Posts Tagged 'review'

The challenges of detecting and attributing ocean acidification impacts on marine ecosystems

A substantial body of research now exists demonstrating sensitivities of marine organisms to ocean acidification (OA) in laboratory settings. However, corresponding in situ observations of marine species or ecosystem changes that can be unequivocally attributed to anthropogenic OA are limited. Challenges remain in detecting and attributing OA effects in nature, in part because multiple environmental changes are co-occurring with OA, all of which have the potential to influence marine ecosystem responses. Furthermore, the change in ocean pH since the industrial revolution is small relative to the natural variability within many systems, making it difficult to detect, and in some cases, has yet to cross physiological thresholds. The small number of studies that clearly document OA impacts in nature cannot be interpreted as a lack of larger-scale attributable impacts at the present time or in the future but highlights the need for innovative research approaches and analyses. We summarize the general findings in four relatively well-studied marine groups (seagrasses, pteropods, oysters, and coral reefs) and integrate overarching themes to highlight the challenges involved in detecting and attributing the effects of OA in natural environments. We then discuss four potential strategies to better evaluate and attribute OA impacts on species and ecosystems. First, we highlight the need for work quantifying the anthropogenic input of CO2 in coastal and open-ocean waters to understand how this increase in CO2 interacts with other physical and chemical factors to drive organismal conditions. Second, understanding OA-induced changes in population-level demography, potentially increased sensitivities in certain life stages, and how these effects scale to ecosystem-level processes (e.g. community metabolism) will improve our ability to attribute impacts to OA among co-varying parameters. Third, there is a great need to understand the potential modulation of OA impacts through the interplay of ecology and evolution (eco–evo dynamics). Lastly, further research efforts designed to detect, quantify, and project the effects of OA on marine organisms and ecosystems utilizing a comparative approach with long-term data sets will also provide critical information for informing the management of marine ecosystems.

Continue reading ‘The challenges of detecting and attributing ocean acidification impacts on marine ecosystems’

Vulnerability and resilience of tropical coastal ecosystems to ocean acidification

Ocean acidification leads to a wide variety of responses from tropical coastal ecosystems. Coral reefs are most vulnerable with most coral species exhibiting declining calcification rates with decreasing pH and carbonate chemistry parameters. Some corals show resilience to acidification likely due to active physiological regulation of their calcifying fluid. Other calcifying organisms, such as some foraminifera and coccolithophores, exhibit negative responses, whereas some symbiont-bearing calcifiers respond positively, to increasing acidification. Seagrasses and brown macroalgae thrive under acidified conditions, with increasing rates of primary productivity. Some tropical coastal fish species are resilient, and in some species, respond positively, to acidification. Some tropical species show complex, nonlinear responses to declining pH and carbonate chemistry. Factors that influence the ability of a species to adapt to and/or resist acidification include food supply, nutrient availability, temperature, diet, interactions with symbionts and other organisms and species and community diversity. Interactive effects of ocean acidification with other climate change parameters, such as elevated temperature, play an important but poorly understood role in determining the resilience and vulnerability of tropical coastal species, communities and ecosystems. Some short-lived species can undergo acclimation and/or adaptive evolution to increase fitness in the face of acidification. Biota living in tropical estuarine and nearshore environments, such as mangroves, seagrasses and intertidal and subtidal inshore benthos, are unlikely to be significantly affected by future acidification as such environments exhibit very wide variations in water and sediment pH and carbonate chemistry. Nearly all tropical coastal environments exhibit significant CO2 efflux to the atmosphere due to pCO2 and [CO32-] oversaturation caused by high rates of respiration and factors linked to fluvial discharge. Except for coral reefs, most calcifying organisms and upwelling regions, tropical estuarine and inshore ecosystems unaffected by eutrophication and other anthropogenic problems should be resilient to future acidification.

