Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps

We used population reconstruction techniques to assess for the first time the population dynamics of a seagrass, Cymodocea nodosa, exposed to long-term elevated CO2 near three volcanic seeps and compare them with reference sites away from the seeps. Under high CO2, the density of shoots and of individuals (apical shoots), and the vertical and horizontal elongation and production rates, were higher. Nitrogen effects on rhizome elongation and production rates and on biomass, were stronger than CO2 as these were highest at the location where the availability of nitrogen was highest. At the seep where the availability of CO2 was highest and nitrogen lowest, density of shoots and individuals were highest, probably due to CO2 effects on shoot differentiation and induced reproductive output, respectively. In all three seeps there was higher short- and long-term recruitment and growth rates around zero, indicating that elevated CO2 increases the turnover of C. nodosa shoots.

Continue reading ‘Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps’

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’

Ocean acidification from below in the tropical Pacific

Identifying ocean acidification and its controlling mechanisms is an important priority within the broader question of understanding how sustained anthropogenic CO2 emissions are harming the health of the ocean. Through extensive analysis of observational data products for ocean inorganic carbon, here we quantify the rate at which acidification is proceeding in the western tropical Pacific Warm Pool, revealing ‐0.0013 ±0.0001 yr‐1 for pH and ‐0.0083±0.0007 yr‐1 for the saturation index of aragonite for the years 1985‐2016. However, the mean rate of total dissolved inorganic carbon increase (+0.81 ±0.06 μmol kg‐1 yr‐1) sustaining acidification was ~20% slower than what would be expected if it were simply controlled by the rate of atmospheric CO2 increase and transmitted through local air‐sea CO2 equilibration. Joint Lagrangian and Eulerian model diagnostics indicate that the acidification of the Warm Pool occurs primarily through the anthropogenic CO2 that invades the ocean in the extra‐tropics, is transported to the tropics through the thermocline shallow overturning circulation, and then re‐emerges into surface waters within the tropics through the Equatorial Undercurrent from below. An interior residence time of several years to decades, acting in conjunction with the accelerating CO2 growth in the atmosphere, can be expected to contribute to modulating the rate of Warm Pool acidification.

Continue reading ‘Ocean acidification from below in the tropical Pacific’

Late Holocene climate variability and coastal change of the Yucatan Peninsula, Mexico

The following dissertation contains three studies that use sediment cores to reconstruct past changes in the climate and environment of a tropical lagoon system. These studies provide insight into past droughts and coastal change during geologically recent climate variability and sea-level rise by investigating relationships between geochemical and biological parameters sensitive to different processes occurring on the coast of the Yucatan Peninsula, Mexico.

Chapter one is a foraminiferal fossil record reconstruction of the Celestun Lagoon environment, assessing ecologic response to a change in lagoon salinity and vegetation over the Late Holocene (5,300 years to present). The record and modern environment suggests foraminiferal community composition changes predictably with salinity, but lagoon salinity decreased primarily from restriction of seawater input to the lagoon, and hence reduced mixing between groundwater and seawater, rather than climate-induced increase of groundwater discharge, though climate is a secondary control. The cause of reduced mixing appears to be accumulation of barrier islands and sand spits that progressively isolated the northern lagoon, reducing mixing between groundwater discharge and seawater and shifting the environment from an open marine coast to estuarine lagoon. The transition was accompanied by expansion of the mangrove forest fringing the coastline. Superimposed on this trend, excursions of foraminifera taxa signify higher salinity coinciding with regionally dry periods and indicate that climate is a second-order control on lagoon mean salinity.

