Posts Tagged 'communitymodeling'

Model assessment and model-based data analyses of an ocean acidification mesocosm experiment

Ocean acidification (OA) has been dubbed as the “evil twin” of climate change. Studies suggest that OA has dramatic impacts on marine phytoplankton. Mesocosm facilities allow investigations on effects of changes in the carbonate chemistry of sea water on plankton communities in the vicinity of their natural habitats, e.g. Pelagic ecosystem CO2 enrichment (PeECE) studies. Marine ecosystem models serve as an efficient tool to analyse and interpret mesocosm data, as they use mathematical equations to describe processes controlling dynamics of planktonic ecosystems. The goal of this thesis is to investigate the effects of OA on phytoplankton growth dynamics by analysing data from an ocean acidification mesocosm experiment using different model approaches. To achieve this data assimilation (DA) methods are applied. These methods yield the optimised model solutions (with optimised parameter values) that maximize the likelihood probability of models explaining mesocosm data. In addition, DA methods estimate the ranges of uncertainty in optimised model parameter values. In the first study (Chapter 2), the performance of different metrics (cost functions) that maximize the predictive capability of a plankton model are evaluated. Next, an optimality-based model is applied to investigate the large observed variability in calcification and total alkalinity during the PeECE-I experiment (Chapter 3). The model considers an explicit CO2 dependency of calcification. Three model experiments are set up to simulate growth of bulk phytoplankton and coccolithophores in mesocosms with high, medium and low observed calcification rates. Skills of two plankton models (OBM and CN-REcoM) that differ in their mechanistic description of nutrient uptake and algal growth are assessed against mesocosm data in the last study (Chapter 4) of this thesis. In contrast to the calcification study, the plankton models that are applied in Chapter 4 do not resolve any CO2 effects on phytoplankton growth dynamics. The idea is to test whether this neglect of CO2 dependencies is revealed in differences of model parameter estimates between different CO2 treatments. According to DA results, the cost function that is derived from a probabilistic approach and accounts for changes in correlations between observations performs better as metric for model calibration than other types of cost functions (e.g. Root mean squared errors). The model-based data analysis of the PeECE-I experiment suggests that the large variability that was observed in calcification could have been generated due to small differences in initial abundance of coccolithophores during initialisation (filling) of mesocosms. A pattern is seen in the estimates of two physiological parameters, the potential carbon fixation rate (V C 0 ) and the subsistence quota (Qmin), between the CO2 treatments for the OBM. It predicts high estimates of V C 0 and Qmin for phytoplankton in mesocosms treated with high CO2 concentrations and vice versa for those in mesocosms with low CO2. The OBM seems to suggest that OA may enhance carbon fixation rates in phytoplankton, but at the cost of elevated metabolic stress. However, it is suggested to include mechanistic CO2 dependencies of nutrient uptake and phytoplankton growth in the OBM for future studies on OA.

Continue reading ‘Model assessment and model-based data analyses of an ocean acidification mesocosm experiment’

Comparing model parameterizations of the biophysical impacts of ocean acidification to identify limitations and uncertainties

Highlights

• We explored model approaches for ocean acidification effects on marine organisms.
• Modelled effects on aerobic performance were scaled up to population level dynamics.
• Results were sensitive to model structure, then scenario and parameter uncertainty.
• Sensitivity was variable across species and the source of uncertainty.
• Integrated global change models progress development of future scenarios.

Abstract

Ocean acidification (OA) driven by anthropogenic CO2 emissions affects marine ecosystems, fisheries and aquaculture. Assessing the impacts of OA using projection models facilitates the development of future scenarios and potential solutions. Here, we explored various ways to incorporate OA impacts into a multi-stressor dynamic bioclimatic envelope model to project biogeographic changes of ten commercially exploited invertebrate species. We examine three dimensions of uncertainties in modelling biophysical OA effects: model structure, parameterization, and scenario uncertainty. Our results show that projected OA impacts are most sensitive to the choice of structural relationship between OA and biological responses, followed by the choice of climate change emission scenarios and parameterizations of the size of OA effects. Species generally showed negative effects to OA but sensitivity to the various sources of uncertainty were not consistent across or within species. For example, some species showed higher sensitivity to structural uncertainty and very low sensitivity to parameter uncertainty, while others showed greatest sensitivity to parameter uncertainty. This variability is largely due to geographic variability and difference in life history traits used to parameterize model simulations. Our model highlights the variability across the sources of uncertainty and contributes to the development of integrating OA impacts in species distribution models. We further stress the importance of defining the limitations and assumptions, as well as exploring the range of uncertainties associated with modelling OA impacts.

