Posts Tagged 'individualmodeling'

Ocean afforestation’s effect on deep-sea biogeochemistry

If climate change is left unchecked it will lead to unprecedented deterioration of human health, economy and ecology. According to the IPCC, in order to avoid severe consequences, global warming will need to be limited to 1.5°C. However, the 1.5°C warming will be exceeded if current trends continue, which is why the need for Carbon Dioxide Removal (CDR) has become increasingly apparent. Ocean afforestation is currently one of the most promising CDR approaches, with the least competition for space, high carbon sequestration potential and high technical feasibility. Ocean afforestation approaches attempt to sequester carbon by sinking seaweed to deep-sea areas. This research looks at the consequences of the seaweed input to deep-seafloor. An early diagenetic model called RADI is used to predict the fate of the carbon and the effect on biogeochemistry. The model was adapted to include new sources of sedimentary organic matter, such as seaweed (Sargassum, Saccharina, Macrocystis) and Sugarcane bagasse, which are currently considered potential candidates for ocean afforestation purposes. Sargassum, an invasive free-floating species, has a large sequestration potential and is readily available. Sinking Sargassum in pulse, large amounts over short times, leads to high carbon retention in the sediment (up to 25% after two years) but leads to hypoxic conditions in the sediment for at least two years after addition. Continuous Sargassum sinking also leads to carbon sequestration but with a much less invasive impact on the seafloor. The carbon from continuous sinking does not remain in the sediment but is remineralized and flows out to the bottom water as inorganic carbon. Saccharina, an edible coastal species, could be used to grow on free floating organic buoy. Having the additional sequestration benefit from the carbon fixed in the organics. Carbon retention is highest for the pulse addition of this seaweed (33% after two years), compared to a continuous approach (30%) in which the seaweed is added over longer timescales in small amounts. Since this pulse input also leads to hypoxic conditions in the sediment, the continuous approach is more favourable for this approach. Macrocystis, the giant kelp known for forming ecosystems, is a fast-growing coastal species. This species requires harvesting and baling for use in carbon sequestration. Carbon retention is much higher for pulse addition (30%). Sugar cane bagasse is an agricultural residue with high carbon content. Sinking this residue to anoxic basins, has been proven to retain more carbon than in oxygenated bottom waters. This can be confirmed with the results which showed a carbon retention of up to 50% after two years. The effect on the benthic biome is also less intense since the low oxygen conditions already necessitate a specialized microbiome. Sugarcane bagasse is furthermore the only addition capable of increasing bottom water pH. Whereas all seaweed approaches had higher dissolved inorganic carbon than alkalinity flow to the bottom water, resulting in net acidification. This research provides a first look into the effects of ocean afforestation on deep sea biogeochemistry, and illustrates the importance of the composition, quantity and input duration of the seaweed used.

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Reduction in size of the calcifying phytoplankton Calcidiscus leptoporus to environmental changes between the Holocene and modern Subantarctic Southern Ocean

The Subantarctic Zone of the Southern Ocean plays a disproportionally large role on the Earth system. Model projections predict rapid environmental change in the coming decades, including ocean acidification, warming, and changes in nutrient supply which pose a serious risk for marine ecosystems. Yet despite the importance of the Subantarctic Zone, annual and inter-annual time series are extremely rare, leading to important uncertainties about the current state of its ecosystems and hindering predictions of future response to climate change. Moreover, as the longest observational time series available are only a few decades long, it remains unknown whether marine pelagic ecosystems have already responded to ongoing environmental change during the industrial era. Here, we take advantage of multiple sampling efforts – monitoring of surface layer water properties together with sediment trap, seafloor surface sediment and sediment core sampling – to reconstruct the modern and pre-industrial state of the keystone calcifying phytoplankton Calcidiscus leptoporus, central to the global marine carbonate cycle. Morphometric measurements reveal that modern C. leptoporus coccoliths are 15% lighter and 25% smaller than those preserved in the underlying Holocene-aged sediments. The cumulative effect of multiple environmental drivers appears responsible for the coccolith size variations since the Last Deglaciation, with warming and ocean acidification most likely playing a predominant role during the industrial era. Notably, extrapolation of our results suggests a future reduction in cell and coccolith size which will have a negative impact on the efficiency of the biological pump in the Southern Ocean through a reduction of carbonate ballasting. Lastly, our results tentatively suggest that C. leptoporus coccolith size could be used as a palaeo-proxy for growth rate. Future culture experiments will be needed to test this hypothesis.

