ALBERT

Description: Climate change research is advancing to more complex and more comprehensive studies that include long-term experiments, multiple life-history stages, multi-population, and multi-trait approaches. We used a population of the barnacle Balanus improvisus known to be sensitive to short-term acidification to determine its potential for long-term acclimation to acidification. We reared laboratory-bred individuals (as singles or pairs), and field-collected assemblages of barnacles, at pH 8.1 and 7.5 ( 400 and 1600 ?atm pCO2 respectively) for up to 16 months. Acidification caused strong mortality and reduced growth rates. Acidification suppressed respiration rates and induced a higher feeding activity of barnacles after 6 months, but this suppression of respiration rate was absent after 15 months. Laboratory-bred barnacles developed mature gonads only when they were held in pairs, but nonetheless failed to produce fertilized embryos. Field-collected barnacles reared in the laboratory for 8 months at the same pH’s developed mature gonads, but only those in pH 8.1 produced viable embryos and larvae. Because survivors of long-term acidification were not capable of reproducing, this demonstrates that B. improvisus can only partially acclimate to long-term acidification. This represents a clear and significant bottleneck in the ontogeny of this barnacle population that may limit its potential to persist in a future ocean.

Description: Climate change research is advancing to more complex and more comprehensive studies that include long-term experiments, multiple life-history stages, multi-population, and multi-trait approaches. We used a population of the barnacle Balanus improvisus known to be sensitive to short-term acidification to determine its potential for long-term acclimation to acidification. We reared laboratory-bred individuals (as singles or pairs), and field-collected assemblages of barnacles, at pH 8.1 and 7.5 (400 and 1600 μatm pCO2 respectively) for up to 16 months. Acidification caused strong mortality and reduced growth rates. Acidification suppressed respiration rates and induced a higher feeding activity of barnacles after 6 months, but this suppression of respiration rate was absent after 15 months. Laboratory-bred barnacles developed mature gonads only when they were held in pairs, but nonetheless failed to produce fertilized embryos. Field-collected barnacles reared in the laboratory for 8 months at the same pH's developed mature gonads, but only those in pH 8.1 produced viable embryos and larvae. Because survivors of long-term acidification were not capable of reproducing, this demonstrates that B. improvisus can only partially acclimate to long-term acidification. This represents a clear and significant bottleneck in the ontogeny of this barnacle population that may limit its potential to persist in a future ocean.

Description: Increasing human activities cause local to global changes in sea surface temperatures, ocean acidity, eutrophication, and rising sea levels. Many laboratory experiments investigate the effects of these regime shifts on single species and single stressors, showing variable responses within and among species, while different combinations of stressors can have synergistic, additive or antagonistic effects. Large-scale multi-species and multi-stressor experiments can more reliably predict future ecosystem changes. A unique mesocosm facility was developed and set up at the AWI Wadden Sea Station – Sylt, Northern Germany to investigate the particular effects of future climate changes on predominant marine intertidal communities. Each of 12 benthic mesocosms serves as an independent experimental unit with novel techniques of tide and current simulations as well as multi parameter measurement systems to simulate multi-factorial climate change scenarios including the combination of warming, acidification, nutrient enrichment, and sea level rise. Temperature, pH, oxygen, and salinity can be continuously monitored and logged, while discretely collected samples of total alkalinity, light availability, chlorophyll a (Chl a ), nutrients and seston supplement these online datasets. Herein we demonstrate the functionality of the new benthic mesocosm system including first experimental results on the responses of Fucus vesiculosus forma mytili , and its associated community to the combination of warming, ocean acidification, and increased nutrient enrichment.

Description: Impact of simulated marine heatwaves on foundation macrophytes in the Baltic Sea. Abstract Marine heatwaves have been observed worldwide and are expected to increase in both frequency and intensity due to climate change. Such events may cause ecosystem reconfigurations arising from species range contraction or redistribution, with ecological, economic and social implications. Macrophytes such as the brown seaweed Fucus vesiculosus and the seagrass Zostera marina are foundation species in many coastal ecosystems of the temperate northern hemisphere. Hence, their response to extreme events can potentially determine the fate of associated ecosystems. Macrophyte functioning is intimately linked to the maintenance of photosynthesis, growth and reproduction, and resistance against pathogens, epibionts and grazers. We investigated morphological, physiological, pathological and chemical defence responses of western Baltic Sea F. vesiculosus and Z. marina populations to simulated near‐natural marine heatwaves. Along with (a) the control, which constituted no heatwave but natural stochastic temperature variability (0HW), two treatments were applied: (b) two late‐spring heatwaves (June, July) followed by a summer heatwave (August; 3HW) and (c) a summer heatwave only (1HW). The 3HW treatment was applied to test whether preconditioning events can modulate the potential sensitivity to the summer heatwave. Despite the variety of responses measured in both species, only Z. marina growth was impaired by the accumulative heat stress imposed by the 3HW treatment. Photosynthetic rate, however, remained high after the last heatwave indicating potential for recovery. Only epibacterial abundance was significantly affected in F. vesiculosus. Hence both macrophytes, and in particular F. vesiculosus, seem to be fairly tolerant to short‐term marine heatwaves at least at the intensities applied in this experiment (up to 5°C above mean temperature over a period of 9 days). This may partly be due to the fact that F. vesiculosus grows in a highly variable environment, and may have a high phenotypic plasticity.

Description: Abstract Climate change will shift mean environmental conditions and also increase the frequency and intensity of extreme events, exerting additional stress on ecosystems. While field observations on extremes are emerging, experimental evidence of their biological consequences is rare. Here, we introduce a mesocosm system that was developed to study the effects of environmental variability of multiple drivers (temperature, salinity, pH, light) on single species and communities at various temporal scales (diurnal ‐ seasonal): the Kiel Indoor Benthocosms (KIBs). Both, real‐time offsets from field measurements or various dynamic regimes of environmental scenarios, can be implemented, including sinusoidal curve functions at any chosen amplitude or frequency, stochastic regimes matching in situ dynamics of previous years and modeled extreme events. With temperature as the driver in focus, we highlight the strengths and discuss limitations of the system. In addition, we examined the effects of different sinusoidal temperature fluctuation frequencies on mytilid mussel performance. High‐frequency fluctuations around a warming mean (+2°C warming, ± 2°C fluctuations, wavelength = 1.5 d) increased mussel growth as did a constant warming of 2°C. Fluctuations at a lower frequency (+2 and ± 2°C, wavelength = 4.5 d), however, reduced the mussels’ growth. This shows that environmental fluctuations, and importantly their associated characteristics (such as frequency), can mediate the strength of global change impacts on a key marine species. The here presented mesocosm system can help to overcome a major short‐coming of marine experimental ecology and will provide more robust data for the prediction of shifts in ecosystem structure and services in a changing and fluctuating world.

Description: Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless in many coastal areas high p CO 2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg -1 ) and CO 2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual p CO 2 variability in this habitat and the combined effects of elevated p CO 2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of p CO 2 up to 3350 μatm. Kiel Fjord was characterized by strong seasonal p CO 2 variability. During summer, maximal p CO 2 values of 2500 μatm were observed at the surface and 〉3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high p CO 2 inner fjord field station (mean p CO 2 ca. 1000 μatm) in comparison to a low p CO 2 outer fjord station (ca. 600 μatm). In addition, mussels were able to outcompete the barnacle Amphibalanus improvisus at the high p CO 2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater p CO 2 . At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus . We conclude that benthic stages of M. edulis tolerate high ambient p CO 2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification. © 2012 Blackwell Publishing Ltd