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Physiological and ecotoxicological interactions of copper and ocean acidification in the polychaete worms Hediste diversicolor and Alitta virens

For coastal aquatic habitats the change in seawater pH occurring as a result of ocean acidification has the potential to alter the speciation and toxicity of the many contaminants that remain in high concentrations in coastal systems. Of particular concern are metals, such as copper, whose speciation is pH sensitive within the OA range. A meta-analysis of studies to date investigating OA-contaminant interactions using marine invertebrates reveals that 72% of the 44 studies conducted have indeed focused on metals such as copper, with only a few studies looking at polycyclic aromatic hydrocarbons (PAH) and pharmaceuticals. No clear trends in the pH-effect size on contaminant toxicity for either species or contaminant group were present however, suggesting species specific physiological responses may influence this interaction as well as contaminant chemistry. A relatively understudied group were the polychaetes, a key functional group for many coastal sediments. Sediments act as a sink for contaminants where they can accumulate to high concentrations. Hence there is high potential for polychaetes to experience elevated metal exposures under reduced seawater pH as OA progresses. To address this knowledge gap, the responses of two common coastal polychaete, Alitta virens and Hediste diversicolor, were studied under three different experimental scenarios (both water-borne and sediment based) focusing on the physiological and toxicological responses under combined exposures to ocean acidification and copper. Water-borne exposures of Alitta virens to 0.25 μM copper under ambient seawater (pH 8.10) showed a significant increase in DNA damage, along with a rise in both SOD activity and lipid peroxidation. However, when exposed to copper under OA conditions (pH 7.70) there was no further increase in DNA damage and a significant decrease in SOD activity was observed alongside a fall in lipid peroxidation suggesting that OA looks to buffer the toxicity responses to this species. This is in contrast to previous studies using mussels and sea urchins, where copper toxicity responses were significantly higher when exposed under OA conditions. To assess whether local adaptations to high levels of copper contamination influences this OA-copper interaction, a population comparison using a metal resistance population of the harbour ragworm, Hediste diversicolor and a nearby non-resistant population was then conducted. Exposures were run using copper concentrations that elicit comparable toxicity responses, using 0.50 uM copper for the resistant population, compared to 0.25 uM for the non-resistant population, reflecting the two-fold differences in LC50 values for these population. These experiments reveal a significant increase by 19.70% in metabolic rate effect size (the combined stressor when compared to the control) in the resistant population compared to a decrease by 24.02% the non-resistant population, along with differences in ammonia excretion rate and the O:N ratio, thus revealing an energetic cost of this genetic resistance when faced with the combined stressors of OA and copper. These data are in line with the emerging energy limited tolerance to stressors’ hypothesis which states that tolerance to stress can be energy limited, with bioenergetics playing a central role in the tolerance to environmental stress. Finally, a more environmentally realistic exposure scenario was conducted using Alitta virens to test the influence of sediment and tidal cycles on worm acid-base and oxidative stress responses. Field measurements of sediment pH revealed that the pHNBS range over a tidal cycle varies from 6.97 to 7.87, indicating that polychaetes are already experiencing pH’s lower than the predictions for near future open oceans. In aquarium exposures, with overlying water of pHNBS 8.10, sediment pHNBS remained within the range of 7.45 to 7.31, when the overlying water was manipulated to OA conditions (pHNBS 7.70) sediment pHNBS was within the same range as the ambient treatment. The lack of change in sediment pH, despite a 0.40 unit drop in seawater pH, removed any comparative differences in physiological and toxicity end points in the worms between treatments. Tidal emersion induced a slight reduction in sediment pH, with a significant copper effect on sediment pH causing a further decrease in pH levels. Interestingly emersion resulted in a significant OA-copper interaction for coelomic fluid bicarbonate, which increased over the emersion period, however, there was no emersion driven acidosis within coelomic fluid. Overall this work further points to contaminant-OA interactions being species specific driven, in part driven by animal physiology. It also highlights the importance of environmentally relevant exposures with sediment dwelling organisms experiencing lower pH levels than the overlying seawater which could potentially affect metal speciation and could lead to OA-contaminant interactions occurring very differently in this environment. These are important considerations for ecotoxicology studies in the face of global ocean changes.

Continue reading ‘Physiological and ecotoxicological interactions of copper and ocean acidification in the polychaete worms Hediste diversicolor and Alitta virens’

A meta-analysis of multiple stressors on seagrasses in the context of marine spatial cumulative impacts assessment

Humans are placing more strain on the world’s oceans than ever before. Furthermore, marine ecosystems are seldom subjected to single stressors, rather they are frequently exposed to multiple, concurrent stressors. When the combined effect of these stressors is calculated and mapped through cumulative impact assessments, it is often assumed that the effects are additive. However, there is increasing evidence that different combinations of stressors can have non-additive impacts, potentially leading to synergistic and unpredictable impacts on ecosystems. Accurately predicting how stressors interact is important in conservation, as removal of certain stressors could provide a greater benefit, or be more detrimental than would be predicted by an additive model. Here, we conduct a meta-analysis to assess the prevalence of additive, synergistic, and antagonistic stressor interaction effects using seagrasses as case study ecosystems. We found that additive interactions were the most commonly reported in seagrass studies. Synergistic and antagonistic interactions were also common, but there was no clear way of predicting where these non-additive interactions occurred. More studies which synthesise the results of stressor interactions are needed to be able to generalise interactions across ecosystem types, which can then be used to improve models for assessing cumulative impacts.

