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  • 1
    Publication Date: 2019-02-01
    Description: The structural framework provided by corals is crucial for reef ecosystem function and services, but high seawater temperatures can be detrimental to the calcification capacity of reef-building organisms. The Red Sea is very warm, but total alkalinity (TA) is naturally high and beneficial for reef accretion. To date, we know little about how such detrimental and beneficial abiotic factors affect each other and the balance between calcification and erosion on Red Sea coral reefs, i.e., overall reef growth, in this unique ocean basin. To provide estimates of present-day reef growth dynamics in the central Red Sea, we measured two metrics of reef growth, i.e., in situ net-accretion/-erosion rates (Gnet) determined by deployment of limestone blocks and ecosystem-scale carbonate budgets (Gbudget), along a cross-shelf gradient (25km, encompassing nearshore, midshore, and offshore reefs). Along this gradient, we assessed multiple abiotic (i.e., temperature, salinity, diurnal pH fluctuation, inorganic nutrients, and TA) and biotic (i.e., calcifier and epilithic bioeroder communities) variables. Both reef growth metrics revealed similar patterns from nearshore to offshore: net-erosive, neutral, and net-accretion states. The average cross-shelf Gbudget was 0.66kg CaCO3m−2yr−1, with the highest budget of 2.44kg CaCO3m−2yr−1 measured in the offshore reef. These data are comparable to the contemporary Gbudgets from the western Atlantic and Indian oceans, but lie well below "optimal reef production" (5–10kg CaCO3m−2yr−1) and below maxima recently recorded in remote high coral cover reef sites. However, the erosive forces observed in the Red Sea nearshore reef contributed less than observed elsewhere. A higher TA accompanied reef growth across the shelf gradient, whereas stronger diurnal pH fluctuations were associated with negative carbonate budgets. Noteworthy for this oligotrophic region was the positive effect of phosphate, which is a central micronutrient for reef building corals. While parrotfish contributed substantially to bioerosion, our dataset also highlights coralline algae as important local reef builders. Altogether, our study establishes a baseline for reef growth in the central Red Sea that should be useful in assessing trajectories of reef growth capacity under current and future ocean scenarios.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2014-09-30
    Description: Free-ocean CO2 enrichment (FOCE) systems are designed to assess the impact of ocean acidification on biological communities in situ for extended periods of time (weeks to months). They overcome some of the drawbacks of laboratory experiments and field observations by enabling (1) precise control of CO2 enrichment by monitoring pH as an offset of ambient pH, (2) consideration of indirect effects such as those mediated through interspecific relationships and food webs, and (3) relatively long experiments with intact communities. Bringing perturbation experiments from the laboratory to the field is, however, extremely challenging. The main goal of this paper is to provide guidelines on the general design, engineering, and sensor options required to conduct FOCE experiments. Another goal is to introduce xFOCE, a community-led initiative to promote awareness, provide resources for in situ perturbation experiments, and build a user community. Present and existing FOCE systems are briefly described and examples of data collected presented. Future developments are also addressed as it is anticipated that the next generation of FOCE systems will include, in addition to pH, options for oxygen and/or temperature control. FOCE systems should become an important experimental approach for projecting the future response of marine ecosystems to environmental change.
    Type: Article , PeerReviewed
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  • 3
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    In:  (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 67 pp
    Publication Date: 2013-06-24
    Description: Carbon dioxide plays a central role in the functioning of organisms and ecosystems. For autotrophs, it is the substrate for photosynthesis while for heterotrophs it is a waste product of respiration. For two centuries Human activities, are responsible for an increase from 280 to 380 μatm of the atmospheric pCO2. A further increase up to 1000 μatm is predicted for the 21th century. The ocean surface and the atmosphere are at the equilibrium for CO2. The CO2 dissolving in seawater reduces the pH and increase of corrosiveness of water for shells and skeletons made of calcium carbonates. Thus, this process of ocean acidification is expected to have detrimental effects on calcifying organism. On the contrary, marine autotrophs are supposed to (slightly) benefit from this extra supply of CO2. In this thesis, we aimed at assessing the influence of CO2 on members of the nearshore macrophytes meadows of the Baltic Sea, an ecosystem naturally exposed to elevated water acidity. In a first part, we investigated the natural variations of the carbonate system in a meadow during three weeks of July, August, and September 2011 in a sheltered bay of the Western Baltic. We observed important day night dynamics together with wider scale variations (days to weeks) of magnitude exceeding future climate change predictions. We were able to explain the variations by the action of light and wind speed and direction. Light drives the uptake and release of carbon by photosynthesis and respiration of the meadow and wind influences the upwelling of offshore hypercapnic seawater. In a second part, we investigated the growth response to elevated pCO2 of one of the main primary producer of the meadows, the brown algae Fucus serratus, in laboratory experiments. The algae were incubated under ambient pCO2, actual upwelling pCO2 and future upwelling pCO2. We observed an increase of growth of 20 % at the pCO2 expected for the year 2100 and up to 50 % at pCO2 possibly occurring during future upwelling events (4000 μatm). However, the effect was transient and a limitation of growth by nutrients occurred after about 20 days. In the third part, we tested the effect of at the same three pCO2 on the growth and recruitment of the main members of the sessile associated communities of Fucus serratus: the calcifying and non-calcifying bryozoan Electra pilosa and Alcyonidium hirsutum and the calcifying tubeworm Spirorbis spirorbis. We tested the hypothesis of greater sensitivity of calcifyers to acidification and found a resistance of all the tested organisms to the future ambient pCO2. In contrast, at the highest pCO2 tested (future upwelling), we observed in Spirorbis severe shell corrosion, reduction of growth and collapse of recruitment. The growth rates of the worm settlings were assessed at light and dark under the three experimental pCO2. A 40 % enhancement of growth was observed at light at any pCO2, possibly due to the algal photosynthetic reduction of pCO2 / increase of pH in the boundary layer surrounding the algal thallus. Our study illustrates the possibility of facilitation between species to resist ocean acidification.