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Sr/Ca in foraminiferal calcite as a proxy for calcifying fluid composition

Foraminifera are unicellular organisms that inhabit the oceans. They play an important role in the global carbon cycle and record valuable paleoclimate information through the uptake of trace elements such as strontium (Sr) into their calcitic (CaCO3) shells. Understanding how foraminifera control their internal fluid composition to make CaCO3 is important for predicting their response to ocean acidification and for reliably interpreting the chemical and isotopic compositions of their shells. Here, we model foraminiferal calcification and strontium partitioning in the benthic foraminifera Cibicides wuellerstorfi and Cibicidoides mundulus based on insights from inorganic calcite experiments. The model reconciles inter-ocean and taxonomic differences in benthic foraminifer Sr/Ca partitioning relationships and enables us to reconstruct the composition of the calcifying fluid. We find that Sr partitioning and mineral growth rates of foraminiferal calcite are not significantly affected by changes in external seawater pH (within 7.8–8.1) and [DIC] (within 2100–2300 µmol/kg) due to a regulated calcite saturation state at the site of shell formation. Such homeostasis of the calcifying fluid could explain why foraminifera have been resilient to changes in ocean carbonate chemistry for more than 500 million years. Nevertheless, our model indicates that past foraminiferal DSr values were lower than its modern value due to overall lower ocean pH and higher seawater temperature during the early and middle Cenozoic.

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Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean

Climate change impacts on fishery resources have been widely reported worldwide. Nevertheless, a knowledge gap remains for the warm-temperate Southwest Atlantic Ocean—a global warming hotspot that sustains important industrial and small-scale fisheries. By combining a trait-based framework and long-term landing records, we assessed species’ sensitivity to climate change and potential changes in the distribution of important fishery resources (n = 28; i.e., bony fishes, chondrichthyans, crustaceans, and mollusks) in Southern Brazil, Uruguay, and the northern shelf of Argentina. Most species showed moderate or high sensitivity, with mollusks (e.g., sedentary bivalves and snails) being the group with the highest sensitivity, followed by chondrichthyans. Bony fishes showed low and moderate sensitivities, while crustacean sensitivities were species-specific. The stock and/or conservation status overall contributed the most to higher sensitivity. Between 1989 and 2019, species with low and moderate sensitivity dominated regional landings, regardless of the jurisdiction analyzed. A considerable fraction of these landings consisted of species scoring high or very high on an indicator for potential to change their current distribution. These results suggest that although the bulk of past landings were from relatively climate-resilient species, future catches and even entire benthic fisheries may be jeopardized because (1) some exploited species showed high or very high sensitivities and (2) the increase in the relative representation of landings in species whose distribution may change. This paper provides novel results and insights relevant for fisheries management from a region where the effects of climate change have been overlooked, and which lacks a coordinated governance system for climate-resilient fisheries.

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Evaluating environmental controls on the exoskeleton density of larval Dungeness crab via micro computed tomography

Dungeness crab (Metacarcinus magister) have significant socioeconomic value, but are threatened by ocean acidification (OA) and other environmental stressors that are driven by climate change. Despite evidence that adult harvests are sensitive to the abundance of larval populations, relatively little is known about how Dungeness megalopae will respond to these stressors. Here we evaluate the ability to use micro-computed tomography (μCT) to detect variations in megalope exoskeleton density and how these measurements reflect environmental variables and calcification mechanisms. We use a combination of field data, culture experiments, and model simulations to suggest resolvable differences in density are best explained by minimum pH at the time zoeae molt into megalopae. We suggest that this occurs because more energy must be expended on active ion pumping to reach a given degree of calcite supersaturation at lower pH. Energy availability may also be reduced due to its diversion to other coping mechanisms. Alternate models based on minimum temperature at the time of the zoea-megalope molt are nearly as strong and complicate the ability to conclusively disentangle pH and temperature influences. Despite this, our results suggest that carryover effects between life stages and short-lived extreme events may be particularly important controls on exoskeleton integrity. μCT-based estimates of exoskeleton density are a promising tool for evaluating the health of Dungeness crab populations that will likely provide more nuanced information than presence-absence observations, but future in situ field sampling and culture experiments are needed to refine and validate our results.

