Reef-building corals and their aragonite (CaCO3) skeletons support entire reef ecosystems, yet their formation mechanism is poorly understood. Here we used synchrotron spectromicroscopy to observe the nanoscale mineralogy of fresh, forming skeletons from six species spanning all reef-forming coral morphologies: Branching, encrusting, massive, and table. In all species, hydrated and anhydrous amorphous calcium carbonate nanoparticles were precursors for skeletal growth, as previously observed in a single species. The amorphous precursors here were observed in tissue, between tissue and skeleton, and at growth fronts of the skeleton, within a low-density nano- or microporous layer varying in thickness from 7 to 20 µm. Brunauer-Emmett-Teller measurements, however, indicated that the mature skeletons at the microscale were space-filling, comparable to single crystals of geologic aragonite. Nanoparticles alone can never fill space completely, thus ion-by-ion filling must be invoked to fill interstitial pores. Such ion-by-ion diffusion and attachment may occur from the supersaturated calcifying fluid known to exist in corals, or from a dense liquid precursor, observed in synthetic systems but never in biogenic ones. Concomitant particle attachment and ion-by-ion filling was previously observed in synthetic calcite rhombohedra, but never in aragonite pseudohexagonal prisms, synthetic or biogenic, as observed here. Models for biomineral growth, isotope incorporation, and coral skeletons’ resilience to ocean warming and acidification must take into account the dual formation mechanism, including particle attachment and ion-by-ion space filling.
Continue reading ‘From particle attachment to space-filling coral skeletons’Posts Tagged 'methods'
From particle attachment to space-filling coral skeletons
Published 16 November 2020 Science ClosedTags: calcification, corals, methods
Development of an autonomous dissolved inorganic carbon sensor for oceanic measurements
Published 11 November 2020 Science ClosedTags: chemistry, field, methods, North Atlantic
Since the industrial revolution the CO2 concentrations in the atmosphere have increased from 280 ppm to over 400 ppm, and each year the oceans take up approximately 25% of the annually emitted anthropogenic CO2. This increase in CO2 in the oceans has had a measure able impact on the marine carbonate system, and the resultant increase in the acidity of the ocean is a potential stressor for a range of ecosystems. In order to fully quantify the marine carbonate system there are four variables that can be measured, these are dissolved inorganic carbon (DIC), pH, total alkalinity and partial pressure of CO2. By measuring two of the four variables the others can be determined. Of these variables DIC is the only one without either an underway or in situ sensor, despite being one half of the preferred pairs for observing the carbonate system. To address this technological gap and increase the measurement coverage there is a clear need for an autonomous sensor capable of making quality measurements while having a robust, small physical size, and low power requirements. Presented here are the results of developmental work that has led to a full ocean depth rated autonomous DIC sensor, based on a microfluidic “Lab On Chip” (LOC) design. The final version of the DIC LOC sensor operates by acidifying < 1 ml of seawater, converting the DIC to CO2, which is diffused across a gas permeable membrane into an acceptor solution. The CO2 reacts with the acceptor resulting in a conductivity drop that is measured using a Capacitively Coupled Contactless Conductivity Detector (C4D). Each measurement takes ~15 minutes and the sensor can be set up to perform calibrations in situ. Laboratory testing demonstrated this system has a precision of < 1 µmol kg-1. The sensor was deployed as part of a large EU project aiming to detect a simulated sub-seabed leak of CO2. Over multiple deployments in the North Sea the sensor collected data used to locate the leak. A number of field tests have established the sensor has a precision of < 10 µmol kg-1. This work has demonstrated that this sensor offers potential to fill the current technological gap and collect data that will enhance understanding of the marine carbonate system.
