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: 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: Marine biological invasions can have alarming and devastating ecological and economic, impacts on biodiversity, ecosystem balance, fisheries and tourism. Due to global change, the number of bioinvasions has severely increased over the last decades. Although, range expansion and the invasion of non-native habitats by marine and terrestrial species have occurred naturally since the existence of life, the rate of human-mediated translocations of species as a consequence of expanded worldwide trade, shipping and aquaculture activities has, however, never been larger and will further massively increase in the near future. For the marine environment, it is estimated that, only in ballast water of ships, approximately 10,000 species per day are transported around the globe. Most of these potential invaders fail, but a few survive, establish and spread in their new environment. To control and prevent invasions, it is of high importance to understand the mechanisms and traits determining the success of invasive species. One of the crucial factors, especially in the early stages of an invasion process, is stress tolerance i.e. the ability to maintain fitness under adverse conditions. Studies comparing the performance of invasive species in their invasive range to native species showed that the invasive species performed better in the majority of cases. In this case, stress tolerance can be considered a species-specific trait. Additionally, some studies comparing the performance of native and invasive populations of the same species were conducted with terrestrial plants and revealed higher competiveness in the invasive plant populations. The marine environment however seems to be nearly unexplored with regard to worldwide intraspecific comparisons of stress tolerance. The aim of this study is to compare the performance of native and invasive populations of successful marine invaders under different abiotic stressors. Laboratory experiments with three marine benthic cosmopolitan invaders in four different biogeographic regions were conducted to detect possible differences in stress tolerance between native and invasive populations. Native and invasive populations of adults and juvenile Pacific oysters, Crassostrea gigas, were exposed to hypoxia and heat stress. Juveniles were additionally exposed to hyposalinity stress. Furthermore, a native and invasive population of the vase tunicate, Ciona intestinalis, were exposed to hypoxia and heat stress and native as well as invasive populations of the green alga, Codium fragile, were exposed to heat and hyposalinity stress. Survival (C. gigas, C. intestinalis) or the 6 maximum quantum yield (C. fragile) under stressful conditions was measured and the native and invasive populations of each species were compared. A second experiment attempted to detect effects of stress history. It was tested whether previously stressed groups of Crassostrea gigas or Ciona intestinalis were more stress tolerant towards a subsequent stressor of another quality than previously unstressed groups. The stress history experiment revealed no significant differences between previously stressed and previously unstressed individuals within both species. Invasive populations of adult Crassostrea gigas from the German Wadden Sea as well as juveniles from Guernsey were significantly more tolerant to hypoxia stress (1 mg l-1) than the native population from Japan. An invasive Japanese population of Ciona intestinalis was significantly more tolerant towards hypoxia stress when compared to the native population from Wales. The same pattern was found for Codium fragile comparing invasive (Chile) and native populations (Japan) under heat stress while under hyposalinity stress an inverse pattern was revealed. The native population (Japan) of juvenile of C. gigas was also more tolerant towards heat stress than its invasive population from Guernsey. Insignificant bidirectional differences in stress tolerance were found between the native (Japan) and invasive (USA) populations of juvenile C. gigas in hyposaline and hypoxic conditions. This study shows, in four out of six significant comparisons, higher stress tolerance is found in invasive populations compared to native populations of the same species. Hence, stress tolerance should not only be considered species-specific but also a population-specific trait. These population-specific differences can be either a consequence of selection of stress-tolerant genotypes during transport or of interactions with the biotic and abiotic environment in the target area after introduction.

Description: Ocean acidification and global warming are known as two of the most crucial factors impacting marine ecosystems worldwide. While most investigations tested short-term impacts of single environmental drivers (e.g. temperature, salintiy) on single species, studies on the combined effect of multiple drivers on a multi-species assemblage in different seasons, which is much more realistic and relevant, are still scarce. Therefore, an experimental mesocosm facility was built to gain information on community changes under the impacts from multiple drivers. In three consecutive experiments, in spring, summer and autumn 2014, compartments of an intertidal macroalgae-mussel community from the Wadden Sea were incubated for 8 to 11 weeks within a large-scale mesocosm facility (Sylt Benthic Mesocosm). In the experiments four different treatments were applied: Ambient, nutrient enrichment (N; doubled natural summer nutrient concentration), warming in combination with acidification (OAW; ambient + 5°C and 1000ppm), and a combination of all three drivers (OAW+N). To find seasonal effects, we compared the responses of (OAW) to that of the ambient treatment in spring, summer and autumn. Carbon flows within the food web of the enclosed species assemblage were analysed by a holistic, static modelling approach (Ecological Network Analysis, ENA). The combined effects of ocean warming and acidification decreased the biomass of the main grazers and the macrophyte Fucus vesiculosus, while epiphytes massively increased due to an altered top-down control during summer. This creates a bottle neck within the energy flow between the first two trophic levels and let less energy pass to higher trophic levels. Enriched nutrients alone did not affect the system substantially, but especially grazers seem to benefit from enriched nutrient concentrations. The effects of climate change on the investigated Wadden Sea community strongly depends on the investigated season. In spring and autumn, OAW affected less or even promoted the system by increased energy flows between the trophic levels. In summer the opposite was found, with decreased energy flow, hampered top-down control and a reduced trophic efficiency, that could propagate through the whole food web and alter the structure and functioning of the investigated community. The Analysis ENA showed a lower relative ascendancy and the trend to an increasing flow diversity, as the result of a high number of multiple pathways between the system components. Theoretically, the resilience of the system shows a tendency to increase and the capability of withstanding external disturbances under OAW as compared to an unstressed system.