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Dynamics of an aquatic diffusive predator–prey model with double Allee effect and pH-dependent capture rate

To investigate ocean acidification and Allee effects on the dynamics of a marine predator–prey system, an aquatic diffusive predator–prey model with double Allee effect on prey and pH-dependent capture rate is considered. First, we study the stability of constant steady state solutions using linearized theory. Second, the nonexistence of nonconstant positive steady state solutions is shown for appropriate ranges of parameters. Furthermore, we show the existence of a Hopf bifurcation and derive the direction and stability of the bifurcating periodic solutions. Both theoretical analysis and numerical simulation show that changing predator–prey interaction strengths, due to changing environmental conditions, can fundamentally change the system dynamics, even for apparently small changes in interaction strength. As the interaction strength decreases due to decreasing ocean pH, the system dynamics transition from persistent fluctuations in species abundances (periodic solutions), to stable coexistence, to predator extinct (with stable non-zero prey abundance), suggesting the potential for ocean acidification to decrease the abundance and diversity of marine species by weakening predation rates. Moreover, double Allee effect parameters together determine the stability of periodic solutions when the spatially homogeneous bifurcating periodic solutions exist, and the wavelength becomes longer as the Allee effect increases.

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Potential ecosystem regime shift resulting from elevated CO2 and inhibition of macroalgal recruitment by turf algae

Rising carbon dioxide (CO2) concentrations are predicted to cause an undesirable transition from macroalgae-dominant to turf algae-dominant ecosystems due to its effect on community structuring processes. As turf algae are more likely to proliferate due to the CO2 fertilization effect than macroalgae and often inhibit macroalgal recruitment, increased CO2 beyond certain levels may produce novel positive feedback loops that promote turf algae growth and thus can stabilize turf algae-dominant ecosystems. In this study, we built a simple competition model between macroalgae and turf algae in a homogeneous space to investigate the steady-state response of the ecosystem to changes in the partial pressure of CO2 (pCO2). We found that discontinuous regime shifts in response to pCO2 change can occur once turf algae coverage reaches a critical level capable of inhibiting macroalgal recruitment. The effect of localized turf algae density on the success rate of macroalgae recruitment was also investigated using a patch model that simulated a two-dimensional heterogeneous space. This suggested that in addition to the inhibitory effect by turf algae, a self-enhancing effect by macroalgae could also be important in predicting the potential discontinuous regime shifts in response to future pCO2 changes.

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Testing hypotheses on the calcification in scleractinian corals using a spatio-temporal model that shows a high degree of robustness


  • Several hypotheses on coral calcification are tested using a computational model.
  • The model is able to reproduce the experimental data of three separate studies.
  • The model finds that paracellular ion transport into the ECM plays a minor role.
  • Implementing OA in the model increased the calcification rate and ATP consumption.
  • In the model, LEC is the result of increased metabolism and Ca2+-ATPase activity.


Calcification in photosynthetic scleractinian corals is a complicated process that involves many different biological, chemical, and physical sub-processes that happen within and around the coral tissue. Identifying and quantifying the role of separate processes in vivo or in vitro is difficult or not possible. A computational model can facilitate this research by simulating the sub-processes independently. This study presents a spatio-temporal model of the calcification physiology, which is based on processes that are considered essential for calcification: respiration, photosynthesis, Ca2+-ATPase, carbonic anhydrase. The model is used to test different hypotheses considering ion transport across the calicoblastic cells and Light Enhanced Calcification (LEC). It is also used to quantify the effect of ocean acidification (OA) on the Extracellular Calcifying Medium (ECM) and ATP-consumption of Ca2+-ATPase. It was able to reproduce the experimental data of three separate studies and finds that paracellular transport plays a minor role compared to transcellular transport. In the model, LEC results from increased Ca2+-ATPase activity in combination with increased metabolism. Implementing OA increases the concentration of CO2 throughout the entire tissue, thereby increasing the availability of CO3− in the ECM. As a result, the model finds that calcification becomes more energy-demanding and the calcification rate increases.