Continue reading ‘Development of an autonomous dissolved inorganic carbon sensor for oceanic measurements’Polymorphs and morphological changes during dissolution in aging of CaCO₃
Published 11 November 2020 Science ClosedTags: chemistry, laboratory, methods
In this study, an experimental setup was designed to achieve accelerated aging of CaCO₃ crystals in the laboratory to simulate the aging of calcite precipitates and biominerals caused by ocean acidification. CaCO₃ was formed in the calcium aqueous solution through the inflow of CO₂ from the atmosphere, and CaCO₃ aging was conducted in the absence and presence of polyacrylic acid (PAA). When PAA increased, the maximum amount of deposited CaCO₃ reduced, and the time to reach the maximum CaCO₃ deposition was longer. However, there was a late onset of dissolution during aging. In the absence of PAA, typical rhombohedra eroded in the form of a plate or irregular sheet, but in the presence of PAA, some calcite nanofibers broke into nanoparticles. During aging, the calcite polymorph was not changed, but the relative intensity of the (104) plane to other peaks became weaker. This observation implied that the crack in the calcite crystals propagated mainly in the (104) plane during aging. This experimental setup demonstrated that CaCO₃ aging caused by ocean acidification can be simulated in the laboratory.
Continue reading ‘Polymorphs and morphological changes during dissolution in aging of CaCO₃’Experimental techniques to assess coral physiology in situ: current approaches and novel insights
Published 6 November 2020 Science ClosedTags: biological response, calcification, corals, methods, physiology, respiration, review
Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency and severity of massive bleaching events in the tropics are highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic issues such as nutrient loading, increased turbidity, and coastal development. The changes in coral metabolism under local or global stress conditions is studied largely through laboratory manipulation and field observations. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to an entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights to metabolic performance under more complex temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of current experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) and their role in indicating the health status of colonies and communities. The state of the art of in situ techniques for experimental and monitoring purposes is explored. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.
Continue reading ‘Experimental techniques to assess coral physiology in situ: current approaches and novel insights’Ideas and perspectives: when ocean acidification experiments are not the same, reproducibility is not tested
Published 4 November 2020 Science ClosedTags: biological response, fish, methods, performance
Can experimental studies on the impacts of ocean acidification be trusted? That question was raised in early 2020 when a high-profile paper failed to corroborate previously-observed impacts of high CO2 on the behavior of coral reef fish. New information on the methodologies used in the replicated
studies now provides the explanation: the experimental conditions were substantially different. High sensitivity to test conditions is characteristic of ocean acidification research; such response variability shows that effects are complex, interacting with many other factors. Open-minded assessment of all research results, both negative and positive, remains the best way to develop process-based understanding of those responses. Whilst replication studies can provide valuable insights and challenges, they can unfortunately also be counter-productive to scientific advancement if carried out in a spirit of confrontation rather than collaboration.
Spectrophotometric loop flow analyzer for high-precision measurement of seawater pH
Published 4 November 2020 Science ClosedTags: chemistry, field, methods, North Pacific
Highlights
- Spectrophotometric seawater pH analyzer was developed based on loop flow analysis.
- The pH analyzer can be used for underway and in situ measurements
- The precision of in situ measurement system first reached 0.0004.
- The pH analyzer showed good stability and accuracy in various environments.
Abstract
Automated instrument for long-term measurement of seawater pH is important for documenting the changes of the marine carbonate system and the impacts of ocean acidification. An automated pH analyzer based on loop flow analysis (LFA-pH) was developed to achieve precise and accurate measurements of seawater pH. The circulating loop allows complete mixing of an indicator and seawater, constant mixing volume of two solutions, and correcting indicator perturbation for each measurement. During laboratory testing, the LFA-pH precision achieved 0.0004, and the accuracy was 0.0017±0.0038 compared with the certified standard buffer at different temperatures. During the 59 day underway measurement across the mid and high latitudes, more than 2500 pH measurements were carried out. LFA-pH showed good stability with high temperature and salinity changes, and measurement results were consistent with the discrete surface seawater pH measurement data. In situ testing of two LFA-pHs was completed near the Zhongyuan pier in Qingdao. The average pH offset between the two LFA-pHs was 0.0010±0.0032 (n=788), with the accuracies of the two LFA-pHs of 0.0012±0.0033 and 0.0005±0.0035 compared to discrete measurements. For continuous measurement, the average power consumption is 3.6 W at a 10 min measurement frequency. Given its low power consumption, high precision, and accuracy, FLA-pH could be adapted for underway and in situ measurements of ocean acidification observations.
