bladderwrack depend on the combination of stressors and season and that genetic variation is crucial for local adaptation to climate change stress