Posts Tagged 'phanerogams'

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’

Interaction of short-term copper pollution and ocean acidification in seagrass ecosystems: toxicity, bioconcentration and dietary transfer

Highlights

• Toxicity and bioconcentration of copper in seagrasses were not affected by pH.
• Complex copper-pH interactions were observed in the seagrass photosynthesis.
• Seagrasses can act as a copper source in the food web via direct consumption.

Abstract

We aimed to show how the predicted pH decrease in the ocean would alter the toxicity, bioconcentration and dietary transfer of trace metal copper on seagrass ecosystems, on a short-term basis. Seagrass Zostera noltei was exposed to two pH levels (8.36 and 8.03) and three copper levels (nominal concentrations, <3, 30 and 300 μg Cu L−1) in a factorial design during 21 days, while Gammarus locusta amphipods were continuously fed with the treated seagrass leaves. We found that the toxicity and bioconcentration of copper in seagrasses were not affected by pH, yet complex copper-pH interactions were observed in the seagrass photosynthesis. We demostrated that seagrasses can act as a copper source in the food web via direct consumption by herbivores. Future research need to investigate the interactive effects on a long-term basis, and to include biochemical and molecular endpoints to provide additional insights to the complex phisiological interactions observed.

Continue reading ‘Interaction of short-term copper pollution and ocean acidification in seagrass ecosystems: toxicity, bioconcentration and dietary transfer’

Studentized bootstrap model-averaged tail area intervals

In many scientific studies, the underlying data-generating process is unknown and multiple statistical models are considered to describe it. For example, in a factorial experiment we might consider models involving just main effects, as well as those that include interactions. Model-averaging is a commonly-used statistical technique to allow for model uncertainty in parameter estimation. In the frequentist setting, the model-averaged estimate of a parameter is a weighted mean of the estimates from the individual models, with the weights typically being based on an information criterion, cross-validation, or bootstrapping. One approach to building a model-averaged confidence interval is to use a Wald interval, based on the model-averaged estimate and its standard error. This has been the default method in many application areas, particularly those in the life sciences. The MA-Wald interval, however, assumes that the studentized model-averaged estimate has a normal distribution, which can be far from true in practice due to the random, data-driven model weights. Recently, the model-averaged tail area Wald interval (MATA-Wald) has been proposed as an alternative to the MA-Wald interval, which only assumes that the studentized estimate from each model has a N(0, 1) or t-distribution, when that model is true. This alternative to the MA-Wald interval has been shown to have better coverage in simulation studies. However, when we have a response variable that is skewed, even these relaxed assumptions may not be valid, and use of these intervals might therefore result in poor coverage. We propose a new interval (MATA-SBoot) which uses a parametric bootstrap approach to estimate the distribution of the studentized estimate for each model, when that model is true. This method only requires that the studentized estimate from each model is approximately pivotal, an assumption that will often be true in practice, even for skewed data. We illustrate use of this new interval in the analysis of a three-factor marine global change experiment in which the response variable is assumed to have a lognormal distribution. We also perform a simulation study, based on the example, to compare the lower and upper error rates of this interval with those for existing methods. The results suggest that the MATA-SBoot interval can provide better error rates than existing intervals when we have skewed data, particularly for the upper error rate when the sample size is small.

Continue reading ‘Studentized bootstrap model-averaged tail area intervals’

Habitat effects of macrophytes and shell on carbonate chemistry and juvenile clam recruitment, survival, and growth

Highlights

• Field experiment testing two substrate treatments as OA adaptation strategies
• Clam growth increased in absence of macrophytes, regardless of shell hash treatment.
• Neither treatment improved clam recruitment or survival.
• pH in water column was higher during the day and outside eelgrass beds.
• Added shell hash improved carbonate chemistry in sediment pore-water.

Abstract

Adverse habitat conditions associated with reduced seawater pH often, but not always, negatively affect bivalves in early life history phases. Improving our understanding of how habitat-specific parameters affect clam recruitment, survival, and growth could assist natural resource managers and researchers in developing appropriate adaptation strategies for increasingly acidified nearshore ecosystems. Two proposed adaptation strategies, the presence of macrophytes and addition of shell hash, have the potential to raise local seawater pH and aragonite saturation state and, therefore, to improve conditions for shell-forming organisms. This field study examined the effects of these two substrate treatments on biological and geochemical response variables. Specifically, we measured (1) recruitment, survival, and growth of juvenile clams (Ruditapes philippinarum) and (2) local water chemistry at Fidalgo Bay and Skokomish Delta, Washington, USA, in response to experimental manipulations. Results showed no effect of macrophyte or shell hash treatment on recruitment or survival of R. philippinarum. Contrary to expectations, clam growth was significantly greater in the absence of macrophytes, regardless of the presence or absence of shell hash. Water column pH was higher outside the macrophyte bed than inside at Skokomish Delta and higher during the day than at night at Fidalgo Bay. Additionally, pore-water pH and aragonite saturation state were higher in the absence of macrophytes and the presence of shell. Based on these results, we propose that with increasingly corrosive conditions shell hash may help provide chemical refugia under future ocean conditions. Thus, we suggest adaptation strategies target the use of shell hash and avoidance of macrophytes to improve carbonate chemistry conditions and promote clam recruitment, survival, and growth.