Continue reading ‘Comparing model parameterizations of the biophysical impacts of ocean acidification to identify limitations and uncertainties’

A three-dimensional niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica: reconciling observations with projections (update)

Coccolithophore responses to changes in carbonate chemistry speciation such as CO2 and H+ are highly modulated by light intensity and temperature. Here, we fit an analytical equation, accounting for simultaneous changes in carbonate chemistry speciation, light and temperature, to published and original data for Emiliania huxleyi, and compare the projections with those for Gephyrocapsa oceanica. Based on our analysis, the two most common bloom-forming species in present-day coccolithophore communities appear to be adapted for a similar fundamental light niche but slightly different ones for temperature and CO2, with E. huxleyi having a tolerance to lower temperatures and higher CO2 levels than G. oceanica. Based on growth rates, a dominance of E. huxleyi over G. oceanica is projected below temperatures of 22 °C at current atmospheric CO2 levels. This is similar to a global surface sediment compilation of E. huxleyi and G. oceanica coccolith abundances suggesting temperature-dependent dominance shifts. For a future Representative Concentration Pathway (RCP) 8.5 climate change scenario (1000 µatm fCO2), we project a CO2 driven niche contraction for G. oceanica to regions of even higher temperatures. However, the greater sensitivity of G. oceanica to increasing CO2 is partially mitigated by increasing temperatures. Finally, we compare satellite-derived particulate inorganic carbon estimates in the surface ocean with a recently proposed metric for potential coccolithophore success on the community level, i.e. the temperature-, light- and carbonate-chemistry-dependent CaCO3 production potential (CCPP). Based on E. huxleyi alone, as there was interestingly a better correlation than when in combination with G. oceanica, and excluding the Antarctic province from the analysis, we found a good correlation between CCPP and satellite-derived particulate inorganic carbon (PIC) with an R2 of 0.73, p < 0.01 and a slope of 1.03 for austral winter/boreal summer and an R2 of 0.85, p < 0.01 and a slope of 0.32 for austral summer/boreal winter.

Continue reading ‘A three-dimensional niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica: reconciling observations with projections (update)’

Consequences of spatially variable ocean acidification in the California Current: lower pH drives strongest declines in benthic species in southern regions while greatest economic impacts occur in northern regions

Highlights

• Impacts of ocean acidification change with latitude in the California Current.
• Vulnerable species (e.g., calcifying invertebrates) and their predators decline most.
• Decline in revenue projected, mainly from lower Dungeness crab catch in the north.
Abstract

Marine ecosystems are experiencing rapid changes driven by anthropogenic stressors which, in turn, are affecting human communities. One such stressor is ocean acidification, a result of increasing carbon emissions. Most research on biological impacts of ocean acidification has focused on the responses of an individual species or life stage. Yet, understanding how changes scale from species to ecosystems, and the services they provide, is critical to managing fisheries and setting research priorities. Here we use an ecosystem model, which is forced by oceanographic projections and also coupled to an economic input-output model, to quantify biological responses to ocean acidification in six coastal regions from Vancouver Island, Canada to Baja California, Mexico and economic responses at 17 ports on the US west coast. This model is intended to explore one possible future of how ocean acidification may influence this coastline. Outputs show that declines in species biomass tend to be larger in the southern region of the model, but the largest economic impacts on revenue, income and employment occur from northern California to northern Washington State. The economic consequences are primarily driven by declines in Dungeness crab from loss of prey. Given the substantive revenue generated by the fishing industry on the west coast, the model suggests that long-term planning for communities, researchers and managers in the northern region of the California Current would benefit from tracking Dungeness crab productivity and potential declines related to pH.

Continue reading ‘Consequences of spatially variable ocean acidification in the California Current: lower pH drives strongest declines in benthic species in southern regions while greatest economic impacts occur in northern regions’

The economic impacts of ocean acidification on shellfish fisheries and aquaculture in the United Kingdom

Highlights

• We estimate both direct and economy-wide economic losses of shellfish production by 2100 in UK.
• Direct potential losses due to reduced shellfish production range from 14% to 28% of fishery NPV.
• Total loss to the UK economy from shellfish production and consumption range from £23 – £88 million.
• There are regional variations to economic losses due to different speceis and patterns of shellfish production and consumption.

