Posts Tagged 'morphology'

Transgenerational effects decrease larval resilience to ocean acidification & warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic

The aim of this study was to investigate the effect of ocean acidification (OA) and warming (OW) as well as the transgenerational effect of OA on larval and juvenile growth and metabolism of a large economically important fish species with a long generation time. Therefore we incubated European sea bass from Brittany (France) for two generations (>5 years in total) under current and predicted OA conditions (PCO2: 650 and 1700 µatm). In the F1 generation both OA condition were crossed with OW (temperature: 15-18°C and 20-23°C). We found that OA alone did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine metabolic rate (RMR) and juvenile standard metabolic rate (SMR) were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA on RMR or SMR. Juvenile PO2crit was not affected by OA, OW or OAW in both generations.

We discuss the potential underlying mechanisms resulting in beneficial effects of OW on F1 larval growth and RMR and in resilience of F0 and F1 larvae and juveniles to OA, but on the other hand resulting in vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

Summary statement We found that OA did not affect developmental time, growth, RMR and SMR, while OW increased these traits. OAW decreased larval size at metamorphosis. We discuss underlying mechanisms and the ecological perspective resulting from these results and conclude that recruitment to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures in Atlantic waters.

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Effects of ocean acidification on the biochemistry, physiology and parental transfer of Ampelisca brevicornis (Costa, 1853)

Highlights

  • Acidification had a deleterious impact on physiological and biochemical responses.
  • Ampelisca altered the age and size of reproductive maturity.
  • Antioxidant mechanisms were overcome in predicted acidified conditions.
  • The impact on growth had serious consequences on reproductive performance.
  • Survival was high in generation F1 than F0 juveniles and vice-versa in growth.

Abstract

Ocean acidification (OA) has gotten more attention in the marine research community in recent years than any other topic. Excess carbon dioxide makes the ocean more acidic, threatening marine ecosystems. There has been little research on the impact of OA on crustaceans, particularly on their physiological and potential ecosystem-level consequences. Thus, we investigated the impacts of OA on the physiological and biochemical characteristics of the estuarine amphipod A. brevicornis. Ovigerous amphipods were harvested from nature and maintained in the laboratory to produce juveniles; which were then further reared to obtain the mature adults (F0) and successive offspring (F1). For this study, four pH treatments (pH 8.1, 7.5, 7.0 and 6.5) mimicking future OA were evaluated to understand the physiological and biochemical effects on the organisms. The findings of this study suggest that A. brevicornis is more vulnerable to OA than was previously established in short-term trials. The survival was significantly reduced as pH decreased over time and a significant interaction between pH and time was observed. Survival was higher in F1 than F0 juveniles and vice-versa in terms of growth. Animal’s physiological responses such as growth, burrowing behaviors, locomotor activity, swimming speed, ventilation rate, and reproductive performances were all negatively influenced by acidification. These physiological characteristics can be linked to the oxidative stress induced by global change conditions because excess free radicals degrade cell functioning, affecting species’ biochemical and physiological performance. These alterations may not only have long-term negative consequences, but they may also have ecological consequences. The results of this study provide baseline information regarding effect of OA on this keystone crustacean that may be useful in simulating the impacts of OA to develop different conceptual models for a better understanding of climate change’s consequences and implications in the future for managing marine ecosystem.

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Ocean acidification reduces the growth of two Southern Ocean phytoplankton

Model projections for the Southern Ocean indicate that light, iron (Fe) availability, temperature and carbon dioxide (CO2) will change concurrently in the future. We investigated the physiological responses of Southern Ocean phytoplankton to multiple variables by culturing the haptophyte Phaeocystis antarctica and the diatom Chaetoceros flexuosus under various combinations of light, Fe, temperature and CO2. Using statistical models, the influence of each environmental variable was analysed for each physiological response, ultimately predicting how ‘future’ conditions (high temperature and high CO2) influenced the two phytoplankton species. Under future conditions, cellular chlorophyll a and carbon to nitrogen molar ratios were modelled to increase for both species, in all light and Fe treatments, but at times were inconsistent with measured values. Measured and modelled values of the photochemical efficiency of photosystem II (Fv/Fm) declined in cultures of P. antarctica due to concurrent increases in temperature and CO2, under all light and Fe treatments. The trends in Fv/Fm for C. flexuosus were less clear. Our model and observations suggest that when temperature and CO2 are concurrently increased, the growth of both species remains largely unchanged. This modelling analysis reveals that high CO2 exerts a strong negative influence on the growth of both phytoplankton, and any ‘future’ increase in growth can be attributed to the positive effect of warming rather than a CO2 fertilisation effect.