Continue reading ‘Spectrophotometric loop flow analyzer for high-precision measurement of seawater pH’Reaching consensus on assessments of ocean acidification trends
Published 30 October 2020 Meetings , Science ClosedTags: chemistry, methods
Scientists are working to establish a common methodology for evaluating rates of change in—and the various mechanisms that affect—acidification across ocean environments.
Media coverage concerning carbon dioxide (CO2) emissions into Earth’s atmosphere most often focuses on how these emissions affect climate and weather patterns. However, atmospheric CO2 is also the primary driver for ocean acidification, because the products of atmospheric CO2 dissolving into seawater reduce seawater’s pH and its concentration of carbonate ions. Since the beginning of the Industrial Revolution, the acidity of the ocean has increased by over 30%.
Some organisms in the ocean may struggle to adapt to increasingly acidified conditions, and even resilient life-forms may have a harder time finding food. Higher CO2 levels in ocean water also make it difficult for shellfish to build their shells and corals to form their reefs, both of which are made of carbonate compounds.Ocean acidification affects the overall health of marine ecosystems as well as societal concerns about food security.Ocean acidification, which affects the overall health of marine ecosystems as well as societal concerns about food security, has emerged as a major concern for decision-makers on local, regional, and global scales. Indeed, ocean acidification is now a headline climate indicator for the World Meteorological Organization.
Continue reading ‘Reaching consensus on assessments of ocean acidification trends’Autonomous measurement of seawater total alkalinity as an enhancement of ocean carbon observations: from performance characterization to long-term field deployment
Published 30 October 2020 Science ClosedTags: chemistry, field, methods, North Atlantic, South Atlantic
Since around the mid of the 18th century, the global atmospheric carbon dioxide (CO2) concentration has significantly increased due to anthropogenic activities. For 2018, around 11.5 GtC yr−1 were emitted by fossil fuel combustion and cement production, and land use changes. A sink for the atmospheric CO2 is the ocean, which has taken up around 2.6 GtC yr−1 in 2018. The relative good understanding of the current global mean oceanic uptake of anthropogenic CO2 is contrasted by a lack of knowledge how the natural carbon cycle will respond regionally to changes introduced by anthropogenic CO2 emissions, like global warming, ocean acidification or ocean deoxygenation. In view of the central role of the oceanic CO2 sink and its vulnerability to these changes, extensive ocean carbon observations are necessary. Over several years, the Ships of Opportunity (SOOP) network provides high-quality CO2 partial pressure (p(CO2)) data of the surface ocean, and, therefore, forms the backbone of the global observation system for the oceanic CO2 sink. However, to get full insight into the marine CO2 system, at least two of the four measurable carbonate variables are required, which are p(CO2), total alkalinity (AT), dissolved inorganic carbon (CT) and pH. The so far common workaround is the prediction of AT by using established temperature-salinity based parameterizations. However, compared with direct measurements, this procedure leads to higher uncertainties and spatiotemporal biases. Therefore, autonomous SOOP-based AT measurements are of great interest and, in the end, should enhance ocean carbon observations. In order to achieve this enhancement, this thesis goals to provide an example of a successful implementation of a novel autonomous analyzer for seawater AT, the CONTROS HydroFIA TA (-4H-JENA engineering GmbH, Germany), on a Carbon-SOOP station operating in the subpolar North Atlantic (together with fundamental guidelines and recommendations leading to high-quality AT data).