    Type: Thesis , NonPeerReviewed
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  • 4
    Publication Date: 2019-08-08
    Description: 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 fluctuations 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.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 5
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    PANGAEA
    In:  Supplement to: Saderne, Vincent (2012): The ecological effect of CO2 on the brown algae Fucus serratus and its epibionts: From the habitat to the organismic scale. PhD Thesis, Christian-Albrechts-University of Kiel, Germany, 0-67, http://eldiss.uni-kiel.de/macau/receive/dissertation_diss_00010109
    Publication Date: 2019-09-26
    Description: The brown algae Fucus serratus is one of the major meadow forming algae of the Western Baltic Sea nearshore ecosystem. At the end of summer, those meadows are exposed to local upwelling suddenly increasing the pCO2 and DIC up to 2500 µatm and 2250 µmol/kg resp., for period of days to weeks. This study investigates the growth response of summer's vegetative Fucus serratus to elevated pCO2 (1350 and 4080 µatm) during a 40 days laboratory incubation. After 10 days, increases of growth rates of 20 % and 47 % of the control were observed in the 1350 and 4080 µatm pCO2 treatments respectively. Beyond 20 days, the growth rates collapsed in all treatments due to nutrients shortage, as demonstrated by high C:N ratios (95:1) and low N tissue content (0.04 % of dry weight). The collapse occurs faster at higher pCO2. On day 30, growth rates were reduced by 40 % and 100 % relative to the control at 1350 and 4080 µatm respectively. These results are consistent with a fertilizing effect of elevated pCO2 on Fucus serratus presumably linked to the transition from active HCO3- to passive CO2(aq) uptake. This positive effect is limited by nutrients resources, low seawater dissolved inorganic N and P and shortage of the nutrients reserves accumulated over the previous autumn and winter.
    Type: Dataset
    Format: text/tab-separated-values, 8188 data points
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  • 6
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    PANGAEA
    In:  Supplement to: Saderne, Vincent; Wahl, Martin (2013): Differential Responses of Calcifying and Non-Calcifying Epibionts of a Brown Macroalga to Present-Day and Future Upwelling pCO2. PLoS ONE, 8(7), e70455, https://doi.org/10.1371/journal.pone.0070455.t001
    Publication Date: 2019-09-26
    Description: Seaweeds are key species of the Baltic Sea benthic ecosystems. They are the substratum of numerous fouling epibionts like bryozoans and tubeworms. Several of these epibionts bear calcified structures and could be impacted by the high pCO2 events of the late summer upwellings in the Baltic nearshores. Those events are expected to increase in strength and duration with global change and ocean acidification. If calcifying epibionts are impacted by transient acidification as driven by upwelling events, their increasing prevalence could cause a shift of the fouling communities toward fleshy species. The aim of the present study was to test the sensitivity of selected seaweed macrofoulers to transient elevation of pCO2 in their natural microenvironment, i.e. the boundary layer covering the thallus surface of brown seaweeds. Fragments of the macroalga Fucus serratus bearing an epibiotic community composed of the calcifiers Spirorbis spirorbis (Annelida) and Electra pilosa (Bryozoa) and the non-calcifier Alcyonidium hirsutum (Bryozoa) were maintained for 30 days under three pCO2 conditions: natural 460±59 µatm, present-day upwelling1193±166 µatm and future upwelling 3150±446 µatm. Only the highest pCO2 caused a significant reduction of growth rates and settlement of S. spirorbis individuals. Additionally, S. spirorbis settled juveniles exhibited enhanced calcification of 40% during daylight hours compared to dark hours, possibly reflecting a day-night alternation of an acidification-modulating effect by algal photosynthesis as opposed to an acidification-enhancing effect of algal respiration. E. pilosa colonies showed significantly increased growth rates at intermediate pCO2 (1193 µatm) but no response to higher pCO2. No effect of acidification on A. hirsutum colonies growth rates was observed. The results suggest a remarkable resistance of the algal macro-epibionts to levels of acidification occurring at present day upwellings in the Baltic. Only extreme future upwelling conditions impacted the tubeworm S. spirorbis, but not the bryozoans.
