Posts Tagged 'communitymodeling'

Modeling impact of varying pH due to carbondioxide on the dynamics of prey–predator species system

In this paper, we have considered a nonlinear mathematical model to investigate the effect of pH on prey–predator dynamics with Holling type II functional response. In the model, capture rate, handling time, growth rate and death rate are considered to be pH dependent. From the analysis of the model, it has been observed that as pH level goes below the normal tolerance limit of prey species then the equilibrium density of prey population decreases due to increase in capture rate and decrease in handling time by predator. Further, we have shown that as the growth rate of prey population decreases due to lowering of pH then the density of predator population also decreases and both the populations may tend to extinction if growth rate of prey population becomes negative due to lowering of pH on account of elevated carbondioxide concentration in the aquatic body. Moreover, it is noticed from the simulation that if the mortality of predator population increases because of decrease in pH level then the prey population gets advantage and in-turn their population increases.

Continue reading ‘Modeling impact of varying pH due to carbondioxide on the dynamics of prey–predator species system’

Microzooplankton grazing responds to simulated ocean acidification indirectly through changes in prey cellular characteristics

Microzooplankton (MZP) grazing is a factor that regulates oceanic primary production and is a controlling mechanism for marine biogeochemical cycling. Despite the prominent ecological role of MZP, few studies have explored their responses to ocean acidification (OA). Studies to date generally indicate that MZP are affected indirectly by OA through changes in phytoplankton prey composition and biomass concentration. Here, we conducted a series of experiments testing whether OA-induced changes in cellular characteristics of individual prey species can cause changes in MZP grazing. Two tintinnid ciliates (Eutintinnus sp. and Schmidingerella sp.) and a heterotrophic dinoflagellate (Oxyrrhis marina) were offered phytoplankton prey (Emiliania huxleyi) cultured under 3 pCO2 concentrations. Using linear mixed effects models, we found that Eutintinnus sp. and O. marina exhibited a step-wise increase in ingestion rates on E. huxleyi cells cultured under elevated pCO2. Schmidingerella sp. ingestion showed a non-linear response, whereby cells cultured under high pCO2 were ingested at higher rates than cells from moderate pCO2. The percentages of all 3 MZP populations observed feeding were higher on E. huxleyi cells cultured under elevated pCO2, with Eutintinnus sp. showing a step-wise increase. We postulate that this response is caused by the observed increased coccosphere volume in E. huxleyi cells cultured under elevated pCO2. If changes in phytoplankton cell volume are widespread under OA, this could be an important mechanism by which MZP grazing behavior shifts and planktonic food web dynamics are altered in the future ocean.

Continue reading ‘Microzooplankton grazing responds to simulated ocean acidification indirectly through changes in prey cellular characteristics’

Projected amplification of food web bioaccumulation of MeHg and PCBs under climate change in the Northeastern Pacific

Climate change increases exposure and bioaccumulation of pollutants in marine organisms, posing substantial ecophysiological and ecotoxicological risks. Here, we applied a trophodynamic ecosystem model to examine the bioaccumulation of organic mercury (MeHg) and polychlorinated biphenyls (PCBs) in a Northeastern Pacific marine food web under climate change. We found largely heterogeneous sensitivity in climate-pollution impacts between chemicals and trophic groups. Concentration of MeHg and PCBs in top predators, including resident killer whales, is projected to be amplified by 8 and 3%, respectively, by 2100 under a high carbon emission scenario (Representative Concentration Pathway 8.5) relative to a no-climate change control scenario. However, the level of amplification increases with higher carbon emission scenario for MeHg, but decreases for PCBs. Such idiosyncratic responses are shaped by the differences in bioaccumulation pathways between MeHg and PCBs, and the modifications of food web dynamics between different levels of climate change. Climate-induced pollutant amplification in mid-trophic level predators (Chinook salmon) are projected to be higher (~10%) than killer whales. Overall, the predicted trophic magnification factor is ten-fold higher in MeHg than in PCBs under high CO2 emissions. This contribution highlights the importance of understanding the interactions with anthropogenic organic pollutants in assessing climate risks on marine ecosystems.

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Global change in marine aquaculture production potential under climate change

Climate change is an immediate and future threat to food security globally. The consequences for fisheries and agriculture production potential are well studied, yet the possible outcomes for aquaculture (that is, aquatic farming)—one of the fastest growing food sectors on the planet—remain a major gap in scientific understanding. With over one-third of aquaculture produced in marine waters and this proportion increasing, it is critical to anticipate new opportunities and challenges in marine production under climate change. Here, we model and map the effect of warming ocean conditions (Representative Concentration Pathway scenario 8.5) on marine aquaculture production potential over the next century, based on thermal tolerance and growth data of 180 cultured finfish and bivalve species. We find heterogeneous patterns of gains and losses, but an overall greater probability of declines worldwide. Accounting for multiple drivers of species growth, including shifts in temperature, chlorophyll and ocean acidification, reveals potentially greater declines in bivalve aquaculture compared with finfish production. This study addresses a missing component in food security research and sustainable development planning by identifying regions that will face potentially greater climate change challenges and resilience with regards to marine aquaculture in the coming decades. Understanding the scale and magnitude of future increases and reductions in aquaculture potential is critical for designing effective and efficient use and protection of the oceans, and ultimately for feeding the planet sustainably.

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Opportunities for climate‐risk reduction through effective fisheries management

Risk of impact of marine fishes to fishing and climate change (including ocean acidification) depend on the species’ ecological and biological characteristics, as well as their exposure to over‐exploitation and climate hazards. These human‐induced hazards should be considered concurrently in conservation risk assessment. In this study, we aim to examine the combined contributions of climate change and fishing to the risk of impacts of exploited fishes, and the scope for climate‐risk reduction from fisheries management. We combine fuzzy logic expert system with species distribution modeling to assess the extinction risks of climate and fishing impacts of 825 exploited marine fish species across the global ocean. We compare our calculated risk index with extinction risk of marine species assessed by the International Union for Conservation of Nature (IUCN). Our results show that 60% (499 species) of the assessed species are projected to experience very high risk from both overfishing and climate change under a “business‐as‐usual” scenario (RCP 8.5 with current status of fisheries) by 2050. The risk index is significantly and positively related to level of IUCN extinction risk (ordinal logistic regression, p < 0.0001). Furthermore, the regression model predicts species with very high risk index would have at least one in five (>20%) chance of having high extinction risk in the next few decades (equivalent to the IUCN categories of vulnerable, endangered or critically endangered). Areas with more at‐risk species to climate change are in tropical and subtropical oceans, while those that are at risk to fishing are distributed more broadly, with higher concentration of at‐risk species in North Atlantic and South Pacific Ocean. The number of species with high extinction risk would decrease by 63% under the sustainable fisheries‐low emission scenario relative to the “business‐as‐usual” scenario. This study highlights the substantial opportunities for climate‐risk reduction through effective fisheries management.

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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.

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


• 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.


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’

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Ocean acidification in the IPCC AR5 WG II

OUP book