Continue reading ‘Autonomous measurement of seawater total alkalinity as an enhancement of ocean carbon observations: from performance characterization to long-term field deployment’A review of mesocosm experiments on heavy metals in marine environment and related issues of emerging concerns
Published 27 October 2020 Science ClosedTags: mesocosms, methods, review
Mesocosms are real-world environmental science tools for bridging the gap between laboratory-scale experiments and actual habitat studies on ecosystem complexities. These experiments are increasingly being applied in understanding the complex impacts of heavy metals, ocean acidification, global warming, and oil spills. The insights of the present review indicate how metals and metal-bound activities impact on various aspects of ecological complexities like prey predator cues, growth, embryonic development, and reproduction. Plankton and benthos are used more often over fish and microbes owing to their smaller size, faster reproduction, amenability, and repeatability during mesocosm experiments. The results of ocean acidification reveal calcification of plankton, corals, alteration of pelagic structures, and plankton blooms. The subtle effect of oil spills is amplified on sediment microorganisms, primary producers, and crustaceans. An overview of the mesocosm designs over the years indicates that gradual changes have evolved in the type, size, design, composition, parameters, methodology employed, and the outputs obtained. Most of the pelagic and benthic mesocosm designs involve consideration of interactions within the water columns, between water and sediments, trophic levels, and nutrient rivalry. Mesocosm structures are built considering physical processes (tidal currents, turbulence, inner cycling of nutrients, thermal stratification, and mixing), biological complexities (population, community, and ecosystem) using appropriate filling containers, and sampling facilities that employ inert materials. The principle of design is easy transportation, mooring, deployment, and free floating structures besides addressing the unique ecosystem-based science problems. The evolution of the mesocosm tools helps in understanding further advancement of techniques and their applications in marine ecosystems.
Continue reading ‘A review of mesocosm experiments on heavy metals in marine environment and related issues of emerging concerns’Extracellular multi-unit recording from the olfactory nerve of teleosts
Published 27 October 2020 Science ClosedTags: biological response, fish, methods, physiology
Recent studies have shown that ocean acidification affects olfactory-driven behavior in fish. This may be due in part to a reduction in olfactory sensitivity in high PCO2/low pH water. To assess the effects of ocean acidification, or olfactory sensitivity in marine fish in general, we propose that extracellular multi-unit recording from the olfactory nerve is the method of choice. Although invasive, it is sensitive, robust, reproducible and independent of external salinity (unlike the electro-olfactogram [EOG], for example). Furthermore, it records a primary sensory input into the CNS, prior to any central processing. We show that this method can show a reduction in olfactory sensitivity that is both temporary and odorant-dependent, using a range of amino acids to construct concentration-response curves and calculate the thresholds of detection.
Continue reading ‘Extracellular multi-unit recording from the olfactory nerve of teleosts’Ghost factors of laboratory carbonate chemistry are haunting our experiments
Published 26 October 2020 Science ClosedTags: chemistry, methods
For many historical and contemporary experimental studies in marine biology, seawater carbonate chemistry remains a ghost factor, an uncontrolled, unmeasured, and often dynamic variable affecting experimental organisms or the treatments to which investigators subject them. We highlight how environmental variability, such as seasonal upwelling and biological respiration, drive variation in seawater carbonate chemistry that can influence laboratory experiments in unintended ways and introduce a signal consistent with ocean acidification. As the impacts of carbonate chemistry on biochemical pathways that underlie growth, development, reproduction, and behavior become better understood, the hidden effects of this previously overlooked variable need to be acknowledged. Here we bring this emerging challenge to the attention of the wider community of experimental biologists who rely on access to organisms and water from marine and estuarine laboratories and who may benefit from explicit considerations of a growing literature on the pervasive effects of aquatic carbonate chemistry changes.
Continue reading ‘Ghost factors of laboratory carbonate chemistry are haunting our experiments’Reply to: Methods matter in repeating ocean acidification studies
Published 22 October 2020 Science ClosedTags: biological response, fish, methods, performance
Replying to P. L. Munday et al. Nature https://doi.org/10.1038/s41586-020-2803-x (2020)
Pioneering papers by Munday and colleagues1,2 have reported profound effects of end-of-century ocean acidification—simulated by experimentally elevated CO2 levels in seawater—on the behaviour of coral reef fishes, such as extreme attraction of prey species to the chemical cues of their predators. Later studies by the same group reported that a range of other behaviours of coral reef fishes, including swimming activity, behavioural lateralization, homing and different predator avoidance behaviours, were also impaired by ocean acidification3 and that predator-escape behaviours in a coral reef mollusc were also impaired through the same physiological mechanism reported for fishes (that is, through effects on ‘GABAA-like receptors’), which led to the idea that “elevated-CO2 could cause behavioural impairment in a broad suite of marine animals”4. In 2014, we initiated experiments to further explore the physiological mechanism(s) that impaired coral reef fish behaviour in elevated levels of CO2; however, we immediately ran into a problem: despite several attempts, and many improvements to the standard methodology used in this field, we were unable to observe an effect of ocean acidification on fish behaviour. Our initial goal changed from what was meant to be a series of original experiments into a three-year effort to transparently examine behavioural effects of ocean acidification in coral reef fishes5; the findings of our study are the basis for the accompanying Comment by Munday et al.6.