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Phosphate limitation intensifies negative effects of ocean acidification on globally important nitrogen fixing cyanobacterium

Growth of the prominent nitrogen-fixing cyanobacterium Trichodesmium is often limited by phosphorus availability in the ocean. How nitrogen fixation by phosphorus-limited Trichodesmium may respond to ocean acidification remains poorly understood. Here, we use phosphate-limited chemostat experiments to show that acidification enhanced phosphorus demands and decreased phosphorus-specific nitrogen fixation rates in Trichodesmium. The increased phosphorus requirements were attributed primarily to elevated cellular polyphosphate contents, likely for maintaining cytosolic pH homeostasis in response to acidification. Alongside the accumulation of polyphosphate, decreased NADP(H):NAD(H) ratios and impaired chlorophyll synthesis and energy production were observed under acidified conditions. Consequently, the negative effects of acidification were amplified compared to those demonstrated previously under phosphorus sufficiency. Estimating the potential implications of this finding, using outputs from the Community Earth System Model, predicts that acidification and dissolved inorganic and organic phosphorus stress could synergistically cause an appreciable decrease in global Trichodesmium nitrogen fixation by 2100.

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Towards modelling cold-water coral reef-scale crumbling: including morphological variability in mechanical surrogate models

The structural complexity of cold-water corals is threatened by ocean acidification. Increased porosity and weakening of structurally critical parts of the reef framework may lead to rapid physical collapse on an ecosystem scale, reducing their potential for biodiversity support. We can use computational models to describe the mechanisms leading to reef-crumbling. How-ever, the implementation of such models into an efficient predictive tool that allows us to determine risk and timescales of reef collapse is missing. Here, we identified possible surrogate models to represent the branching architecture of the cold-water coral species Lophelia pertusa. For length scales greater than 13 cm, a continuum finite element mechanical approach can be used to analyse mechanical competence whereas at smaller length scales, mechanical surrogate models need to explicitly account for the statistical differences in the structure. We showed large morphological variations between L. pertusa colonies and branches, as well as dead and live skeletal structures, which need to be considered for the development of rapid monitoring tools for predicting risk of cold-water coral reefs crumbling. This will allow us to investigate timescales of changes, including the impact of exposure times to acidified waters on reef-crumbling.

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Environmental change impacts on shell formation in the muricid Nucella lapillus

Environmental change is a significant threat to marine ecosystems worldwide. Ocean acidification, global warming and long-term emissions of anthropogenic effluents are all negatively impacting aquatic life. Marine calcifying organisms, in particular, are expected to be severely affected by decreasing seawater pH, resulting in shell dissolution and retardations during the formation and repair of shells. Understanding the underlying biological and environmental factors driving species vulnerabilities to habitat alterations is thus crucial to our ability to faithfully predict impacts on marine ecosystems under an array of environmental change scenarios. So far, existing knowledge about organism responses mainly stems from short to medium term laboratory experiments of single species or over- simplified communities. Although these studies have provided important insights, results may not translate to organism responses in a complex natural system requiring a more holistic experimental approach. In this thesis, I investigated shell formation mechanisms and shape and elemental composition responses in the shell of the important intertidal predatory muricid Nucella lapillus both in situ and across heterogeneous environmental gradients. The aim was to identify potential coping mechanisms of N. lapillus to environmental change and provide a more coherent picture of shell formation responses along large ecological gradients in the spatial and temporal domain. To investigate shell formation mechanisms, I tested for the possibility of shell recycling as a function to reduce calcification costs during times of exceptional demand using a multi-treatment shell labelling experiment. Reports on calcification costs vary largely in the literature. Still, recent discoveries showed that costs might increase as a function of decreasing calcification substrate abundance, suggesting that shell formation becomes increasingly more costly under future environmental change scenarios. However, despite the anticipated costs, no evidence was found that would indicate the use of functional dissolution as a means to recycle shell material for a more cost-efficient shell formation in N. lapillus. To investigate shell formation responses, I combined morphometric and shell thickness analyses with novel statistical methods to identify natural shape and thickness response of N. lapillus to large scale variability in temperature, salinity, wind speed and the carbonate system across a wide geographic range (from Portugal to Iceland) and through time (over 130 years). I found that along geographical gradients, the state of the carbonate system and, more specifically, the substrate inhibitor ratio ([HCO3−][H+]−1) (SIR) was the main predictor for shape variations in N. lapillus. Populations in regions with a lower SIR tend to form narrower shells with a higher spire to body whorl ratio. In contrast, populations in regions with a higher SIR form wider shells with a much lower spire to body whorl ratio. The results suggest a widespread phenotypic response of N. lapillus to continuing ocean acidification could be expected, affecting its phenotypic response patterns to predator or wave exposure regimes with profound implications for North Atlantic rocky shore communities. On the contrary, investigations of shell shape and thickness changes over the last 130 years from adjacent sampling regions on the Southern North Sea coast revealed that contrary to global predictions, N. lapillus built continuously thicker shells while maintaining a consistent shell shape throughout the last century. Systematic modelling efforts suggested that the observed shell thickening resulted from higher annual temperatures, longer yearly calcification windows, nearshore eutrophication, and enhanced prey abundance, which mitigated the impact of other climate change factors. An investigation into the trace elemental composition of common pollutant metals in the same archival N. lapillus specimens revealed that shell Cu/Ca and Zn/Ca concentration ratios remained remarkably constant throughout the last 130 years despite substantial shifts in the environmental concentration. However, Pb/Ca concentration ratios showed a definite trend closely aligned with leaded petrol emissions in Europe over the same period. Discussing physiological and environmental drivers for the observed shell bound heavy metal patterns, I argue that, unlike for Pb, constraints on environmental dissolved Cu species abundance and biologically mediated control on internal Zn levels were likely responsible for a decoupling of shell-bound to total ambient Cu and Zn concentrations. The results highlight the complexity of internal and external pathways that govern the uptake of heavy metals into the molluscan shell and suggest that the shell of N. lapillus could be a suitable archive for a targeted investigation of Pb pollution in the intertidal zone.