Abstract

Ocean acidification may pose a major threat to commercial fisheries, especially those for calcifying shellfish species. This study was undertaken to estimate the potential economic costs resulting from ocean acidification on UK wild capture and aquaculture shellfish production. Applying the net present value (NPV) and partial equilibrium (PE) models, we estimate both direct and economy-wide economic losses of shellfish production by 2100. Estimates using the NPV method show that the direct potential losses due to reduced shellfish production range from 14% to 28% of fishery NPV. This equates to annual economic losses of between ö3 and ö6 billion of the UK’s GDP in 2013, for medium and high emission scenarios. Results using the PE model showed the total loss to the UK economy from shellfish production and consumption ranging from ö23–ö88 million. The results from both the direct valuation and predicted estimate for the economic losses on shellfish harvest indicate that there are regional variations due to different patterns of shellfish wild-capture and aquaculture, and the exploitation of species with differing sensitivities to ocean acidification. These results suggest that the potential economic losses vary depending on the chosen valuation method. This analysis is also partial as it did not include a wider group of species in early-life-stages or predator-prey effects. Nevertheless, findings show that the economic losses to the UK and its devolved administrations due to ocean acidification could be substantial. We conclude that addressing ocean acidification with the aim of preserving commercially valuable shellfish resources will require regional, national or international solutions using a combined approach to reduce atmospheric CO2 emissions and shift in focus to exploit species that are less vulnerable to ocean acidification.

Continue reading ‘The economic impacts of ocean acidification on shellfish fisheries and aquaculture in the United Kingdom’

Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean

Highlights

• In a future scenario, attenuation by DOM outcompetes its physico-chemical role.
• Global change conditions will favor growth and photosynthesis of nanoplankton.
• Global change favors growth and photosynthesis of nano- as compared to microplankton.

Abstract

We evaluated the dual role of DOM (i.e., as a source of inorganic nutrients and as an absorber of solar radiation) on a phytoplankton community of the western South Atlantic Ocean. Using a combination of microcosms and a cluster approach, we simulated the future conditions of some variables that are highly influenced by global change in the region. We increased nutrients (i.e., anthropogenic input) and dissolved organic matter (DOM), and we decreased the pH, to assess their combined impact on growth rates (μ), species composition/abundance and size structure, and photosynthesis (considering in this later also the effects of light quality i.e., with and without ultraviolet radiation). We simulated two Future conditions (Fut) where nutrients and pH were similarly manipulated, but in one the physical role of DOM (Futout) was assessed whereas in the other (Futin) the physico-chemical role was evaluated; these conditions were compared with a control (Present condition, Pres). The μ significantly increased in both Fut conditions as compared to the Pres, probably due to the nutrient addition and acidification in the former. The highest μ were observed in the Futout, due to the growth of nanoplanktonic flagellates and diatoms. Cells in the Futin were photosynthetically less efficient as compared to those of the Futout and Pres, but these physiological differences, also between samples with or without solar UVR observed at the beginning of the experiment, decreased with time hinting for an acclimation process. The knowledge of the relative importance of both roles of DOM is especially important for coastal areas that are expected to receive higher inputs and will be more acidified in the future.

Continue reading ‘Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean’

Seagrass habitat metabolism increases short-term extremes and long-term offset of CO2 under future ocean acidification

The role of rising atmospheric CO2 in modulating estuarine carbonate system dynamics remains poorly characterized, likely due to myriad processes driving the complex chemistry in these habitats. We reconstructed the full carbonate system of an estuarine seagrass habitat for a summer period of 2.5 months utilizing a combination of time-series observations and mechanistic modeling, and quantified the roles of aerobic metabolism, mixing, and gas exchange in the observed dynamics. The anthropogenic CO2 burden in the habitat was estimated for the years 1765–2100 to quantify changes in observed high-frequency carbonate chemistry dynamics. The addition of anthropogenic CO2 alters the thermodynamic buffer factors (e.g., the Revelle factor) of the carbonate system, decreasing the seagrass habitat’s ability to buffer natural carbonate system fluctuations. As a result, the most harmful carbonate system indices for many estuarine organisms [minimum pHT, minimum Ωarag, and maximum pCO2(s.w.)] change up to 1.8×, 2.3×, and 1.5× more rapidly than the medians for each parameter, respectively. In this system, the relative benefits of the seagrass habitat in locally mitigating ocean acidification increase with the higher atmospheric CO2 levels predicted toward 2100. Presently, however, these mitigating effects are mixed due to intense diel cycling of CO2 driven by aerobic metabolism. This study provides estimates of how high-frequency pHT, Ωarag, and pCO2(s.w.) dynamics are altered by rising atmospheric CO2 in an estuarine habitat, and highlights nonlinear responses of coastal carbonate parameters to ocean acidification relevant for water quality management.

Continue reading ‘Seagrass habitat metabolism increases short-term extremes and long-term offset of CO2 under future ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

OUP book