Continue reading ‘Reply to: Methods matter in repeating ocean acidification studies’
Methods matter in repeating ocean acidification studies
Published 22 October 2020 Science ClosedTags: biological response, fish, methods, performance
Arising from T. D. Clark et al. Nature https://doi.org/10.1038/s41586-019-1903-y (2020)
In their study, Clark et al.1 suggest that previous studies on the effects of elevated levels of CO2 on the behaviour of coral reef fishes are not repeatable and that ocean acidification does not impair the behaviour of coral reef fishes, even though six significant behavioural effects were detected in their study, each of which was dismissed for a different reason. They then compare the means and variances of six previous ocean acidification studies in fish with a data distribution that is derived from a multi-species compilation of their own data to conclude that the results of previous studies are statistically improbable. However, Clark et al.1 did not closely repeat previous studies, as they did not replicate key species, used different life stages and ecological histories and changed methods in important ways that reduce the likelihood of detecting the effects of ocean acidification.
Continue reading ‘Methods matter in repeating ocean acidification studies’
Ocean acidification impacts on zooplankton
Published 22 October 2020 Science ClosedTags: biological response, methods, review, vents, zooplankton
Rising atmospheric CO2 alters the ocean biochemistry in the process known as ocean acidification (OA). It influences biodiversity at different levels, including zooplankton, which is a key component of aquatic communities and plays a pivotal role in the structure and functioning of marine planktonic food webs as a major link between pelagic primary producers and planktivorous. The effect of OA on the fitness of individual zooplanktonic species has been reported by many studies mostly developed under laboratory conditions. In this context, this chapter reviews the OA effects on zooplankton and describes the potential of natural shallow-water CO2 vents as in situ laboratories. The impact on zooplankton assemblages is shown from a study in the North Atlantic (Azores islands) and the suitability of this area for future studies on marine organisms and ecosystems. Sites with naturally elevated CO2 conditions are described, including which variables and limitations must be considered. Results shown are highly relevant to improve our predictions of the responses of zooplankton to climate change stressors including OA. Future studies including long-term multigenerational exposure to multiple stressors (e.g. increased pCO2 and food shortage) are a priority to understand the adaptation capacity of common species and how the zooplankton communities will shift.
Continue reading ‘Ocean acidification impacts on zooplankton’
Technical note: interpreting pH changes
Published 13 October 2020 Science ClosedTags: chemistry, methods
The number and quality of ocean pH measurements has increased substantially over the past few decades such that trends, variability, and spatial patterns of change are now being evaluated. However, comparing pH changes across domains with different initial pH values can be misleading because a pH change reflects a relative change in the hydrogen ion concentration ([H+]–expressed in mol kg−1) rather than an absolute change in [H+]. We recommend that [H+] be used in addition to pH when describing such changes and provide three examples illustrating why.