Continue reading ‘A meta-analysis of multiple stressors on seagrasses in the context of marine spatial cumulative impacts assessment’

Universal response pattern of phytoplankton growth rates to increasing CO2

Phytoplankton growth rate is a key variable controlling species succession and ecosystem structure throughout the surface ocean. Carbonate chemistry conditions are known to influence phytoplankton growth rates but there is no conceptual framework allowing us to compare growth rate responses across taxa. Here we analyse the literature to show that phytoplankton growth rates follow an optimum curve response pattern whenever the tested species is exposed to a sufficiently large gradient in proton (H+) concentrations. Based on previous findings with coccolithophores and diatoms, we argue that this “universal reaction norm” is shaped by the stimulating influence of increasing inorganic carbon substrate (left side of the optimum) and the inhibiting influence of increase H+ (right side of the optimum). We envisage that exploration of carbonate chemistry‐dependent optimum curves as a default experimental approach will boost our mechanistic understanding of phytoplankton responses to ocean acidification, like temperature curves have already boosted our mechanistic understanding to global warming.

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Future acidification of the Baltic Sea – A sensitivity study


• Sensitivity of pH and the carbonate system to potential future changes in the Baltic Sea

• pH response to future atmospheric CO2, climate change, and changes in the catchment

• CO2-induced acidification can be enhanced or mitigated by other processes in coastal seas.

• Unlikely that acidification of the Baltic Sea can be counteracted unless CO2 emissions decline


Future acidification of coastal seas will depend not only on the development of atmospheric CO2 partial pressure (pCO2), but also on changes in the catchment areas, exchange with the adjacent ocean, and internal cycling of carbon and nutrients. Here we use a coupled physical-biogeochemical Baltic Sea model to quantify the sensitivity of pH to changes both in external forcing and internal processes. The experiments include changes in runoff, supply of dissolved inorganic carbon (DIC) and total alkalinity (AT), nutrient loads, exchange between the Baltic and North Seas, and atmospheric pCO2. We furthermore address the potential different future developments of runoff and river loads in boreal and continental catchments, respectively. Changes in atmospheric pCO2 exert the strongest control on future pH according to our calculations. This CO2-induced acidification could be further enhanced in the case of desalination of the Baltic Sea, although increased concentrations of AT in the river runoff due to increased weathering to some extent could counteract acidification. Reduced nutrient loads and productivity would reduce the average annual surface water pH but at the same time slightly increase wintertime surface water pH (the annual pH minimum). The response time of surface water pH to sudden changes in atmospheric pCO2 is approximately one month, whereas response times to changes in e.g. runoff and AT/DIC loads are more related to residence times of water and salt (>30 years). It seems unlikely that the projected future increase in atmospheric pCO2 and associated pH reduction could be fully counteracted by any of the other processes addressed in our experiments.

Continue reading ‘Future acidification of the Baltic Sea – A sensitivity study’

Acidification in the U.S. Southeast: causes, potential consequences and the role of the Southeast Ocean and Coastal Acidification Network

Coastal acidification in southeastern U.S. estuaries and coastal waters is influenced by biological activity, run-off from the land, and increasing carbon dioxide in the atmosphere. Acidification can negatively impact coastal resources such as shellfish, finfish, and coral reefs, and the communities that rely on them. Organismal responses for species located in the U.S. Southeast document large negative impacts of acidification, especially in larval stages. For example, the toxicity of pesticides increases under acidified conditions and the combination of acidification and low oxygen has profoundly negative influences on genes regulating oxygen consumption. In corals, the rate of calcification decreases with acidification and processes such as wound recovery, reproduction, and recruitment are negatively impacted. Minimizing the changes in global ocean chemistry will ultimately depend on the reduction of carbon dioxide emissions, but adaptation to these changes and mitigation of the local stressors that exacerbate global acidification can be addressed locally. The evolution of our knowledge of acidification, from basic understanding of the problem to the emergence of applied research and monitoring, has been facilitated by the development of regional Coastal Acidification Networks (CANs) across the United States. This synthesis is a product of the Southeast Coastal and Ocean Acidification Network (SOCAN). SOCAN was established to better understand acidification in the coastal waters of the U.S. Southeast and to foster communication among scientists, resource managers, businesses, and governments in the region. Here we review acidification issues in the U.S. Southeast, including the regional mechanisms of acidification and their potential impacts on biological resources and coastal communities. We recommend research and monitoring priorities and discuss the role SOCAN has in advancing acidification research and mitigation of and adaptation to these changes.

