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Seawater carbonate chemistry and physiology of Baltic blue mussels (Mytilus edulis)

Increased maintenance costs at cellular, and consequently organism level, are thought to be involved in shaping the sensitivity of marine calcifiers to ocean acidification (OA). Yet, knowledge of the capacity of marine calcifiers to undergo metabolic adaptation is sparse. In Kiel Fjord, blue mussels thrive despite periodically high seawater PCO2, making this population interesting for studying metabolic adaptation under OA. Consequently, we conducted a multi-generation experiment and compared physiological responses of F1 mussels from 'tolerant' and 'sensitive' families exposed to OA for 1 year. Family classifications were based on larval survival; tolerant families settled at all PCO2 levels (700, 1120, 2400 µatm) while sensitive families did not settle at the highest PCO2 (>=99.8% mortality). We found similar filtration rates between family types at the control and intermediate PCO2 level. However, at 2400 µatm, filtration and metabolic scope of gill tissue decreased in tolerant families, indicating functional limitations at the tissue level. Routine metabolic rates (RMR) and summed tissue respiration (gill and outer mantle tissue) of tolerant families were increased at intermediate PCO2, indicating elevated cellular homeostatic costs in various tissues. By contrast, OA did not affect tissue and routine metabolism of sensitive families. However, tolerant mussels were characterised by lower RMR at control PCO2 than sensitive families, which had variable RMR. This might provide the energetic scope to cover increased energetic demands under OA, highlighting the importance of analysing intra-population variability. The mechanisms shaping such difference in RMR and scope, and thus species' adaptation potential, remain to be identified.

Seawater carbonate chemistry and in situ and laboratory measurements of calcification

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.

Physical oceanography during RV HEINCKE cruise HE659

Conductivity-temperature-depth profiles were measured using a Seabird SBE 911plus CTD during RV HEINCKE cruise HE659. The CTD was equipped with duplicate sensors for temperature (SBE3plus), conductivity (SBE4) and oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer and an altimeter (PSA-916 Teledyne (Benthos)) were mounted to the CTD. Temperature, conductivity and oxygen sensors are calibrated by the manufacturer once a year before being mounted in January. They are used throughout the year and no post-cruise or in-situ calibration is applied. All other sensors are calibrated irregularly. Data were connected to the station book of the specific cruise as available in the DSHIP database. Processing of the data including removal of obvious outliers followed the procedures described in CTD Processing Logbook of RV HEINCKE (hdl:10013/epic.47427). The processing report for this dataset is linked below.

The benthic foraminiferal community in a naturally CO2-rich coastal habitat of the southwestern Baltic Sea

It is expected that the calcification of foraminifera will be negatively affected by the ongoing acidification of the oceans. Compared to the open oceans, these organisms are subjected to much more adverse carbonate system conditions in coastal and estuarine environments such as the southwestern Baltic Sea, where benthic foraminifera are abundant. This study documents the seasonal changes of carbonate chemistry and the ensuing response of the foraminiferal community with bi-monthly resolution in Flensburg Fjord. In comparison to the surface pCO2, which is close to equilibrium with the atmosphere, we observed large seasonal fluctuations of pCO2 in the bottom and sediment pore waters. The sediment pore water pCO2 was constantly high during the entire year ranging from 1244 to 3324 µatm. Nevertheless, in contrast to the bottom water, sediment pore water was slightly supersaturated with respect to calcite as a consequence of higher alkalinity (AT) for most of the year. Foraminiferal assemblages were dominated by two calcareous species, Ammonia aomoriensis and Elphidium incertum, and the agglutinated Ammotium cassis. The one-year cycle was characterised by seasonal community shifts. Our results revealed that there is no dynamic response of foraminiferal population density and diversity to elevated sediment pore water pCO2. Surprisingly, the fluctuations of sediment pore water undersaturation (Omega calc) co-vary with the population densities of living Ammonia aomoriensis. Further, we observed that most of the tests of living calcifying foraminifera were intact. Only Ammonia aomorienis showed dissolution and recalcification structures on the tests, especially at undersaturated conditions. Therefore, the benthic community is subjected to high pCO2 and tolerates elevated levels as long as sediment pore water remains supersaturated. Model calculations inferred that increasing atmospheric CO2 concentrations will finally lead to a perennial undersaturation in sediment pore waters. Whereas benthic foraminifera indeed may cope with a high sediment pore water pCO2, the steady undersaturation of sediment pore waters would likely cause a significant higher mortality of the dominating Ammonia aomoriensis. This shift may eventually lead to changes in the benthic foraminiferal communities in Flensburg Fjord, as well as in other regions experiencing naturally undersaturated Omega calc levels.