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Co-occurring anthropogenic stressors reduce the timeframe of environmental viability for the world’s coral reefs

Anthropogenic disturbances are posing unprecedented challenges to the persistence of ecosystems worldwide. The speed at which these disturbances reach an ecosystem’s tolerance thresholds will determine the time available for adaptation and conservation. Here, we aim to calculate the year after which a given environmental stressor permanently exceeds the bounds of an ecosystem’s tolerance. Ecosystem thresholds are here defined as limits in a given stressor beyond which ecosystems have showed considerable changes in community assembly and functioning, becoming remnants of what they once were, but not necessarily leading to species extirpation or extinction. Using the world’s coral reefs as a case example, we show that the projected effects of marine heatwaves, ocean acidification, storms, land-based pollution, and local human stressors are being underestimated considerably by looking at disturbances independently. Given the spatial complementarity in which numerous disturbances impact the world’s coral reefs, we show that the timelines of environmental suitability are halved when all disturbances are analyzed simultaneously, as opposed to independently. Under business-as-usual scenarios, the median year after which environmental conditions become unsuitable for the world’s remaining coral reefs was, at worse, 2050 for any one disturbance alone (28 years left); but when analyzed concurrently, this date was shortened to 2035 (13 years left). When analyzed together, disturbances reduced the date of environmental suitability because areas that may remain suitable under one disturbance could become unsuitable by any of several other variables. The significance of co-occurring disturbances at reducing timeframes of environmental suitability was evident even under optimistic scenarios. The best-case scenario, characterized by strong mitigation of greenhouse gas emissions and optimistic human development, resulted in 41% of global coral reefs with unsuitable conditions by 2100 under any one disturbance independently; yet when analyzed in combination up to 64% of the world’s coral reefs could face unsuitable environmental conditions by one disturbance or another. Under the worst-case scenario, nearly all coral reef ecosystems worldwide (approximately 99%) will permanently face unsuitable conditions by 2055 in at least one of the disturbances analyzed. Prior studies have indicated the projected dire effects of climate change on coral reefs by mid-century; by analyzing a multitude of projected disturbances, our study reveals a much more severe prognosis for the world’s coral reefs as they have significantly less time to adapt while highlighting the urgent need to tackle available solutions to human disturbances.