Chapter two is a more detailed paleosalinity reconstruction where relations between modern lagoon salinity and both trace metals and isotopes in foraminiferal tests are applied to samples from cores collected along a transect from the northern to southern lagoon. The benthic species Ammonia parkinsoniana is used due to its abundance throughout the lagoon, and paleosalinity tracers recorded in A. parkinsoniana calcite tests are the elemental ratios Sr/Ca, and Ba/Ca and isotopes δ18O and 87Sr/86Sr. Ba/Ca ratios exhibit the highest correlation with salinity while δ18O and 87Sr/86Sr indicate two types of groundwater discharge to the lagoon—a fresh and a brackish source. A mixing model constructed from δ18O and 87Sr/86Sr show that long-term decrease in salinity was due to increased proportions of the brackish groundwater endmember—consistent with the Chapter 1—and decreases in the freshwater endmember coincide with major dry periods in the Yucatan recorded in other paleoclimate archives of the region. Furthermore, sedimentation rates increase briefly at 3,400 and 2,000 years ago, time periods characterized by large-scale reorganization of atmospheric and oceanic currents in the North Atlantic with atmospheric teleconnections to tropical climate. These increases in accumulation rate are interpreted as periods of rapid barrier island accumulation as trade winds and the Loop Current weaken in the Gulf of Mexico and deposit sediments during longshore drift. Chapter two suggests that atmospheric patterns resulting in drought in the Yucatan Peninsula also result in rapid sedimentation and apparent decrease in salinity in coastal lagoons, thus demonstrating the value of a multi-proxy approach in reconstructing paleoenvironmental history in dynamic coastal environments.

Chapter three contributes data and a new hypothesis to the growing body of literature on the boron isotope system. The boron isotope ratio 11B/10B records pH of ambient water in the carbonate shells, proving to be a powerful tool in reconstructing past ocean acidification and atmospheric carbon dioxide concentrations. However, δ11B has not previously been used as a proxy for low-pH spring water discharge. In Celestun Lagoon, boron measurements in A. parkinsoniana are characterized by high variability both in surface sediments along the lagoon and in downcore samples and exhibit weak but significant relationships with the paleosalinity proxies 87Sr/86Sr and Ba/Ca and with the vegetation proxy δ13C. Lower pH caused by respiration of organic matter, recorded in δ13C of calcite, appears to contribute to δ11B variability, yet mean δ11B values of calcite reflect calculated δ11B values of borate based on present understanding of boron systematics, thus indicating that spring discharge exerts a first-order control on lagoon pH and δ11B recorded in foraminifera. This finding is of particular interest to the deep-time paleocommunity because prior to the evolution of foraminifera, and because deep sea sediments older than 180 million years are rare, many calcareous fossils available for δ11B analysis thrived in shallow marine habitats. As efforts continue to find deep-time analogs to modern ocean acidification, low-pH groundwater discharge in coastal zones may complicate interpretations of δ11B results but may be addressed by a rigorous multi-proxy approach.

This dissertation provides a record of coastal and climate change during recent periods of climate variability and sea-level rise over the last 5,000 years to provide context for current climate change in the tropics and an understanding of drivers of variability in the past and the future at low latitude sites.

Continue reading ‘Late Holocene climate variability and coastal change of the Yucatan Peninsula, Mexico’

Ocean acidification and multilateral environmental agreements

Ocean acidification is caused by increased absorption of carbon dioxide (CO2). Since the beginning of the industrial age there has been an increase of around 30 per cent in the acidity of ocean surface waters. Given that the cause is limited to CO2 emissions, there are relatively few multilateral environmental agreements (MEAs) that are relevant to the control of ocean acidification. Some, such as the Desertification Convention, are relevant in that the land-use management practices promoted under the Convention may help improve both the ability of certain areas to act as sinks and to prevent the release of CO2 as a result of poor land management. Others are more directly relevant. The United Nations Convention on the Law of the Sea (UNCLOS) addresses marine pollution from land-based sources (Article 207) and through the atmosphere (Article 212). The United Nations Framework Convention on Climate Change (UNFCCC) and the regime built upon it addresses emissions of greenhouse gases (GHGs), including CO2. Others, such as the Convention on Biological Diversity, (CBD) are relevant in that they address the impact of ocean acidification on marine species.
In this chapter we focus on three key MEAs—UNCLOS, the UNFCCC regime and the CBD—and the relationship between them. As we demonstrate, the UNFCCC and UNCLOS are, or at least should be, inextricably linked in combating ocean acidification. The CBD is focussed on impacts on marine species and has been proactive in addressing ocean acidification and bringing the need for action to the attention of the UNFCCC. The formal links between the three regimes are not, however, as strong as they ought to be to tackle ocean acidification, and so we assess the suitability of potential mechanisms to strengthen these links.