Continue reading ‘Habitat effects of macrophytes and shell on carbonate chemistry and juvenile clam recruitment, survival, and growth’

Expected limits on the ocean acidification buffering potential of a temperate seagrass meadow

Ocean acidification threatens many marine organisms, especially marine calcifiers. The only global‐scale solution to ocean acidification remains rapid reduction in CO2 emissions. Nevertheless, interest in localized mitigation strategies has grown rapidly because of the recognized threat ocean acidification imposes on natural communities, including ones important to humans. Protection of seagrass meadows has been considered as a possible approach for localized mitigation of ocean acidification due to their large standing stocks of organic carbon and high productivity. Yet much work remains to constrain the magnitudes and timescales of potential buffering effects from seagrasses. We developed a biogeochemical box model to better understand the potential for a temperate seagrass meadow to locally mitigate the effects of ocean acidification. Then we parameterized the model using data from Tomales Bay, an inlet on the coast of California, USA which supports a major oyster farming industry. We conducted a series of month‐long model simulations to characterize processes that occur during summer and winter. We found that average pH in the seagrass meadows was typically within 0.04 units of the pH of the primary source waters into the meadow, although we did find occasional periods (hours) when seagrass metabolism may modify the pH by up to ±0.2 units. Tidal phasing relative to the diel cycle modulates localized pH buffering within the seagrass meadow such that maximum buffering occurs during periods of the year with midday low tides. Our model results suggest that seagrass metabolism in Tomales Bay would not provide long‐term ocean acidification mitigation. However, we emphasize that our model results may not hold in meadows where assumptions about depth‐averaged net production and seawater residence time within the seagrass meadow differ from our model assumptions. Our modeling approach provides a framework that is easily adaptable to other seagrass meadows in order to evaluate the extent of their individual buffering capacities. Regardless of their ability to buffer ocean acidification, seagrass meadows maintain many critically important ecosystem goods and services that will be increasingly important as humans increasingly affect coastal ecosystems.

Continue reading ‘Expected limits on the ocean acidification buffering potential of a temperate seagrass meadow’

Global warming and ocean acidification: effects on Australian seagrass ecosystems

As concentrations of atmospheric CO2 increase, mean temperatures across the globe rise, the carbon system equilibrium in the ocean shifts, and pH is reduced in a process termed Ocean Acidification (OA). These changes can dramatically alter seagrass meadows as both temperature and pH fundamentally influence biochemistry and physiology of plants. Seagrass responses to climate change are species-specific and dependent on interactions with other factors such as light intensity, nutrient availability and competition. The majority of seagrasses appear limited by the availability of dissolved inorganic carbon at current ocean pH, suggesting that rates of photosynthesis and growth are likely to increase with OA. Short- and intermediate term laboratory experiments have shown an increase in photosynthetic rates to increased pCO2. Longer-term studies (>1 year) indicate enhanced shoot proliferation resulting in meadows with high shoot density. Studies utilizing natural gradients in pCO2 that exist near shallow volcanic CO2 vents have shown that, overall, seagrasses appear to benefit from OA. Seagrasses photosynthesize across a range in temperatures, but rapidly decline above thermal optima. Respiration rates increase with warming at a faster rate than photosynthesis and reduces the overall photosynthesis-to-respiration ratio, and thus growth. While seagrasses can recover from moderate temperature stress, extreme temperatures result in mortality. Future changes in seagrass species distributions are predicted as sensitive species shift poleward. Foundation species, like seagrasses, have a large influence on their environment and their loss can significantly impact the functioning of the whole ecosystem. Despite a recent increase in climate-change research, we lack an understanding of how seagrass meadows are going to respond to the combined pressures of warming and OA. It is particularly difficult to predict longer-term responses and possible adaptation, and efforts should be focused in this area to determine how we can manage seagrasses to maximize resilience to climate change.

Continue reading ‘Global warming and ocean acidification: effects on Australian seagrass ecosystems’

The ability of Phyllospadix spp., a pair of intertidal foundation species, to maintain biodiversity and ameliorate CO2 stress in rocky shore tidepools

Ocean acidification (OA) is often demonstrated to have negative effects on marine organisms, but less is known about whether marine organisms can mediate OA effects. I examined relationships between surfgrass (Phyllospadix spp.), a foundation species and tidepool biodiversity, and its ability to mediate fluctuations in pH and dissolved oxygen (OA; DO) which are stressors in tidepools. I surveyed tidepools in northern California, where I quantified biodiversity, pH, and DO, and related those variables to surfgrass abundance. Laboratory and field experiments manipulating CO2 and surfgrass presence were done to examine surfgrass effects on day/night pH and DO fluctuations in simulated and natural tidepools. Intermediate surfgrass abundance was associated with the greatest tidepool biodiversity in the field, suggesting amelioration of abiotic conditions up to intermediate abundances, but exacerbated OA and DO stress at higher abundances. In the lab, diel pH and DO fluctuations were highest in simulated tidepools that contained surfgrass compared to pools without surfgrass, indicating the role of surfgrass photosynthesis and respiration in modulating seawater chemistry. In the field, tidepool pH and DO were higher in the day and lower at night, consistent with results from the laboratory experiment. Interestingly, day/night fluctuations in pH were highest in tidepools with intermediate rather than high surfgrass abundance, suggesting the intriguing possibility that surfgrass modulates tidepool pH both directly via metabolic activity but also indirectly by facilitating macrophyte diversity at intermediate abundances. Taken together, these results suggest that surfgrass may act as a foundation species in tidepools, by mediating tidepool pH and influencing species diversity, which has important implications for the fate of these communities in the face of rapidly-changing global climates.

Continue reading ‘The ability of Phyllospadix spp., a pair of intertidal foundation species, to maintain biodiversity and ameliorate CO2 stress in rocky shore tidepools’


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Ocean acidification in the IPCC AR5 WG II

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