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Experimentally decomposing phytoplankton community change into ecological and evolutionary contributions

  1. Shifts in microbial communities and their functioning in response to environmental change result from contemporary interspecific and intraspecific diversity changes. Interspecific changes are driven by ecological shifts in species composition, while intraspecific changes are here assumed to be dominated by evolutionary shifts in genotype frequency. Quantifying the relative contributions of interspecific and intraspecific diversity shifts to community change thus addresses the essential, yet understudied question as to how important ecological and evolutionary contributions are to total community changes. This debate is to date practically constrained by (a) a lack of studies integrating across organizational levels and (b) a mismatch between data requirements of existing partitioning metrics and the feasibility to collect such data, especially in microscopic organisms like phytoplankton.
  2. We experimentally assessed the relative ecological and evolutionary contributions to total phytoplankton community changes using a new design and validated its functionality by comparisons to established partitioning metrics. We used a community of coexisting Emiliania huxleyi and Chaetoceros affinis with initially nine genotypes each. First, we exposed the community to elevated CO2 concentration for 80 days (~50 generations) to induce interspecific and intraspecific diversity changes and a total abundance change. Second, we independently manipulated the induced interspecific and intraspecific diversity changes in an assay to quantify the corresponding ecological and evolutionary contributions to the total change. Third, we applied existing partitioning metrics to our experimental data and compared the outcomes.
  3. Total phytoplankton abundance declined to one-fifth in the high CO2 exposed community compared to ambient conditions. Consistently across all applied partitioning metrics, the abundance decline could predominantly be explained by ecological shifts and to a low extent by evolutionary changes.
  4. We discuss potential consequences of the observed community changes on ecosystem functioning. Furthermore, we explain that the low evolutionary contributions likely resulted of intraspecific diversity changes that occurred irrespectively of CO2. We discuss how the assay could be upscaled to more realistic settings, including more species and drivers. Overall, the presented calculations of eco-evolutionary contributions to phytoplankton community changes constitute another important step towards understanding future phytoplankton shifts, and eco-evolutionary dynamics in general.
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Near-future levels of pCO2 impact skeletal weights of coral primary polyps (Acropora digitifera)

Ocean acidification poses a severe threat to corals; declines in carbonate ion concentrations caused by increasing atmospheric CO2 partial pressure (pCO2) can severely impact coral calcification. Thus, there is an urgent need to understand the impacts of near-future ocean acidification on corals. In this study, we compared the effects of seawater at present and near-future pCO2 (approximately +200 μatm) levels on skeletal weights of new coral recruits. Experiments were carried out using precisely pCO2-controlled aquaria supplying stable pCO2-controlled seawater in a flow-through system. Our results show that skeletal weights of new coral recruits decreased significantly at +200 μatm pCO2, which is expected to be reached within this century if ocean acidification continues at the present pace.

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Climate change alters shellfish reef communities: a temperate mesocosm experiment

Highlights

  • Climate change will cause significant changes to rocky shore diversity.
  • Outdoor mesocosms were used to test predictions of warming and ocean acidification.
  • Elevated carbon dioxide in the atmosphere reduced the growth of the native mussels.
  • Warming and carbon dioxide influenced the species that colonised the mussels.

Abstract

Climate change is expected to cause significant changes to rocky shore diversity. This study used outdoor mesocosms to test the predictions that warming and ocean acidification will alter the responses of native Trichomya hirsuta and introduced Mytilus galloprovincialis mussels, and their associated communities of infauna. Experiments consisted of orthogonal combinations of temperature (ambient 22 °C or elevated 25 °C), pCO2 (ambient 400 μatm or elevated 1000 μatm), mussel species (T. hirsuta or M. galloprovincialis), and mussel configuration (native, introduced, or both), with n = 3 replicates. Elevated pCO2 reduced the growth of T. hirsuta but not that of M. galloprovincialis, and warming and pCO2 influenced the infauna that colonised both species of mussels. There was a reduction in infaunal molluscs and an increase in polychaetes; there was, however, no effect on crustaceans. Results from this study suggest that climate-driven changes from one mussel species to another can significantly influence infaunal communities.

