Posts Tagged 'communitymodeling'

Direct and indirect impacts of marine acidification on the ecosystem services provided by coralligenous reefs and seagrass systems

Increasing emissions of CO2 and the resultant ocean acidification (OA) will have large implications for the marine ecosystems sustained by habitat-forming species and their related ecosystem services (ES), with potentially significant impacts on human well-being. Here, we provide an assessment of the direct and indirect impacts of OA on ES. The changes in the functioning of coralligenous reefs and Posidonia oceanica meadows promoted by OA were investigated by i) synthesizing current knowledge into conceptual models. The models were then used to, ii) assessing the impacts of exposure of the selected taxa at the acidification level associated with two CO2 emission scenarios and iii) using the conceptual model outputs to project the cascading impacts from individuals to functions to ES.

The results highlight that the combination of the direct and indirect effects of acidification will alter many functions of both coralligenous and P.oceanica systems, triggering habitat modifications and the loss of highly valuable ES.

While the exact timing of the expected changes will depend on the severity of the emission scenarios, significant and hardly reversible changes can be expected as quickly as a few decades under the business-as-usual scenario, and many ecosystem services are at risk even under much more conservative scenarios.

Continue reading ‘Direct and indirect impacts of marine acidification on the ecosystem services provided by coralligenous reefs and seagrass systems’

Highest plasticity of carbon‐concentrating mechanisms in earliest evolved phytoplankton

Phytoplankton photosynthesis strongly relies on the operation of carbon‐concentrating mechanisms (CCMs) to accumulate CO2 around their carboxylating enzyme ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO). Earlier evolved phytoplankton groups were shown to exhibit higher CCM activities to compensate for their RuBisCO with low CO2 specificities. Here, we tested whether earlier evolved phytoplankton groups also exhibit a higher CCM plasticity. To this end, we collected data from literature and applied a Bayesian linear meta‐analytic model. Our results show that with elevated pCO2, photosynthetic CO2 affinities decreased strongest and most consistent for the earlier evolved groups, i.e., cyanobacteria and dinoflagellates, while CO2‐dependent changes in affinities for haptophytes and diatoms were smaller and less consistent. In addition, responses of maximum photosynthetic rates toward elevated pCO2 were generally small and inconsistent across species. Our results demonstrate that phytoplankton groups with an earlier origin possess a high CCM plasticity, whereas more recently evolved groups do not, which likely results from evolved differences in the CO2 specificity of RuBisCO.

Continue reading ‘Highest plasticity of carbon‐concentrating mechanisms in earliest evolved phytoplankton’

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’

Individual and population level effects of ocean acidification on a predator−prey system with inducible defenses: bryozoan−nudibranch interactions in the Salish Sea

Ocean acidification (OA) from in creased oceanic CO2 concentrations imposes significant physiological stresses on many calcifying organisms. OA effects on individual organisms may be synergistically amplified or reduced by inter- and intraspecies interactions as they propagate up to population and community
levels, altering predictions by studies of calcifier responses in isolation. The calcifying colonial bryozoan Membranipora membranacea and the predatory nudibranch Corambe steinbergae comprise a trophic system strongly regulated by predator induced defensive responses and space limitation, presenting a unique system to investigate OA effects on these regulatory mechanisms at individual and population levels. We experimentally quantified OA effects across a range of pH from 7.0 to 7.9 on growth, calcification, senescence and predator-induced spine formation in Membranipora, with or without waterborne predator cue, and on zooid consumption rates in Corambe at Friday Harbor Laboratories, San Juan Island, WA. Membranipora exhibited maximum growth and calcification at moderately low pH (7.6), and continued spine formation in all pH treatments.
Spines reduced Corambe zooid consumption rates, with lower pH weakening this effect. Using a spatially explicit model of colony growth, where colony area
serves as a proxy for colony fitness, we assessed the population-level impacts of these experimentally determined individual-level effects in the context of
space limitation. The area-based fitness costs associated with defense measured at the individual level led to amplified effects predicted for the population level due to competition. Our coupled experimental and modeling results demonstrate the need to consider population-level processes when assessing ecological responses to stresses from changing environments.

Continue reading ‘Individual and population level effects of ocean acidification on a predator−prey system with inducible defenses: bryozoan−nudibranch interactions in the Salish Sea’

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.

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


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Ocean acidification in the IPCC AR5 WG II

OUP book