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.

Description: This dataset comprises the physiological and behavioural stress response of the deep pelagic jellyfish Periphylla periphylla to anthropogenic disturbance. Specifically, we tested the effects of ocean warming and sediment plumes from deep-sea mining during ex situ experiments, using Periphylla collected in the Lurefjord and Sognefjord, Norway, in 2021. Measurement outcomes include respiration from fiber optics or through electron transfer system analysis (Bode et al. 2013), ammonium excretion (Holmes et al. 1999) and a health score associated with the response to sediment plumes. Microbial community composition and taxonomy were also investigated and results are published in the related dataset https://doi.org/10.1594/PANGAEA.957395.

Description: This dataset comprises gene expression data in the deep pelagic jellyfish Periphylla periphylla exposed to anthropogenic disturbance. Specifically, we tested the effects of ocean warming and sediment plumes from deep-sea mining during ex situ experiments, using Periphylla collected in the Lurefjord and Sognefjord, Norway, in 2021. Gene expression is given in normalised counts for each expressed transcript (for both the temperature and suspended sediment separately). Moreover, this dataset lists all significantly expressed transcripts and their summary statistics (e.g. log2 fold change), as identified with Likelihood Ratio Tests (LRT) in DESeq2 (Love et al. 2014), in addition to transcript annotations performed with Trinotate v3.2.1 searching the Blastx, Blastp, Pfam, UniProt-SwissProt, GO, eggNOG and KEGG databases (Bryant et al. 2017).

Description: This dataset comprises the microbial community composition associated with the outer bell of the deep pelagic jellyfish Periphylla periphylla exposed to anthropogenic disturbance. Specifically, we tested the effects of ocean warming and sediment plumes from deep-sea mining during ex situ experiments, using Periphylla collected in the Lurefjord and Sognefjord, Norway, in 2021. Microbial community composition is given in raw counts for each amplicon sequence variant (ASV) encountered, based on 16S rRNA sequencing. Taxonomy for each ASV is listed, including Kingdom, Phylum, Class, Order, Family, Genus and Species, which were assigned using QIIME2 and the Silva 132 99% OTUs 16S rRNA database (Quast et al. 2013).

Description: In coastal temperate regions such as the Baltic Sea, calcifying bivalves dominate benthic communities playing a vital ecological role in maintaining biodiversity and nutrient recycling. At low salinities, bivalves exhibit reduced growth and calcification rates which is thought to result from physiological constraints associated with osmotic stress. Calcification demands a considerable amount of energy in calcifying molluscs and estuarine habitats provide sub-optimal conditions for calcification due to low concentrations of calcification substrates and large variations in carbonate chemistry. Therefore, we hypothesize that slow growth rates in estuarine bivalves result from increased costs of calcification, rather than costs associated with osmotic stress. To investigate this, we estimated the cost of calcification for the first time in benthic bivalve life stages and the relative energy allocation to calcification in three Mytilus populations along the Baltic salinity gradient. Our results indicate that calcification rates are significantly reduced only in 6 psu populations compared to 11 and 16 psu populations, coinciding with ca. 2–3-fold higher calcification costs at low salinity and temperature. This suggests that reduced growth of Baltic Mytilus at low salinities results from increased calcification costs rather than osmotic stress related costs. We also reveal that shell growth (both calcification and shell organic production) demands 31–60% of available assimilated energy from food, which is significantly higher than previous estimates. Energetically expensive calcification represents a major constraint on growth of mytilids in the estuarine and coastal seas where warming, acidification and desalination are predicted over the next century.