Description: Corals are globally important calcifiers that exhibit complex responses to anthropogenic warming and acidification. Although coral calcification is supported by high seawater pH, photosynthesis by the algal symbionts of zooxanthellate corals can be promoted by elevated pCO2. To investigate the mechanisms underlying corals' complex responses to global change, three species of tropical zooxanthellate corals (Stylophora pistillata, Pocillopora damicornis, and Seriatopora hystrix) and one species of asymbiotic cold-water coral (Desmophyllum pertusum, syn. Lophelia pertusa) were cultured under a range of ocean acidification and warming scenarios. Under control temperatures, all tropical species exhibited increased calcification rates in response to increasing pCO2. However, the tropical species' response to increasing pCO2 flattened when they lost symbionts (i.e., bleached) under the high-temperature treatments—suggesting that the loss of symbionts neutralized the benefit of increased pCO2 on calcification rate. Notably, the cold-water species that lacks symbionts exhibited a negative calcification response to increasing pCO2, although this negative response was partially ameliorated under elevated temperature. All four species elevated their calcifying fluid pH relative to seawater pH under all pCO2 treatments, and the magnitude of this offset (Δ[H+]) increased with increasing pCO2. Furthermore, calcifying fluid pH decreased along with symbiont abundance under thermal stress for the one species in which calcifying fluid pH was measured under both temperature treatments. This observation suggests a mechanistic link between photosymbiont loss ('bleaching') and impairment of zooxanthellate corals' ability to elevate calcifying fluid pH in support of calcification under heat stress. This study supports the assertion that thermally induced loss of photosymbionts impairs tropical zooxanthellate corals' ability to cope with CO2-induced ocean acidification.

Description: Physiological sensitivity of cold-water corals to ocean change is far less understood than of tropical corals and very little is known about the impacts of ocean acidification and warming on degradative processes of dead coral framework. In a 13-month laboratory experiment, we examined the interactive effects of gradually increasing temperature and pCO2 levels on survival, growth, and respiration of two prominent color morphotypes (colormorphs) of the framework-forming cold-water coral Lophelia pertusa, as well as bioerosion and dissolution of dead framework. Calcification rates tended to increase with warming, showing temperature optima at ~ 14°C (white colormorph) and 10–12°C (orange colormorph) and decreased with increasing pCO2. Net dissolution occurred at aragonite undersaturation (ΩAr 〈 1) at ~ 1000 μatm pCO2. Under combined warming and acidification, the negative effects of acidification on growth were initially mitigated, but at ~ 1600 μatm dissolution prevailed. Respiration rates increased with warming, more strongly in orange corals, while acidification slightly suppressed respiration. Calcification and respiration rates as well as polyp mortality were consistently higher in orange corals. Mortality increased considerably at 14–15°C in both colormorphs. Bioerosion/dissolution of dead framework was not affected by warming alone but was significantly enhanced by acidification. While live corals may cope with intermediate levels of elevated pCO2 and temperature, long-term impacts beyond levels projected for the end of this century will likely lead to skeletal dissolution and increased mortality. Our findings further suggest that acidification causes accelerated degradation of dead framework even at aragonite saturated conditions, which will eventually compromise the structural integrity of cold-water coral reefs.

Description: Cold-water corals are important bioengineers that provide structural habitat for a diverse species community. About 70 % of the presently known scleractinian cold-water corals are expected to be exposed to corrosive waters by the end of this century due to ocean acidification. At the same time, the corals will experience a steady warming of their environment. Studies on the sensitivity of cold-water corals to climate change mainly concentrated on single stressors in short-term incubation approaches, thus not accounting for possible long-term acclimatisation and the interactive effects of multiple stressors. Besides, preceding studies did not test for possible compensatory effects of a change in food availability. In this study a multifactorial long-term experiment (6 months) was conducted with end-of-the-century scenarios of elevated pCO2 and temperature levels in order to examine the acclimatisation potential of the cosmopolitan cold-water coral Lophelia pertusa to future climate change related threats. For the first time multiple ocean change impacts including the role of the nutritional status were tested on L. pertusa with regard to growth, 'fitness', and survival. Our results show that while L. pertusa is capable of calcifying under elevated CO2 and temperature, its condition (fitness) is more strongly influenced by food availability rather than changes in seawater chemistry. Whereas growth rates increased at elevated temperature (+ 4°C), they decreased under elevated CO2 concentrations (800 µatm). No difference in net growth was detected when corals were exposed to the combination of increased CO2 and temperature compared to ambient conditions. A 10-fold higher food supply stimulated growth under elevated temperature, which was not observed in the combined treatment. This indicates that increased food supply does not compensate for adverse effects of ocean acidification and underlines the importance of considering the nutritional status in studies investigating organism responses under environmental changes.

