Beschreibung: This data set comprises laboratory measurements of calcium, pH and carbonate concentrations in seawater and beneath the shell (calcification site) to constrain calcium carbonate saturation state dynamics during calcification in larval mussels, under control and acidified conditions. In addition, data on calcium accumulation (flame photometry) during larval calcification was collected. Finally, shell length growth and shell dissolution data under acidified conditions were also collected. This data was collected by Ramesh et al. (accepted) Nature Communications. Data is organized as it appears in figures in the published manuscript. Fig.3 and 4 data are presented in a single table.

Beschreibung: Experimental ocean acidification leads to a shift in resource allocation and to an increased [HCO3-] within the perivisceral coelomic fluid (PCF) in the Baltic green sea urchin Strongylocentrotus droebachiensis. We investigated putative mechanisms of this pH compensation reaction by evaluating epithelial barrier function and the magnitude of skeleton (stereom) dissolution. In addition, we measured ossicle growth and skeletal stability. Ussing chamber measurements revealed that the intestine formed a barrier for HCO3- and was selective for cation diffusion. In contrast, the peritoneal epithelium was leaky and only formed a barrier for macromolecules. The ossicles of 6 week high CO2-acclimatised sea urchins revealed minor carbonate dissolution, reduced growth but unchanged stability. On the other hand, spines dissolved more severely and were more fragile following acclimatisation to high CO2. Our results indicate that epithelia lining the PCF space contribute to its acid–base regulation. The intestine prevents HCO3- diffusion and thus buffer leakage. In contrast, the leaky peritoneal epithelium allows buffer generation via carbonate dissolution from the surrounding skeletal ossicles. Long-term extracellular acid–base balance must be mediated by active processes, as sea urchins can maintain relatively high extracellular [HCO3-]. The intestinal epithelia are good candidate tissues for this active net import of HCO3- into the PCF. Spines appear to be more vulnerable to ocean acidification which might significantly impact resistance to predation pressure and thus influence fitness of this keystone species.

Beschreibung: The excretion of nitrogenous waste products in the form of ammonia (NH3) and ammonium (NH4+) is a fundamental process in aquatic organisms. For mytilid bivalves little is known about the mechanisms and sites of excretion. This study investigated the localization and the mechanisms of ammonia excretion in mytilid mussels. A Rh protein was found to be abundantly expressed in the apical cell membrane of the plicate organ which was previously described as a solely respiratory organ. The Rh protein was also expressed in the gill, although at significantly lower concentrations, but was not detectable in mussel kidney. Furthermore, NH3/NH4+ was not enriched in the urine suggesting that kidneys are not involved in active NH3/NH4+ excretion. Exposure to elevated seawater pH of 8.5 transiently reduced NH3/NH4+ excretion rates, but they returned to control values following 24h acclimation. This mussels had increased abundance of V-type H+-ATPase in the apical membranes of plicate organ cells: however, NH3/NH4+ excretion rates were not affected by the V-type H+-ATPase specific inhibitor concanamycin A (100 nM). On the other hand, inhibition of ciliary beating with dopamine and increased seawater viscosity significantly reduced NH3 excretion rates under control pH (8.0). These results suggest that NH3/NH4+ excretion in mytilid mussels takes place by passive NH3 diffusion across respiratory epithelia via the Rh protein, facilitated by the water current produced for filter feeding which prevents accumulation of NH3 in the boundary layer. This mechanism would be energy efficient for sessile organisms, since they already generate water currents for filter feeding.

Beschreibung: 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.

Beschreibung: Laboratory experiments were conducted in the climate chambers at GEOMAR Helmholtz Centre for Ocean Research Kiel in the time between March and November 2018. Experiments were designed to study the effect of long-term (1 month) exposure to low salinity in osmoconforming invertebrates. The study organisms (Asterias rubens, Mytilus edulis, Littorina littorea, Diadumene lineata, Strongylocentrotus droebachiensis and Psammechinus milliaris) were collected in Kiel Fjord, Eckernförder Bight or the Kattegat from spring to autumn 2018. Organisms were acclimated to climate chamber conditions for 1 week (under habitat salinity, 14˚C, constant aeration) and then subjected to salinity acclimation for 1-2 weeks until the final salinity treatment level was reached. Then different salinity treatments were maintained for 4 weeks. Water physiochemistry (temperature, salinity, pH, nitrite, nitrate, phosphate) was recorded frequently. After the experiment, samples were taken from tissues to measure total osmolality (mosmol/kg) with an osmomat, and inorganic ions (mmol/kg or µmol/g wet mass). Anions were measured with a novel protocol via ion chromatography, cations were measured via flame photometry. Organic osmolytes were measured via 1H-NMR.

Beschreibung: Low-salinity stress can severely affect the fitness of marine organisms. As desalination has been predicted for many coastal areas with ongoing climate change, it is crucial to gain more insight in mechanisms that constrain salinity acclimation ability. Low-salinity induced depletion of the organic osmolyte pool has been suggested to set a critical boundary in osmoconforming marine invertebrates. Whether inorganic ions also play a persistent role during low-salinity acclimation processes is currently inconclusive. We investigated the salinity tolerance of six marine invertebrate species following a four-week acclimation period around their low-salinity tolerance threshold. The species investigated were Asterias rubens, Mytilus edulis, Littorina littorea, Diadumene lineata, Strongylocentrotus droebachiensis and Psammechinus milliaris. To obtain complete osmolyte budgets of seawater, body fluids and tissues we quantified total osmolality (via osmometer), organic osmolytes (methylamine and free amino acids) via 1H-NMR spectroscopy and inorganic osmolytes (anions and cations) via flame photometry and a novel protocol using ion-chromatography. We further determined the fitness proxies survival, growth and tissue water content. Our data show the importance of the organic and inorganic osmolyte pool during low-salinity acclimation. It also shows the importance of specific compounds in some species. This data can be used in future osmolyte and salinity tolerance research. This type of data is essential to establish reliable physiological limits of species in order to estimate consequences of future salinity changes with ongoing climate change. It can be used to assess the salinity tolerance capacity and to obtain a better understanding of the basic mechanisms that are utilized in a wide range of species. The established cellular inorganic and organic osmolyte profiles can build a foundation for applied cellular physiological research, for example for designing suitable buffers for in vitro assays as these buffers need to incorporate complex organic and inorganic osmolyte changes. Knowledge about cellular and whole-organism biochemistry and physiology is absolutely crucial for characterizing the functions of genes that are under selection by climate change stressors. A quantitative knowledge of cellular osmolyte systems is key to understand the evolution of euryhalinity and to characterize targets of selection during rapid adaptation to ongoing desalination.