ALBERT

Description: Ocean acidification (OA) is generally assumed to negatively impact calcification rates of marine organisms. At a local scale however, biological activity of macrophytes may generate pH fluctuations with rates of change that are orders of magnitude larger than the long-term trend predicted for the open ocean. These fluctuations may in turn impact benthic calcifiers in the vicinity. Combining laboratory, mesocosm and field studies, such interactions between OA, the brown alga Fucus vesiculosus, the sea grass Zostera marina and the blue mussel Mytilus edulis were investigated at spatial scales from decimetres to 100s of meters in the western Baltic. Macrophytes increased the overall mean pH of the habitat by up to 0.3 units relative to macrophyte-free, but otherwise similar, habitats and imposed diurnal pH fluctuations with amplitudes ranging from 0.3 to more than 1 pH unit. These amplitudes and their impact on mussel calcification tended to increase with increasing macrophyte biomass to bulk water ratio. At the laboratory and mesocosm scales, biogenic pH fluctuations allowed mussels to maintain calcification even under acidified conditions by shifting most of their calcification activity into the daytime when biogenic fluctuations caused by macrophyte activity offered temporal refuge from OA stress. In natural habitats with a low biomass to water body ratio, the impact of biogenic pH fluctuations on mean calcification rates of M. edulis was less pronounced. Thus, in dense algae or seagrass habitats, macrophytes may mitigate OA impact on mussel calcification by raising mean pH and providing temporal refuge from acidification stress.

Description: Coastal areas are subject to multiple stressors generated by human activities on land and at sea. Combined effects of multiple stressors on marine biota may be very complex and cannot easily be predicted from individual stressor effects. Among the anthropogenic threats to the coastal environment, accumulation of plastic waste in the ocean has recently caught public attention. Small plastic particles(〈 5 mm), so-called microplastics, can adversely affect the physiology of marine inve1iebrates. Filter-feeding organisms in particular may be impaired because they ingest microplastics while feeding. Ocean warming due to ongoing greenhouse gas emissions constitutes another known stressor for marine ecosystems. As warming has a strong influence on metabolic rates in ectothermic invetiebrates, we hypothesized that the effect size of a response induced by the microplastic patiicles changes with increasing temperature. We exposed the Azorean barnacle Megabalanus azoricus from Madeira Island to an 01ihogonal combination of three temperature levels (22°C, 25°C, 28°C) and four microplastic concentrations (0 mg 1-1, 2 mg 1-1, 20 mg 1-1, 200 mg 1-1) for 69 days. Moulting frequency, cirral activity, respiration rates and m01iality served as response variables to assess individual and combined effects of temperature and microplastic. Our study demonstrated that M azoricus ingests as well as excretes microplastic particles. Warming significantly increased motiality and moulting frequency and induced changes in cirral beating behaviour of the barnacles. Microplastic alone did not have an effect on any of the measured response variables. Contrary to expectations, we found the highest survival rate in the group of the highest microplastic concentration, whereas the group without microplastic featured the lowest survival rate. Furthermore, we found a significant interaction of microplastic and warming with regard to extended cirral beating behaviour. Repeated measures of respiration rate and total cirral beating rate indicated a strong effect of time kept in the laboratory on the barnacles. Detailed analysis of our results revealed that the dominant stressor driving the magnitude of all observed effects was presumably food availability. Insufficient food supply over the course of the experiment may have led to energy depletion, which induced a considerable decrease of respiration rates and total cirral beating rates. Elevated water temperature, the second most influential stressor in the experiment, increased metabolic rates and by association moulting frequency of the barnacles. High metabolic rates may have forced the animals to consume their energy reserves even faster, which presumably caused increased mortality at higher temperature. Since we did not find individual effects of microplastic on M azor;cus, we were unfo1tunately not able to test our core hypothesis. Nevertheless, we found evidence that high concentrations of microplastic in combination with elevated temperature may elicit changes in metabolic activity of M azo,•;cus either caused by pseudo-satiation or in the wake of a protective mechanism. Our results would seem to suggest that ocean warming poses a larger risk to M azoricus than microplastic particles. Moreover, as adult M azoricus appeared to be rather unaffected by microplastic, the present study also highlights the need to investigate whether effects of microplastics on organisms differ from effects of naturally occurring non-nutritious particles in seston.