Description: We have measured Mg/Ca, Sr/Ca and Na/Ca in carbonate shells of the deepwater bivalve Acesta excavata. The samples were collected in the Sula reef and the Leksa reef on the Norwegian margin in summer 2014. Measurements were conducted using LA-ICP-MS.Laser ablation was performed using a Resolution M50 193 nm ArF Excimer Laser system (Resonetics), with a 72 μm beam diameter, a pulse rate of 10 Hz and 10 μm/s scan speed. Total sweep time was 0.65 s. Prior to the measurement a fast precleaning pass was conducted at 0.2 mm/s, 10Hz, and 104 μm laser spot size. Elemental ratio analysis was performed with a Thermo-Scientific ELEMENT XR sector field ICP-MS. In total, eight specimens were measured. In three specimens we measuerd perpendicular to the shell to investigate all shell layers. Additionally, we measured all eight samples in the fibrous and microgranular shell section (calcite). The measurements were taken from the ontogenetic oldest part of the bivalve (ventral side), spanning a length of 20 mm.

Description: In a 13-months laboratory experiment conducted in 2014/2015, the interactive effects of gradually increasing temperature and pCO2 levels on survival, growth and respiration of two prominent colour morphotypes (white and orange) of the framework-forming cold-water coral Lophelia pertusa (also known as Desmophyllum pertusum), as well as bioerosion and dissolution of dead coral framework were assessed. In six-week intervals, three treatments (T1: acidification, T2: warming, T3: combined acidification and warming) were gradually increased in their respective manipulated parameters by 1°C and/or 200 µatm pCO2 after an initial two intervals under ambient (near in-situ) conditions. Each treatment consisted of 7 replicates that were manipulated over the course of the experiment and 3 control replicates that remained at ambient conditions throughout the entire duration of the experiment. Each replicate tank consisted of one live coral fragment of the white morphotype, one fragment of the orange morphotype and one dead framework fragment (naturally bioeroded framework material). Dead framework was examined with regard to attached bioeroders and calcifying organisms, the latter being removed prior to the experiment. All coral samples were collected from an inshore Norwegian cold-water coral habitat in the outer Trondheim-Fjord near Nord-Leksa (63°36.4'N, 09°22.7'E) between 150 to 230 m water depth using the manned submersible JAGO (GEOMAR, 2017; doi:10.17815/jlsrf-3-157) during RV POSEIDON (GEOMAR, 2015; doi:10.17815/jlsrf-1-62) cruise POS455 in June/July 2013. In situ conditions at the time of sampling near the corals were 7.7°C in temperature, 35.2 in salinity and ~6 mL/L oxygen concentration. Prior to the experiment, corals were kept in a closed recirculating system of 1,700 L in a climate-controlled laboratory facility at GEOMAR in Kiel at near in situ conditions of temperature and salinity (7.8 145 ± 0.2 °C and 35.8 ± 0.6) for half a year. Calcification/dissolution rates of live corals and bioerosion/dissolution rates of dead coral framework were determined using the buoyant weighing technique (Davies, 1989; doi:10.1007/BF00428135) with a high precision analytical balance (Sartorius CPA225D, readability = 0.1 mg) placed above every individual aquarium for each measurement. Respiration rates were determined via oxygen consumption measurements using an optode-based oxygen analyser (Oxy-10 mini, PreSens GmbH). Mortality was examined during every six-week interval by visual inspection of all live fragments. Dead polyp counts were calculated as percentage of total polyps counts of every individual fragment. Carbonate system parameters were calculated from the two measured parameters total alkalinity (TA) and dissolved inorganic carbon (DIC). TA and DIC samples were taken at the end of every 6-week interval and analyzed via potentiometric open-cell titration (862 Compact Titrosampler, Metrohm) in case of TA and by infrared detection of CO2 using an Automated Infra-Red Inorganic Carbon Analyzer (AIRICA with LI-COR 7000, Marianda) in case of DIC. TA and DIC were corrected against Certified Reference Material from A.G. Dickson (Scripps Institution of Oceanography) and density-corrected. The purpose of this study was to examine thresholds and optima of live corals under gradual increases of ocean acidification and warming and to quantify dissolution and bioerosion rates of dead coral framework to ultimately assess the balance between live coral calcification and degradation of dead coral framework under future ocean conditions.