Impact of ocean acidification on thermal tolerance and acid-base regulation of Mytilus edulis (L.) from the North Sea

Seawater carbonate chemistry and effects of ocean acidification on different life-cycle stages of the kelp Laminaria hyperborea (Phaeophyceae) in a laboratory experiment

Raw data of physical oceanography during RV HEINCKE cruise HE662

Raw physical oceanography data was acquired by a ship-based Seabird SBE911plus CTD-Rosette system onboard RV HEINCKE . The CTD was equipped with duplicate sensors for temperature (SBE3plus) and conductivity (SBE4) as well as one sensor for oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer (FLRTD) and an altimeter (Teledyne Benthos PSA-916) were mounted to the CTD. The data was recorded using pre-cruise calibration coefficients. No correction, post-cruise calibration or quality control was applied. Processed profile data are available via the link below.

Physical oceanography during RV HEINCKE cruise HE672

Conductivity-temperature-depth profiles were measured using a Seabird SBE 911plus CTD during RV HEINCKE cruise HE672. The CTD was equipped with duplicate sensors for temperature (SBE3plus), conductivity (SBE4) and oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer and an altimeter (PSA-916 Teledyne (Benthos)) were mounted to the CTD. Temperature, conductivity and oxygen sensors are calibrated by the manufacturer once a year before being mounted in January. They are used throughout the year and no post-cruise or in-situ calibration is applied. All other sensors are calibrated irregularly. Data were connected to the station book of the specific cruise as available in the DSHIP database. Processing of the data including removal of obvious outliers followed the procedures described in CTD Processing Logbook of RV HEINCKE (hdl:10013/epic.47427). The processing report for this dataset is linked below.

Raw data of physical oceanography during RV HEINCKE cruise HE669

Raw physical oceanography data was acquired by a ship-based Seabird SBE911plus CTD-Rosette system onboard RV HEINCKE. The CTD was equipped with duplicate sensors for temperature (SBE3plus) and conductivity (SBE4) as well as one sensor for oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer (FLRTD) and an altimeter (Teledyne Benthos PSA-916) were mounted to the CTD. The data was recorded using pre-cruise calibration coefficients. No correction, post-cruise calibration or quality control was applied. Processed profile data are available via the link below.

Physical oceanography during RV HEINCKE cruise HE669

Conductivity-temperature-depth profiles were measured using a Seabird SBE 911plus CTD during RV HEINCKE cruise HE669. The CTD was equipped with duplicate sensors for temperature (SBE3plus), conductivity (SBE4) and oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer and an altimeter (PSA-916 Teledyne (Benthos)) were mounted to the CTD. Temperature, conductivity and oxygen sensors are calibrated by the manufacturer once a year before being mounted in January. They are used throughout the year and no post-cruise or in-situ calibration is applied. All other sensors are calibrated irregularly. Data were connected to the station book of the specific cruise as available in the DSHIP database. Processing of the data including removal of obvious outliers followed the procedures described in CTD Processing Logbook of RV HEINCKE (hdl:10013/epic.47427). The processing report for this dataset is linked below.

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