Continue reading ‘Ocean acidification and multilateral environmental agreements’

A regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry and ocean acidification in the Gulf of Alaska (update)

The coastal ecosystem of the Gulf of Alaska (GOA) is especially vulnerable to the effects of ocean acidification and climate change that can only be understood within the context of the natural variability of physical and chemical conditions. Controlled by its complex bathymetry, iron enriched freshwater discharge, and wind and solar radiation, the GOA is a highly dynamic system that exhibits large inorganic carbon variability from subseasonal to interannual timescales. This variability is poorly understood due to the lack of observations in this expansive and remote region. To improve our conceptual understanding of the system, we developed a new model set-up for the GOA that couples the three-dimensional Regional Oceanic Model System (ROMS), the Carbon, Ocean Biogeochemistry and Lower Trophic (COBALT) ecosystem model, and a high resolution terrestrial hydrological model. Here, we evaluate the model on seasonal to interannual timescales using the best available inorganic carbon observations. The model was particularly successful in reproducing observed aragonite oversaturation and undersaturation of near-bottom water in May and September, respectively. The largest deficiency of the model is perhaps its inability to adequately simulate spring time surface inorganic carbon chemistry, as it overestimates surface dissolved inorganic carbon, which translates into an underestimation of the surface aragonite saturation state at this time. We also use the model to describe the seasonal cycle and drivers of inorganic carbon parameters along the Seward Line transect in under-sampled months. As such, model output suggests that a majority of the near-bottom water along the Seward Line is seasonally under-saturated with regard to aragonite between June and January, as a result of upwelling and remineralization. Such an extensive period of reoccurring aragonite undersaturation may be harmful to CO2 sensitive organisms. Furthermore, the influence of freshwater not only decreases aragonite saturation state in coastal surface waters in summer and fall, but simultaneously also decreases surface pCO2, thereby decoupling the aragonite saturation state from pCO2. The full seasonal cycle and geographic extent of the GOA region is undersampled, and our model results give new and important insights for months of the year and areas that lack in situ inorganic carbon observations.

Continue reading ‘A regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry and ocean acidification in the Gulf of Alaska (update)’

The characteristics of the CO2 system of the Oder River estuary (Baltic Sea)

Highlights

• The CO2 system in the Oder River Estuary was investigated for the first time.

• OM production and remineralization affect the CO2 system in the Oder River Estuary.

• Extreme primary production may initiate mineral precipitation of calcite in high AT.

• Estuarine processes may modify the riverine loads of AT and CT to the Baltic Sea.