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Tipping points of marine phytoplankton to multiple environmental stressors

Globally, anthropogenic climate change is threatening marine species. However, whether and how global marine phytoplankton, which represent the base of marine food webs, will exceed their tipping points under multiple climate factors remain unclear. Here, by establishing machine learning models, we identified the tipping points of global marine phytoplankton production and resistance under eight environmental stressors. Phytoplankton production and resistance are affected by multiple factors and the temperature and partial pressure of carbon dioxide dominate the risks for reaching their tipping points. If the current emission scenario continues, 50% (40–61% at 90% confidence) and 41% (2–80% at 90% confidence) of tropical areas would reach the tipping points of ongoing phytoplankton production and resistance decline, respectively, in 2100. Compared with single- or few-factor studies, machine learning (for example, ensemble machine learning) provides a powerful and realistic solution for policy-makers facing large-scale ecological responses to global climate changes under multiple environmental stressors.

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Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine cyanobacterium Synechococcus (Cyanophyceae)

The marine cyanobacterium Synechococcus elongatus was grown in a continuous culture system to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO2 (pCO2) on its growth and physiological characteristics. Cells were grown on a 14:10 h light:dark cycle at all combinations of low and high irradiance (50 and 300 μmol photons ⋅ m−2 ⋅ s−1, respectively), low and high pCO2 (400 and 1000 ppmv, respectively), nutrient limitation (nitrate-limited and nutrient-replete conditions), and temperatures of 20–45°C in 5°C increments. The maximum growth rate was ~4.5 · d−1 at 30–35°C. Under nutrient-replete conditions, growth rates at most temperatures and irradiances were about 8% slower at a pCO2 of 1000 ppmv versus 400 ppmv. The single exception was 45°C and high irradiance. Under those conditions, growth rates were ~45% higher at 1000 ppmv. Cellular carbon:nitrogen ratios were independent of temperature at a fixed relative growth rate but higher at high irradiance than at low irradiance. Initial slopes of photosynthesis–irradiance curves were higher at all temperatures under nutrient-replete versus nitrate-limited conditions; they were similar at all temperatures under high and low irradiance, except at 20°C, when they were suppressed at high irradiance. A model of phytoplankton growth in which cellular carbon was allocated to structure, storage, or the light or dark reactions of photosynthesis accounted for the general patterns of cell composition and growth rate. Allocation of carbon to the light reactions of photosynthesis was consistently higher at low versus high light and under nutrient-replete versus nitrate-limited conditions.

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Pelagic calcifiers face increased mortality and habitat loss with warming and ocean acidification

Global change is impacting the oceans in an unprecedented way, and multiple lines of evidence suggest that species distributions are changing in space and time. There is increasing evidence that multiple environmental stressors act together to constrain species habitat more than expected from warming alone. Here, we conducted a comprehensive study of how temperature and aragonite saturation state act together to limit Limacina helicina, globally distributed pteropods that are ecologically important pelagic calcifiers and an indicator species for ocean change. We co-validated three different approaches to evaluate the impact of ocean warming and acidification (OWA) on the survival and distribution of this species in the California Current Ecosystem. First, we used colocated physical, chemical, and biological data from three large-scale west coast cruises and regional time series; second, we conducted multifactorial experimental incubations to evaluate how OWA impacts pteropod survival; and third, we validated the relationships we found against global distributions of pteropods and carbonate chemistry. OWA experimental work revealed mortality increases under OWA, while regional habitat suitability indices and global distributions of L. helicina suggest that a multi-stressor framework is essential for understanding pteropod distributions. In California Current Ecosystem habitats, where pteropods are living close to their thermal maximum already, additional warming and acidification through unabated fossil fuel emissions (RCP 8.5) are expected to dramatically reduce habitat suitability.

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Impacts of ocean warming and acidification on the energy budget of three commercially important fish species

Using experimental data of three commercially important marine fish species (Diplodus sargus, Diplodus cervinus and Solea senegalensis), a model based on Dynamic Energy Budget theory was parametrized. The model was used to produce projections of growth and reproduction for these species, under different scenarios of ocean warming and acidification.

