Posts Tagged 'communitymodeling'

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’

Modeling alternative stable states in Caribbean coral reefs

1. Abstract

The resilience of Caribbean coral reefs, which are an important source of biodiversity and provide essential ecosystem services, is constantly challenged by many reef stressors including ocean acidification, hurricane damage, and overharvesting of herbivorous reef fish. The presence of two alternative stable states—a desirable state with high levels of coral cover and its coral‐depleted counterpart—has been widely documented in the literature. Increasing coral resilience to prevent phase shifts to the undesirable state is a critical research priority, and mathematical models can serve as an important tool to not only better understand the underlying dynamics of observed coral communities, but also to evaluate the potential impacts of stressors and the outcome of management strategies designed to promote coral persistence. Here, we review the existing literature of mathematical models designed to understand the processes that generate alternative stable states. We focus on models that are comprised of ordinary differential equations and, at their core, capture algal–coral dynamics.

2. Recommendations for resource managers

Evidence for the existence of alternative stable states and the associated presence of hysteresis implies a need for management designed to increase the resilience of coral reef ecosystems.

In addition, holistic approaches to designing management strategies are required to both increase resilience of coral reefs and maximize the benefits of the ecosystem services they provide.

Due to the intrinsic complexity and spatial variability of coral reef ecosystems, management cannot be designed using a “one size fits all” approach. Instead, local dynamics and stressors need to be carefully considered. Continue reading ‘Modeling alternative stable states in Caribbean coral reefs’

Climate change alters fish community size‐structure, requiring adaptive policy targets

Size‐based indicators are used worldwide in research that supports the management of commercially exploited wild fish populations, because of their responsiveness to fishing pressure. Observational and experimental data, however, have highlighted the deeply rooted links between fish size and environmental conditions that can drive additional, interannual changes in these indicators. Here, we have used biogeochemical and mechanistic niche modelling of commercially exploited demersal fish species to project time series to the end of the 21st century for one such indicator, the large fish indicator (LFI), under global CO2 emissions scenarios. Our modelling results, validated against survey data, suggest that the LFI’s previously proposed policy target may be unachievable under future climate change. In turn, our results help to identify what may be achievable policy targets for demersal fish communities experiencing climate change. While fisheries modelling has grown as a science, climate change modelling is seldom used specifically to address policy aims. Studies such as this one can, however, enable a more sustainable exploitation of marine food resources under changes unmanageable by fisheries control. Indeed, such studies can be used to aid resilient policy target setting by taking into account climate‐driven effects on fish community size‐structure.

Continue reading ‘Climate change alters fish community size‐structure, requiring adaptive policy targets’

The future of fishes and fisheries in the changing oceans

This paper aims to highlight the risk of climate change on coupled marine human and natural systems and explore possible solutions to reduce such risk. Specifically, it explores some of the key responses of marine fish stocks and fisheries to climate change and their implications for human society. It highlights the importance of mitigating carbon emission and achieving the Paris Agreement in reducing climate risk on marine fish stocks and fisheries. Finally, it discusses potential opportunities for helping fisheries to reduce climate threats, through local adaptation. A research direction in fish biology and ecology is proposed that would help support the development of these potential solutions.

Continue reading ‘The future of fishes and fisheries in the changing oceans’

A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change

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 abundant coccolithophores in today’s oceans 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 RCP 8.5 climate change scenario (1000 μatm fCO2 and +4.8 °C) we project a niche contraction for G. oceanica then being restricted to regions of even higher 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). Excluding the Antarctic province from the analysis we found a good correlation between CCPP and satellite derived PIC in the other regions with an R2 of 0.73 for Austral winter/Boreal summer and 0.85 for Austral summer/Boreal winter.

Continue reading ‘A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change’

Ocean futures under ocean acidification, marine protection, and changing fishing pressures explored using a worldwide suite of ecosystem models

Ecosystem-based management (EBM) of the ocean considers all impacts on and uses of marine and coastal systems. In recent years, there has been a heightened interest in EBM tools that allow testing of alternative management options and help identify tradeoffs among human uses. End-to-end ecosystem modeling frameworks that consider a wide range of management options are a means to provide integrated solutions to the complex ocean management problems encountered in EBM. Here, we leverage the global advances in ecosystem modeling to explore common opportunities and challenges for ecosystem-based management, including changes in ocean acidification, spatial management, and fishing pressure across eight Atlantis (atlantis.cmar.csiro.au) end-to-end ecosystem models. These models represent marine ecosystems from the tropics to the arctic, varying in size, ecology, and management regimes, using a three-dimensional, spatially-explicit structure parametrized for each system. Results suggest stronger impacts from ocean acidification and marine protected areas than from altering fishing pressure, both in terms of guild-level (i.e., aggregations of similar species or groups) biomass and in terms of indicators of ecological and fishery structure. Effects of ocean acidification were typically negative (reducing biomass), while marine protected areas led to both “winners” and “losers” at the level of particular species (or functional groups). Changing fishing pressure (doubling or halving) had smaller effects on the species guilds or ecosystem indicators than either ocean acidification or marine protected areas. Compensatory effects within guilds led to weaker average effects at the guild level than the species or group level. The impacts and tradeoffs implied by these future scenarios are highly relevant as ocean governance shifts focus from single-sector objectives (e.g., sustainable levels of individual fished stocks) to taking into account competing industrial sectors’ objectives (e.g., simultaneous spatial management of energy, shipping, and fishing) while at the same time grappling with compounded impacts of global climate change (e.g., ocean acidification and warming)

Continue reading ‘Ocean futures under ocean acidification, marine protection, and changing fishing pressures explored using a worldwide suite of ecosystem models’


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Ocean acidification in the IPCC AR5 WG II

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