Continue reading ‘Technical note: interpreting pH changes’Underway measurement of dissolved inorganic carbon (DIC) in estuarine waters
Published 7 October 2020 Science ClosedTags: chemistry, methods
Dissolved inorganic carbon (DIC) is an important parameter of the marine carbonate system. Underway analyses of DIC are required to describe spatial and temporal changes of DIC in marine systems. In this study, we developed a microvolume flow detection method for the underway determination of DIC in marine waters, using gas-diffusion flow analysis in conjunction with electrical conductivity (EC) measurement. Only an acid carrier reagent (0.2 mol.L−1) and an ultrapure water acceptor are required for the DIC monitoring system. In this system, a sampling loop (100 µL) is used to quantify the injection sample volume, allowing micro-sample volume detection. The water sample reacts with the acid reagent to convert carbonate and bicarbonate species into CO2. The water sample is then carried into a gas-diffusion assembly, where the CO2 diffuses from the sampling stream into the acceptor stream. CO2 in the acceptor is detected subsequently by an electrical conductivity. The limit of DIC detection using ultrapure water is 0.16 mM. A good repeatability is obtained, with a relative standard deviation (RSD) of 0.56% (1 mM, n = 21). The time interval for detecting one sample is 5 min. During the observation period, measurements can be switched between standard solutions and water samples automatically. Accuracy and precision of the instrument is sufficient for the underway observation of marine DIC in estuarine waters.
Continue reading ‘Underway measurement of dissolved inorganic carbon (DIC) in estuarine waters’
Development of an automated transportable continuous system to measure the total alkalinity of seawater
Published 25 September 2020 Science ClosedTags: chemistry, methods
Highlights
- A novel transportable analysis system for continuous total alkalinity was developed.
- It requires small sample volume (<10 mL) and a short time (<5 min).
- The relative uncertainty of our system is less than 0.1%.
- Our system is expected to facilitate in-situ total alkalinity measurement.
Abstract
Anthropogenic CO2 emissions are contributing to global warming and ocean acidification. Rapid and accurate measurements of seawater carbonate chemistry are critical to understand current changes in the ocean and to predict future effects of such changes on marine organisms and ecosystems. Total alkalinity (AT) measurements can be used to directly determine the calcification rate, but they are time-consuming and require large sample volumes. Herein, we describe an automated and transportable flow-through system that can conduct continuous AT measurement using an ion sensitive field effect transistor (ISFET) – Ag/AgCl sensor and three different reference materials. The response time, stability, and uncertainty of our system were evaluated by comparing AT values of calibrated reference materials to those calculated by our system. Our system requires only small amounts of seawater (<10 mL) and a short time per sample (<5 min) to produce results with a relative uncertainty of less than 0.1% (approx. 2.2 μmol kg−1). This system is expected to facilitate easy and rapid in-situ measurement of AT. Continuous AT measurements would enable us to determine short-term calcification responses to changes in light or temperature and improve our understanding of the metabolic mechanisms of creatures such as corals.
A low‐cost modular control system for multistressor experiments
Published 23 September 2020 Science ClosedTags: chemistry, laboratory, methods
Marine organisms and ecosystems face multiple, temporally variable stressors in a rapidly changing world. Realistic experiments that incorporate these aspects of physiological stress are important for advancing our ability to understand, predict, and manage their ecological impacts. However, the experimental systems needed to conduct such experiments can be costly. Here, we describe a low‐cost, modular control system that can be used with seawater sensors and actuators to dynamically manipulate multiple seawater variables. It enables researchers to run a variety of realistic multiple‐stressor, variable exposure experiments with a range of marine organisms. This tank controller system is based on the open‐source Arduino prototyping platform and features a custom‐made circuit board with a 16‐bit analog‐to‐digital converter, a real‐time clock, a MicroSD memory card reader, a high‐voltage transistor array, and solderless screw terminal connectors for easy connection of sensors, actuators, and power supplies. The assembly and use of this controller system does not require extensive electronics engineering or programming experience, and each module can be assembled for under 80 USD in parts. To demonstrate the system’s capabilities, we present seawater manipulations from experiments involving (1) simultaneous manipulations of dissolved oxygen and pH; (2) fluctuating dissolved oxygen levels; and (3) a controlled stepwise decrease in dissolved oxygen at different temperatures. The low cost and high customizability of this Arduino‐based control system can contribute to expanding capacities for running global change experiments for researchers and students worldwide.