    Type: Dataset
    Format: text/tab-separated-values, 4408 data points
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  • 7
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    PANGAEA
    In:  Supplement to: Wahl, Martin; Saderne, Vincent; Sawall, Yvonne (2016): How good are we at assessing the impact of ocean acidification in coastal systems? Limitations, omissions and strengths of commonly used experimental approaches with special emphasis on the neglected role of fluctuations. Marine and Freshwater Research, 67(1), 25, https://doi.org/10.1071/MF14154
    Publication Date: 2019-09-26
    Description: These data form the basis of an analysis of a prevalent research bias in the field of ocean acidification, notably the ignoring of natural fluctuations and gradients in the experimental design. The data are extracted from published work and own experiments.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 8
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    PANGAEA
    In:  Supplement to: Rossbach, Susann; Saderne, Vincent; Anton, Andrea; Duarte, Carlos M (2019): Light-dependent calcification in Red Sea giant clam 〈i>Tridacna maxima〈/i>. Biogeosciences, 16(13), 2635-2650, https://doi.org/10.5194/bg-16-2635-2019
    Publication Date: 2019-09-26
    Description: Abundance data of Tridacna maxima giant clams at 6 different depths (0.5, 1.5, 3, 5 , 8 and 11m) at two reefs (Station 1 - 22.303833 N, 39.048278 E) and Station 2 - 20.753764 N, 39.442561 E ) in the Central Red Sea. Primary production in Tridacna maxima giant clams was assessed during the three different incident light incubations (561, 959, and 1061 μmol quanta m-2 s-1). Oxygen (μmol L-1) content in the incubation chambers was automatically logged (miniDOT, Precision Measurement Engineering, Inc., USA) in 15 min intervals over the 3 h incubation period. Net photosynthesis (NPP) was calculated from the variation of oxygen concentration over time and normalized for clam mantle surface area (μmol O2 cm-2 h-1). Dark respiration rates (R), also given in μmol O2 cm-2 h-1, were used to calculate gross primary production (GPP) as: GPP = NPP +R. Net calcification rates of the giant clam Tridacna maxima were determined under 7 different light levels (1061,959, 561, 530, 358, 244, and 197 μmol quanta m-2 s-1) and in the dark. At the start, after 3 h and after 6 h of each incubation, seawater was sampled from each experimental aquaria in gas tight 100mL borosilicate bottles (Schott Duran, Germany) and poisoned with mercury chloride, following Dickson et al. (2011). Each sample was analysed for TA by open-cell titration with an AS-ALK2 titrator (Apollo SciTech,USA) using certified seawater reference material (Andrew Dickson, Scripps Institution of Oceanography). During the incubations at moderate light levels (530, 358, 244,and 197 μmol quanta m-2 s-1), additional samples for dissolved inorganic carbon (DIC) were analysed using an ASC3 infrared DIC analyser (Apollo SciTech, USA). Further components of the carbonate system were calculated with R package Seacarb (Lavigne and Gattuso, 2013) using first and second carbonate system dissociation constants of Millero (2010) as well as the dissociations of HF and HSO-4 (Dickson, 1990; Dickson and Goyet, 1994), respectively. Net calcification (G in μmol CaCO3 h-1) was estimated from changes in total alkalinity (TA) using the alkalinity anomaly technique (Smith and Key, 1975), where delta TA is the variation of TA during the time (t ) of the incubations and the factor 2 accounts for a decrease in TA by two equivalents per CaCO3 precipitated (Zeebe and Wolf-Gladrow, 2001). Calcification rates were expressed relative to either mantle surface area (cm2) or tissue dry mass (g). For mantle surface area, the power relationship between standard length in centimetres (L) and mantle area (cm2) (Jantzen et al., 2008) was used to calculate the mantle surface in cm2. For tissue dry mass (DM in gram) of 5 clams, all clams were dissected and their biomass was determined subsequently to the incubation experiment. Clams were opened by cutting the adductor muscle with a scalpel, and the mantle and other tissues were separated from the shells and dried at 60 Degree Celsius for 24 to 48 h to determine tissue DM to the nearest 0.01 g.
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 9
    Publication Date: 2019-09-23
    Description: Mussel and seagrass beds are characteristic of the shallow nearshores of the western Baltic Sea, forming a mosaic of habitat. The diverse physiological activities of seagrasses and mussels are affected by seawater carbonate chemistry and in return locally modify it. Seagrass photosynthesis decreases seawater CO2 concentration at daytime and increases it at night through respiration. This dynamic creates very favorable chemical condition to calcification at daytime but turn the habitat corrosive to calcium carbonates at night. In contrast, mussel respiration releases CO2, with the potential of locally changing the carbonate chemistry, turning the environment more favorable for photosynthesis by adjacent seagrass. Mussel calcification has the potential for reducing alkalinity (uptake of CO32-) thereby increasing CO2 concentration in seawater and reciprocally once dead, due to the dissolution of the shells. To capture these interactions between habitats, we 1) used a combination of state-of-the-art technologies to create an in-situ high precision carbonate sensor suite and 2) deployed it in August and September 2013 at the interface between a seagrass and a mussel patch submitted to series of down- and upwelling events.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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