ALBERT

Description: Baltic blue mussels colonise and dominate benthic habitats with much lower salinity than any other marine mytilid population globally. Surprisingly, all Baltic populations are hybrids of Mytilus edulis x M. trossulus genotypes with the former dominating hybrid genotypes in the western (high salinity) and the latter in the eastern part of the Baltic (low salinity). Here, we tested if low salinity selects for M. trossulus dominated hybrid genotypes and whether populations along the salinity gradient are locally adapted to their specific salinity regimes. Using laboratory larval rearing trials, we can show that Baltic M. trossulus hybrids have higher fitness when exposed to salinities 〈10 psu whereas Baltic M. edulis hybrids have higher fitness at a salinity of 16 psu. In addition, we can demonstrate that populations from the centre of the hybrid cline can be selected towards Baltic M. trossulus hybrids at low salinities, with allele shifts significantly beyond genetic drift expectations. We conclude that salinity driven selection can shape mussel populations and hence allows for local adaptation to extremely low environmental salinity. Future climate change driven desalination therefore has the potential to shift the Baltic Sea hybrid gradient to the west, with important implications for ecology and aquaculture.

Description: Experiments were performed to test the effect of seawater [Ca2+] on the formation rate of the larval prodissoconch I shell in 'Baltic mussels in combination with modified carbonate chemistry. In addition, [Ca2+] of the extrapallial fluid were measured in depdendency of the seawater [Ca2+]. These experimental data were correlated with the [Ca2+] present in the Baltic Sea.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: Climate change is predicted to alter salinity in many coastal regions. This exerts significant physiological stress on coastal invertebrates whose body fluid osmolality follows that of seawater ('osmoconformers'). Osmolytes are the cellular actors in osmoconformers that regulate acclimation to salinity changes. Inspite of their cellular importance in salinity tolerance, cellular volume regulation and its osmotic components, are not sufficiently understood. Which compounds are commonly used as osmolytes? Are inorganic and organic osmolytes used in long-term salinity acclimation? Are there taxonomic- or tissue specific differences? By conducting an extensive literature search, this study aimed to answer these questions. By using a meta-analysis approach over an ordinary literature review we were able to statistically evaluate the individual effect sizes by computing a summary effect for multiple studies to estimate the mean of the distribution of the true effect sizes. Meta-analysis is useful to reveal research gaps, common actors across taxa, or overall effects of biotic factors. We thus conducted a systematic review and meta-analysis of osmolyte data (both organic and inorganic) utilized by osmoconforming marine invertebrates during a 〉14-day acclimation to reduced salinity. This study offers a valuable overview of the various listed organic compounds across species and whether and in which organisms they are used as osmolytes under low salinity stress. This study thereby creates a valuable baseline for future research. 2389 studies were screened according to standard systematic review procedures (title scan, abstract scan and full-exam) resulting a total of 56 studies that fulfilled the search criteria. The data includes the list of all papers that underwent a full-exam in the systematic review process and passed the search criteria and study details of the studies used for meta-analysis. For all included studies the input data necessary to conduct a meta-analysis with a hedge's g effect size is given. Namely, mean osmolyte concentrations, variance measure and replicate numbers are given for the high and low salinity treatment. The data for any benthic osmoconforming species and any osmolyte type is included. The data table is sorted by study but gives additional information on taxonomy, experimental details, study design, osmolyte type, tissue type, etc. Additionally, data is available for a number of studies that reported an extensive osmolyte budget (i.e. multiple compounds). Here, for each study and study organism osmolytes (that were present in more than one study) are listed as percent of the total organic osmolyte pool. This dataset is the first systematically compiled list of studies investigating osmolyte concentrations in osmoconformers after long-term (〉14 days) acclimation to low salinity. Data can be used to compare own osmolyte data (species/osmolyte compound) with a comprehensive list of osmolyte literature data. Additionally, this data can be used to address other hypotheses via meta-analysis. As this was a systematic review, no biological samples were collected in this study. Information of the origin of the data from each of the included studies can be found in the list of all included studies.

Description: This table contains a list of studies that report concentrations for multiple organic osmolytes. These concentrations were calculated into proportions of the total organic osmolyte pool and grouped by taxa (shown in figure 8 of Podbielski et al. 2022). If the sum deviates from 100% this may be caused by using the values for total solute given in the respective papers whenever they were reported. Here, slight deviations from 100% maybe due to rounding errors. Larger deviations are likely caused when total solutes and specific osmolytes were quantified with different techniques. For example, total solutes are sometimes determined as Ninhydrine-positive substances or quaternary ammonium compounds. This may include methylamines or other free amino acids which are not determined via targeted techniques to measure amino acids (i.e. via amino acid analyser). The column "Osmolyte, other" combines values for compounds (〈5%) and, if present, values for other compounds, which were data given by the respective papers.

Description: All studies included in the meta-analysis are listed with study details such as experimental design, species studied, number of replicates, salinity levels and mean values and variances of the studied parameters. Data are only reported if full data (replication, mean, variation) were given.