Continue reading ‘A low‐cost modular control system for multistressor experiments’
Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community
Published 22 September 2020 Science ClosedTags: adaptation, algae, biological response, BRcommunity, community composition, echinoderms, methods, mollusks, multiple factors, otherprocess, performance, temperature
Ocean acidification and warming are likely to affect the structure and functioning of marine benthic communities. This study experimentally examined the effects of ocean acidification and warming on trophic interactions within a maerl bed community by using stable carbon and nitrogen isotope analysis. Two three‐month experiments were conducted in winter and summer seasons with four different combinations of pCO2 (ambient and elevated pCO2) and temperature (ambient and +3°C). Experimental assemblages were created in tanks held in the laboratory and were composed of calcareous (Lithothamnion corallioides) and fleshy algae (Rhodymenia ardissonei, Solieria chordalis, and Ulva sp.), gastropods (Gibbula magus and Jujubinus exasperatus), and sea urchins (Psammechinus miliaris). Our results showed higher seaweed availability for grazers in summer than winter. Therefore, grazers were able to adapt their diet seasonally. Increased pCO2 and temperature did not modify the trophic structure in winter, while shifts in the contribution of seaweed were found in summer. Combined acidification and warming increased the contribution of biofilm in gastropods diet in summer conditions. Psammechinus miliaris mostly consumed L. corallioides under ambient conditions, while the alga S. chordalis became the dominant food source under high pCO2 in summer. Predicted changes in pCO2 and temperature had complex effects on assemblage trophic structure. Direct effects of acidification and warming on seaweed metabolism may modify their abundance and biomass, affecting their availability for grazers. Climate change may also modify seaweeds’ nutritive value and their palatability for grazers. The grazers we investigated were able to change their diet in response to changes in algal assemblages, an advantage given that warming and acidification alter the composition of algal communities.
Incorporation of minor and trace elements into cultured brachiopods: implications for proxy application with new insights from a biomineralisation model
Published 17 September 2020 Science ClosedTags: chemistry, methods, paleo
Brachiopods present a key fossil group for Phanerozoic palaeo-environmental and palaeo-oceanographical reconstructions, owing to their good preservation and abundance in the geological record. Yet to date, hardly any geochemical proxies have been calibrated in cultured brachiopods and only little is known on the mechanisms that control the incorporation of various key elements into brachiopod calcite. To evaluate the feasibility and robustness of multiple Element/Ca ratios as proxies in brachiopods, specifically Li/Ca, B/Ca, Na/Ca, Mg/Ca, Sr/Ca, Ba/Ca, as well as Li/Mg, we cultured Magellania venosa, Terebratella dorsata and Pajaudina atlantica under controlled experimental settings over a period of more than two years with closely monitored ambient conditions, carbonate system parameters and elemental composition of the culture medium. The experimental setup comprised of two control aquariums (pH0 = 8.0 and 8.15, T = 10 °C) and treatments where pCO2 − pH (pH1 = 7.6 and pH2 = 7.35), temperature (T = 16 °C) and chemical composition of the culture medium were manipulated. Our results indicate that the incorporation of Li and Mg is strongly influenced by temperature, growth effects as well as carbonate chemistry, complicating the use of Li/Ca, Mg/Ca and Li/Mg ratios as straightforward reliable proxies. Boron partitioning varied greatly between the treatments, however without a clear link to carbonate system parameters or other environmental factors. The partitioning of both Ba and Na varied between individuals, but was not systematically affected by changes in the ambient conditions. We highlight Sr as a potential proxy for DIC, based on a positive trend between Sr partitioning and carbonate chemistry in the culture medium. To explain the observed dependency and provide a quantitative framework for exploring elemental variations, we devise the first biomineralisation model for brachiopods, which results in a close agreement between modelled and measured Sr distribution coefficients. We propose that in order to sustain shell growth under increased DIC, a decreased influx of Ca2+ to the calcifying fluid is necessary, driving the preferential substitution of Sr2+ for Ca2+ in the crystal lattice. Finally, we conducted micro-computed tomography analyses of the shells grown in the different experimental treatments. We present pore space – punctae – content quantification that indicates that shells built under increased environmental stress, and in particular elevated temperature, contain relatively more pore space than calcite, suggesting this parameter as a potential novel proxy for physiological stress and even environmental conditions.