A mechanistic model based on Dynamic Energy Budget (DEB) theory was developed to predict the combined effects of ocean warming, acidification and decreased food availability on growth and reproduction of three commercially important marine fish species: white seabream (Diplodus sargus), zebra seabream (Diplodus cervinus) and Senegalese sole (Solea senegalensis). Model simulations used a parameter set for each species, estimated by the Add-my-Pet method using data from laboratory experiments complemented with bibliographic sources. An acidification stress factor was added as a modifier of the somatic maintenance costs and estimated for each species to quantify the effect of a decrease in pH from 8.0 to 7.4 (white seabream) or 7.7 (zebra seabream and Senegalese sole). The model was used to project total length of individuals along their usual lifespan and number of eggs produced by an adult individual within one year, under different climate change scenarios for the end of the 21st century. For the Intergovernmental Panel on Climate Change SSP5-8.5, ocean warming led to higher growth rates during the first years of development, as well as an increase of 32-34% in egg production, for the three species. Ocean acidification contributed to reduced growth for white seabream and Senegalese sole and a small increase for zebra seabream, as well as a decrease in egg production of 48-52% and 14-33% for white seabream and Senegalese sole, respectively, and an increase of 4-5% for zebra seabream. The combined effect of ocean warming and acidification is strongly dependent on the decrease of food availability, which leads to significant reduction in growth and egg production. This is the first study to assess the combined effects of ocean warming and acidification using DEB models on fish, therefore, further research is needed for a better understanding of these climate change-related effects among different taxonomic groups and species.

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Climate change will fragment Florida stone crab communities

Many marine species have been shown to be threatened by both ocean acidification and ocean warming which are reducing survival, altering behavior, and posing limits on physiology, especially during earlier life stages. The commercially important Florida stone crab, Menippe mercenaria, is one species that is affected by reduced seawater pH and elevated seawater temperatures. In this study, we determined the impacts of reduced pH and elevated temperature on the distribution of the stone crab larvae along the West Florida Shelf. To understand the dispersion of the larvae, we coupled the multi-scale ocean model SLIM with a larval dispersal model. We then conducted a connectivity study and evaluated the impacts of climate stressors by looking at four different scenarios which included models that represented the dispersion of stone crab larvae under: 1) present day conditions as modelled by SLIM for the temperature and NEMO-PISCES for the pH, 2) SSP1-2.6 scenario (-0.037 reduction in pH and +0.5°C compared to present-day conditions), 3) SSP2-4.5 scenario(-0.15 reduction in pH and +1.5°C) and 4) SSP5-8.5 scenario (-0.375 reduction in pH and +3.5°C). Our results show a clear impact of these climate change stressors on larval dispersal and on the subsequent stone crab distribution. Our results indicate that future climate change could result in stone crabs moving north or into deeper waters. We also observed an increase in the number of larvae settling in deeper waters (defined as the non-fishing zone in this study with depths exceeding 30 m) that are not typically part of the commercial fishing zone. The distance travelled by larvae, however, is likely to decrease, resulting in an increase of self-recruitment and decrease of the size of the sub-populations. A shift of the spawning period, to earlier in the spring, is also likely to occur. Our results suggest that habitats in the non-fishing zone cannot serve as a significant source of larvae for the habitats in the fishing zone (defined as water depth< 30 m) since there is very little exchange (< 5% of all exchanges) between the two zones. These results indicate that the stone crab populations in Florida may be susceptible to community fragmentation and that the management of the fishery should consider the potential impacts of future climate change scenarios.

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Role of coral symbiont in coral resilience under future ocean conditions