Description: Sample C1W originates from Sula reef, off Norway, where it was taken with the submersible Jago during Poseidon cruise POS455 (position: 64.1110°N, 8.1187°E, 303 m water depth; white colourmorp. The coral colony fragment was scanned by a Toshiba Aquilion 64 computer tomograph (CT) at the hospital Klinikum Bremen-Mitte with an x-ray source voltage of 120 kV and a current of 600 mA. The CT image stack has a resolution of 0.35 mm in x-direction and y-direction and 0.5 mm resolution in z-direction (0.3 mm reconstruction unit). Images were reconstructed using Toshiba's patented helical cone beam reconstruction technique (TCOT) and are provided in DICOM-format. Polyp-cavity (calice) segmentation was perfromed with the ZIB edition of the Amira software (Stalling et al., 2005; http://amira.zib.de) based on the new method describes in Schmitt et al. (submitted).

Description: All parameters assessed at the end of the experiment (dry weight of the corals/dead coral framework fragments, ash-free dry mass (AFDM), total polyp count, bacterial background respiration in experimental tanks (no corals incubations).

Description: Measured parameters (net calcification/dissolution, net dissolution/bioerosion, respiration, mortality, temperature, salinity, total alkalinity (TA), dissolved inorganic carbon (DIC)) throughout the 6-week experiment intervals under gradual alterations of the manipulation parameters (temperature, pCO2).

Description: It is important to understand how marine calcifying organisms may acclimatize to ocean acidification to assess their survival over the coming century. We cultured the cold water coralline algae, Lithothamnion glaciale, under elevated pCO2 (408, 566, 770, and 1024 μatm) for 10 months. The results show that the cell (inter and intra) wall thickness is maintained, but there is a reduction in growth rate (linear extension) at all elevated pCO2. Furthermore a decrease in Mg content at the two highest CO2 treatments was observed. Comparison between our data and that at 3 months from the same long-term experiment shows that the acclimation differs over time since at 3 months, the samples cultured under high pCO2 showed a reduction in the cell (inter and intra) wall thickness but a maintained growth rate. This suggests a reallocation of the energy budget between 3 and 10 months and highlights the high degree plasticity that is present. This might provide a selective advantage in future high CO2 world.

Description: The ability of coral reefs to engineer complex three-dimensional habitats is central to their success and the rich biodiversity they support. In tropical reefs, encrusting coralline algae bind together substrates and dead coral framework to make continuous reef structures, but beyond the photic zone, the cold-water coral Lophelia pertusa also forms large biogenic reefs, facilitated by skeletal fusion. Skeletal fusion in tropical corals can occur in closely related or juvenile individuals as a result of non-aggressive skeletal overgrowth or allogeneic tissue fusion, but contact reactions in many species result in mortality if there is no ‘self-recognition’ on a broad species level. This study reveals areas of ‘flawless’ skeletal fusion in Lophelia pertusa, potentially facilitated by allogeneic tissue fusion, are identified as having small aragonitic crystals or low levels of crystal organisation, and strong molecular bonding. Regardless of the mechanism, the recognition of ‘self’ between adjacent L. pertusa colonies leads to no observable mortality, facilitates ecosystem engineering and reduces aggression-related energetic expenditure in an environment where energy conservation is crucial. The potential for self-recognition at a species level, and subsequent skeletal fusion in framework-forming cold-water corals is an important first step in understanding their significance as ecological engineers in deep-seas worldwide.