Abstract

This study examined the CO2 system in the estuary of the Oder River, one of the largest rivers entering the Baltic Sea. Three measurable parameters describing the CO2 system, namely total alkalinity (AT), total CO2 (CT), and the partial pressure of CO2 (pCO2), were investigated together with dissolved oxygen, salinity (S), and temperature during two RV Oceania cruises, in May and November of 2016. Large spatial variabilities of AT (1771–2940 μmol kg−1) and CT (1676–2972 μmol kg−1) were determined along the S gradient between the open Baltic Sea and river mouth. In November, the relationships of AT–S and CT-S indicated conservative mixing whereas in May both were strongly affected by biomass production and calcium carbonate formation. The waters of the Oder were oversaturated with CO2 compared to the atmosphere, irrespective of the season, with pCO2 values of 1351 ± 42 μatm in May and 1120 ± 32 μatm in November. In the Szczecin Lagoon, however, pCO2 levels dropped significantly, to 63 μatm, in May, accompanied by an O2 saturation of up to 134% during the same period. The inverse correlation of pCO2 and O2 saturation indicated that the distribution of CO2 and O2 in the estuary at the time of sampling was controlled mostly by biological activity. The very large drop in the pCO2 of the Szczecin Lagoon induced an extreme oversaturation of CaCO3 that triggered mineral calcite precipitation. The mineral precipitation of carbonates in the lagoon may have accounted for as much as 40% of the CT depletion determined in May, with the remaining 60% attributed to the joint effect of net ecosystem production and CO2 air/water gas exchange.

Continue reading ‘The characteristics of the CO2 system of the Oder River estuary (Baltic Sea)’

Fragmented kelp forest canopies retain their ability to alter local seawater chemistry

Kelp forests support some of the most productive and diverse ecosystems on Earth, and their ability to uptake dissolved inorganic carbon (DIC) allows them to modify local seawater chemistry, creating gradients in carbon, pH, and oxygen in their vicinity. By taking up both bicarbonate and CO2 as a carbon source for photosynthesis, kelp forests can act as carbon sinks, reducing nearby acidity and increasing dissolved oxygen; creating conditions conducive to calcification. Recent stressors, however, have reduced kelp forest canopies globally; converting once large and persistent forests to fragmented landscapes of small kelp patches. In a two-year study, we determined whether fragmented kelp patches retained the ability to alter local seawater chemistry. We found that diel fluctuations of multiple parameters of carbonate chemistry were greater in the kelp canopy than in the kelp benthos and in adjacent urchin barrens, consistent with metabolic activity by the kelp. Further, kelp fragments increased pH and aragonite saturation and decreased pCO2 during the day to a similar degree as large, intact kelp forests. We conclude that small kelp patches could mitigate OA stress and serve as spatial and temporal refugia for canopy-dwelling organisms, though this effect is temporary and confined to daylight hours during the growing season.

Continue reading ‘Fragmented kelp forest canopies retain their ability to alter local seawater chemistry’

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’

Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalga Pyropia haitanensis (Bangiales, Rhodophyta)

The present research investigated the effect of pCO2 levels (C), seawater temperature (T), and nutrient availability (N) on the growth and physiochemical changes in Pyropia haitanensis. With nutrient enrichment, the interaction of higher pCO2 increased relative growth rates (RGR) by 105.9% when temperature increased (22 °C) compared with the control (lower T, lower C, and lower N: LTLCLN). The higher pCO2 decreased the Pm rates at the lower temperature (18 °C), yet displayed no interaction with higher T or N levels. The higher N increased dark respiration rate (Rd) at 18 °C. At 22 °C, higher pCO2 significantly enhanced the maximum ratio of (quantum yields (Fv/Fo) and the maximum quantum yield (ψpo), while it sharply decreased the absorption of photons per active reaction center (ABS/RC) and dissipation of energy fluxes (per RC) (DIo/RC). Higher temperature obviously reduced the Fv/Fo and ψpo under ambient CO2 level. The higher pCO2 significantly increased the phycoerythrin (PE) and phycocyanin (PC) contents, while higher temperature decreased the PE contents with elevated CO2 and declined the PC content regardless of CO2 condition. At lower nutrient condition, higher pCO2 increased Chl a content. Soluble carbohydrates (SC) and soluble protein (SP) content almost was unchanged among all treatments. Our findings indicate that nutrient availability may regulate photosynthetic mechanism to offset the negative effect of future ocean warming on P. haitanensis, thereby sustaining or increasing the biomass yield of the algae.

Continue reading ‘Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalga Pyropia haitanensis (Bangiales, Rhodophyta)’


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Ocean acidification in the IPCC AR5 WG II

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