Anthropogenic climate change is leading to severe consequences for coral reefs because it disrupts the mutualistic partnership between the coral host and their dinoflagellate endosymbionts (Family: Symbiodiniaceae). Ocean acidification (OA) and ocean warming lead to reduced coral growth, causes coral bleaching, and increases coral mortality. One mechanism of long-term acclimatization to thermal stress by corals is to acquire more thermally tolerant symbiont lineages or increase the proportion of thermally tolerant lineages in the symbiont community. Using a combination of field and long-term mesocosm experiments this research investigated the main drivers of Symbiodiniaceae community composition in some of the main corals in Hawai‘i. The first chapter elucidates the baseline symbiont community composition of 600 colonies of Montipora capitata sampled from 30 reefs across the range of environmental conditions that occur in Kāne‘ohe Bay. Symbiodiniaceae community differed markedly across sites, with M. capitata in the most open-ocean (northern) site hosting few or none of the genus Durusdinium, whereas individuals at other sites had a mix of Durusdinium and Cladocopium. The second chapter then investigates how the symbiont composition of those same individually marked colonies responded to the 2019 bleaching event. The relative proportion of the heat-tolerant symbiont Durusdinium increased in most parts of the bay, but despite this significant increase in abundance, the overall algal symbiont community composition was largely unchanged. Rather than bleaching stress, symbiont community composition was driven by environmentally designated regions across the bay, and remained differentiated and similar to pre-bleaching composition. Among measured variables, depth and variability in temperature were the most significant drivers of Symbiodiniaceae community composition among sites, regardless of bleaching intensity or change in relative proportion of Durusdinium. The final chapter investigates the role of specificity in the symbiont community composition for eight of the main Hawaiian corals sampled from six different locations around O‘ahu. Corals were then maintained for ~2.5 years under temperature and acidification conditions predicted by the end of the century in a mesocosm experiment to determine the response of their symbiont communities to climate change and test for environmental memory. Symbiodiniaceae communities were highly specific in each of the eight coral species-, and site-specific differences in community composition were lost by the end of the experiment in the common garden ambient treatment. Future ocean conditions lead to an increase in stress resilient symbionts (e.g., Durusdinium) in some species, whereas others became more vulnerable to the infection of opportunistic symbionts (e.g., Symbiodinium or Breviolum). Temperature was found to be the main driver of change, whereas there was no significant effect of acidification on symbiont community composition. Provenance of corals mattered, because corals from some locations responded differently than conspecifics from other locations confirming an environmental memory effect. Together these results highlight the complexity in predicting coral response to future ocean conditions. Algal symbiont community composition of corals changes in response to their environment, and that this response is dependent on both the coral species and their site of origin, highlighting the role of symbiont specificity and environmental memory in shaping coral resilience.

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Coupled carbonate chemistry – harmful algae bloom models for studying effects of ocean acidification on Prorocentrum minimum blooms in a eutrophic estuary

Eutrophic estuaries have suffered from a proliferation of harmful algal blooms (HABs) and acceleration of ocean acidification (OA) over the past few decades. Despite laboratory experiments indicating pH effects on algal growth, little is understood about how acidification affects HABs in estuaries that typically feature strong horizontal and vertical gradients in pH and other carbonate chemistry parameters. Here, coupled hydrodynamic–carbonate chemistry–HAB models were developed to gain a better understanding of OA effects on a high biomass HAB in a eutrophic estuary and to project how the global anthropogenic CO2 increase might affect these HABs in the future climate. Prorocentrum minimum in Chesapeake bay, USA, one of the most common HAB species in estuarine waters, was used as an example for studying the OA effects on HABs. Laboratory data on P. minimum grown under different pH conditions were applied in the development of an empirical formula relating growth rate to pH. Hindcast simulation using the coupled hydrodynamic-carbonate chemistry–HAB models showed that the P. minimum blooms were enhanced in the upper bay where pH was low. On the other hand, pH effects on P. minimum growth in the mid and lower bay with higher pH were minimal, but model simulations show surface seaward estuarine flow exported the higher biomass in the upper bay downstream. Future model projections with higher atmospheric pCO2 show that the bay-wide averaged P. minimum concentration during the bloom periods increases by 2.9% in 2050 and 6.2% in 2100 as pH decreases and 0.2 or 0.4, respectively. Overall the model results suggest OA will cause a moderate amplification of P. minimum blooms in Chesapeake bay. The coupled modeling framework developed here can be applied to study the effects of OA on other HAB species in estuarine and coastal environments.

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The Foraminiferal response to climate stressors project: tracking the community response of planktonic Foraminifera to historical climate change

Planktonic Foraminifera are ubiquitous marine protozoa inhabiting the upper ocean. During life, they secrete calcareous shells, which accumulate in marine sediments, providing a geological record of past spatial and temporal changes in their community structure. As a result, they provide the opportunity to analyze both current and historical patterns of species distribution and community turnover in this plankton group on a global scale. The FORCIS project aims to unlock this potential by synthesizing a comprehensive global database of abundance and diversity observations of living planktonic Foraminifera in the upper ocean over more than 100 years starting from 1910. The database will allow for unravelling the impact of multiple global-change stressors acting on planktonic Foraminifera in historical times, using an approach that combines statistical analysis of temporal diversity changes in response to environmental changes with numerical modeling of species response based on their ecological traits.

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