Description: Ocean acidification (OA) is generally assumed to negatively impact calcification rates of marine organisms. At a local scale however, biological activity of macrophytes may generate pH fluctuations with rates of change that are orders of magnitude larger than the long-term trend predicted for the open ocean. These fluctuations may in turn impact benthic calcifiers in the vicinity. Combining laboratory, mesocosm and field studies, such interactions between OA, the brown alga Fucus vesiculosus, the sea grass Zostera marina and the blue mussel Mytilus edulis were investigated at spatial scales from decimetres to 100s of meters in the western Baltic. Macrophytes increased the overall mean pH of the habitat by up to 0.3 units relative to macrophyte- free, but otherwise similar, habitats and imposed diurnal pH fluctuations with amplitudes ranging from 0.3 to more than 1 pH unit. These amplitudes and their impact on mussel calcification tended to increase with increasing macrophyte biomass to bulk water ratio. At the laboratory and mesocosm scales, biogenic pH fluc- tuations allowed mussels to maintain calcification even under acidified conditions by shifting most of their calcification activity into the daytime when biogenic fluctuations caused by macrophyte activity offered temporal refuge from OA stress. In natural habitats with a low biomass to water body ratio, the impact of biogenic pH fluctuations on mean calcification rates of M. edulis was less pronounced. Thus, in dense algae or seagrass habitats, macrophytes may mitigate OA impact on mussel calcification by raising mean pH and providing temporal refuge from acidification stress.

Description: Salinity, oxygen and pH conditions in the microhabitat patches of Fucus, Zostera and sand at daytime and nighttime in the months august and september 2013 as sampled by regular SCUBA dives.

Description: A transect from the rim to the inner part of a Fucus stand was simulated by connecting 5 aquaria (replicated 3 times) in a series with 1 Fucus individual in each aquaria except the first. Thus the water chemistry in the successive aquaria reflected the presence and metabolism of 0, 1, 2, 3, and 4 Fucus individuals “upstream”. The water flowing through each series stemmed from a header tank which was either acidified or not.

Description: Calcification rate of mussels in water from different distances from the rim into natural (in situ) and simulated (aquarium series) Fucus stands was assessed under daytime and nighttime conditions.

Description: Daily mean and amplitude of pH assessed under acidified and non-acidified conditions in the natural and simulated transects into a Fucus patch and in the 3 different microhabitats in situ.

Description: Ocean acidification (OA) is generally assumed to negatively impact calcification rates of marine organisms. At a local scale however, biological activity of macrophytes may generate pH fluctuations with rates of change that are orders of magnitude larger than the long-term trend predicted for the open ocean. These fluctuations may in turn impact benthic calcifiers in the vicinity. Combining laboratory, mesocosm and field studies, such interactions between OA, the brown alga Fucus vesiculosus, the sea grass Zostera marina and the blue mussel Mytilus edulis were investigated at spatial scales from decimetres to 100s of meters in the western Baltic. Macrophytes increased the overall mean pH of the habitat by up to 0.3 units relative to macrophyte- free, but otherwise similar, habitats and imposed diurnal pH fluctuations with amplitudes ranging from 0.3 to more than 1 pH unit. These amplitudes and their impact on mussel calcification tended to increase with increasing macrophyte biomass to bulk water ratio. At the laboratory and mesocosm scales, biogenic pH fluc- tuations allowed mussels to maintain calcification even under acidified conditions by shifting most of their calcification activity into the daytime when biogenic fluctuations caused by macrophyte activity offered temporal refuge from OA stress. In natural habitats with a low biomass to water body ratio, the impact of biogenic pH fluctuations on mean calcification rates of M. edulis was less pronounced. Thus, in dense algae or seagrass habitats, macrophytes may mitigate OA impact on mussel calcification by raising mean pH and providing temporal refuge from acidification stress.