Continue reading ‘Acidification in the U.S. Southeast: causes, potential consequences and the role of the Southeast Ocean and Coastal Acidification Network’

Additive impacts of deoxygenation and acidification threaten marine biota

Deoxygenation in coastal and open‐ocean ecosystems rarely exists in isolation but occurs concomitantly with acidification. Here, we first combine meta‐data of experimental assessments from across the globe to investigate the potential interactive impacts of deoxygenation and acidification on a broad range of marine taxa. We then characterize the differing degrees of deoxygenation and acidification tested in our dataset using a ratio between the partial pressure of oxygen and carbon dioxide (p O2/p CO2) to assess how biological processes change under an extensive, yet diverse range of p O2 and p CO2 conditions. The dataset comprised 375 experimental comparisons and revealed predominantly additive but variable effects (91.7%‐additive, 6.0%‐synergistic, 2.3%‐antagonistic) of the dual stressors, yielding negative impacts across almost all responses examined. Our data indicates that the p O2/p CO2‐ratio offers a simplified metric to characterize the extremity of the concurrent stressors and shows that more severe impacts occurred when ratios represented more extreme deoxygenation and acidification conditions. Importantly, our analysis highlights the need to assess the concurrent impacts of deoxygenation and acidification on marine taxa and that assessments considering the impact of O2 depletion alone will likely underestimate the impacts of deoxygenation events and their ecosystem‐wide consequences.

Continue reading ‘Additive impacts of deoxygenation and acidification threaten marine biota’

Microbial ecosystem and anthropogenic impacts

Oceans are the most vulnerable sites for anthropogenic waste from domestic as well as industrial origin. Usually, marine ecosystems are exposed to most anthropogenic stressors ranging from sewage disposal to nuclear waste contaminants. Most recent threats to marine ecosystems are ocean warming and ocean acidification (related to anthropogenic emission of CO2), oil (tarball), and (micro) plastic contamination, which is proved to have a devastating impact on the marine ecosystem. Microbes are abundantly present in marine ecosystems playing essential roles in ecosystem productivity and biogeochemistry. Generally, microbial communities are the initial responders of these stressors. Altered microbial communities in response to these stressors can, in turn, have adverse impact on the marine ecosystem and later on humans. In this review, we highlight the effect of oil pollution, microplastics, and increased CO2 on the marine microbial ecosystem. The information on the impacts of such stressors on microbial communities will be valuable to formulate appropriate remediation approaches for future use.

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Selective breeding of edible bivalves and its implication of global climate change

Bivalve molluscs are very nutritious and are an important source of human animal protein. To date, bivalve farming has contributed to about 15% of the mean per capita animal protein intake of approximate 1.5 billion people around the world. Unfortunately, the effects of climate change, mainly global warming and ocean acidification, have had many deleterious effects on bivalve aquaculture, not only leading to mass mortalities of bivalves in farms and hatcheries, but also causing collapse of natural bivalve populations. In response to the recurrent mass mortalities of farmed bivalves, many selective breeding programmes have been launched with the breeding goal of reducing mortality rate caused by disease outbreaks and changing ocean conditions. This article reviews the progress and potential of selective breeding of edible bivalves in the context of global climate change. It is clear from the literature that in terms of environmental sensitivity, and disease resistance and tolerance, selective breeding has great potential for improving the robustness of edible bivalves with significant heritability and genetic gain. Because the robustness of edible bivalves to climate change is a complex trait affected by multiple genes, the application of modern genomic tools in selective breeding is expected to dramatically enhance the accuracy and efficacy of genetic improvements and produce bivalve strains that are robust to climate change. The information in this article is very useful for guidance on adaptation strategies for climate‐smart bivalve aquaculture solutions to be implemented in bivalve hatcheries and farms.

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Ocean acidification in the IPCC AR5 WG II

OUP book