Beschreibung: The Kiel Outdoor Benthocosm infrastructure (Kiel, Germany,N 54°19.8'; E 010°09.0') allows combining natural in-situ fluctuations on all environmental variables with the controlled manipulation of treatment factors. The environmental fluctuations are admitted by a continuous flow-through of fjord water. The treatment is applied by delta-treatments which shift the mean of target variables (temperature and pH in this case) while maintaining the frequency and amplitude of natural fluctuations. The data presented here show the treatment levels and the continuously logged temperature and pH conditions in the experimental tanks. The dynamics of temperature and pH are driven by (i) in situ variability, (ii) the treatments imposed and (iii) the biology of the biota in the tanks. These contained macroalgal communities with associated mesograzers, mussels, and sea stars. The data set comprised 5 experimental runs: spring experiment (4.4.-19.6.2013), summer experiment 1 (4.7.-17.9.2013), autumn experiment (10.10-17.12.2013), winter experiment (16.1. - 1.4.2014), summer experiment 2 (10.7. - 26.9.2014).

Beschreibung: Laboratory experiments were performed measuring calcification rates in Baltic Sea mussel at various salintiies, bicarbonate and calcium ion concentrations. Predictors of calcification were calculated and correlated with calcification rates. Field monitoring of carbonate chemistry, salinity and temperature was conducted and correlated with field calcification rates in southwest Baltic Sea mussel reefs.

Beschreibung: This data set presents data from further 1.5 month-long laboratory experiments conducted at GEOMAR in Kiel, Germany where calcium ion concentration in seawater was manipulated to investigate how seawater calcium availability controls calcification in Baltic Sea Mytilus edulis trossulus mussels. Calcification rates (mass of calcium carbonate produced per unit time) was measured in 4 replicate tanks across 3 salinities and 5 calcium ion concentrations to estimate the concentration at which calcium ions start to limit calcification in the Baltic Sea at low salinities.

Beschreibung: This data set presents data from field monitoring of calcification rates across 15 months from 3 sites in the South-West Baltic Sea (Kiel fjord, Ahrenshoop and Usedom Island). 50 mussels were sampled from settlement structures at each location at 2 - 3 monthly intervals and shell length/mass were recorded over time to estimate calcification rates in the field related to environmental conditions.

Beschreibung: This data set presents data from 2 month-long laboratory experiments conducted at GEOMAR, Kiel (Germany) where seawater bicarbonate ion concentrations were manipulated to investigate the effects of limited seawater carbon availability on calcification rates in juvenile Baltic Sea Mytilus edulis trossulus. Calcification rates (mass of calcium carbonate produced per unit time) was measured in 4 replicate tanks across 3 salinities and 5 bicarbonate ion concentrations to estimate the concentration at which bicarbonate ions start to limit calcification in the Baltic Sea at low salinities.

Beschreibung: This data set is a combination of data from both laboratory experiments where carbonate chemistry parameters from both were used to calculate aragonite saturation state (omega) and the extended calcification substrate inhibitor ratio (ESIR). These mean values from each experimental treatment are plotted with mean values for calcification in each experimental treatment from both experiments to understand whether omega or ESIR can predict calcification more accurately in the Baltic Sea and whether Baltic Sea mussels can cope with lower ESIR and Omega values than fully marine populations.

Beschreibung: This data set presents data from environmental coastal monitoring of carbonate chemistry parameters at the same 3 sites in the Baltic Sea over the course of 2 years. Poisoned water samples were analysed in laboratories in GEOMAR, Kiel and IOW, Rostock to understand the variation in carbonate chemistry and salinity and how this correlates with calcification rates of mussels in the field. These carbonate chemistry parameters were used to calculate aragonite saturation state (omega) and the ratio of calcification substrate to inhibitor (ESIR) to describe the environmental conditions relevant for calcification along the Baltic Sea salinity gradient.

Beschreibung: This data set presents data from parallel environmental monitoring from the same 3 Baltic Sea sites using Star-Oddi mini CTD loggers. Salinity data was converted to calcium ion concentrations using published conversion factors for the Baltic Sea. This monitoring was implemented to understand natural levels of seawater calcium in South-West Baltic mussel reefs and how this impacts calcification.

Beschreibung: 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.

Beschreibung: 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.