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Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems

Highlights

  • Ocean acidification (OA) and ocean cooling (OC) will influence upwelling systems.
  • The snail Acanthina monodon growth, feeding and calcification rates increased with OC.
  • Metabolic rates also increased with OA but only under OC conditions.
  • Self-righting was unaltered, suggesting a complex repertoire of responses to OA and OC.

Abstract

Ocean acidification (OA) is expected to rise towards the end of the 21st century altering the life history traits in marine organisms. Upwelling systems will not escape OA, but unlike other areas of the ocean, cooling effects are expected to intensify in these systems. Regardless, studies evaluating the combined effects of OA and cooling remain scarce. We addressed this gap using a mesocosm system, where we exposed juveniles of the intertidal muricid snail Acanthina monodon to current and projected pCO2 (500 vs. 1500 ppm) and temperature (15 vs. 10 °C) from the southeast Pacific upwelling system. After 9 weeks of experimental exposure to those conditions, we conducted three estimations of growth (wet weight, shell length and shell peristomal length), in addition to measuring calcification, metabolic and feeding rates and the ability of these organisms to return to the normal upright position after being overturned (self-righting). Growth, feeding and calcification rates increased in projected cooling conditions (10 °C) but were unaffected by pCO2 or the interaction between pCO2 and temperature. Instead, metabolic rates were driven by pCO2, but a significant interaction with temperature suggests that in cooler conditions, metabolic rates will increase when associated with high pCO2 levels. Snail self-righting times were not affected across treatments. These results suggest that colder temperatures projected for this area would drive this species growth, feeding and calcification, and consequently, some of its population biology and productivity. However, the snails may need to compensate for the increase in metabolic rates under the effects of ocean acidification. Although A. monodon ability to adjust to individual or combined stressors will likely account for some of the changes described here, our results point to a complex dynamic to take place in intertidal habitats associated with upwelling systems.

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Experimental studies on the impact of the projected ocean acidification on fish survival, health, growth, and meat quality; Black Sea bream (Acanthopagrus schlegelii), physiological and histological studies

Simple Summary

This study’s data suggest that under the projected scenarios of ocean acidification by 2100 and beyond, significant negative impacts on growth, health, and meat quality are expected, particularly on black sea bream, and will be susceptible to the scientifically approved fish having a weaker resistance to diseases and environmental changes if CO2 emissions in the atmosphere are not curbed. Knowing the expected consequences, mitigation measures are urgently needed.

Abstract

Acidification (OA), a global threat to the world’s oceans, is projected to significantly grow if CO2 continues to be emitted into the atmosphere at high levels. This will result in a slight decrease in pH. Since the latter is a logarithmic scale of acidity, the higher acidic seawater is expected to have a tremendous impact on marine living resources in the long-term. An 8-week laboratory experiment was designed to assess the impact of the projected pH in 2100 and beyond on fish survival, health, growth, and fish meat quality. Two projected scenarios were simulated with the control treatment, in triplicates. The control treatment had a pH of 8.10, corresponding to a pCO2 of 321.37 ± 11.48 µatm. The two projected scenarios, named Predict_A and Predict_B, had pH values of 7.80-pCO2 = 749.12 ± 27.03 and 7.40-pCO2 = 321.37 ± 11.48 µatm, respectively. The experiment was preceded by 2 weeks of acclimation. After the acclimation, 20 juvenile black sea breams (Acanthopagrus schlegelii) of 2.72 ± 0.01 g were used per tank. This species has been selected mainly due to its very high resistance to diseases and environmental changes, assuming that a weaker fish resistance will also be susceptibly affected. In all tanks, the fish were fed with the same commercial diet. The seawater’s physicochemical parameters were measured daily. Fish samples were subjected to physiological, histological, and biochemical analyses. Fish growth, feeding efficiency, protein efficiency ratio, and crude protein content were significantly decreased with a lower pH. Scanning electron microscopy revealed multiple atrophies of microvilli throughout the small intestine’s brush border in samples from Predict_A and Predict_B. This significantly reduced nutrient absorption, resulting in significantly lower feed efficiency, lower fish growth, and lower meat quality. As a result of an elevated pCO2 in seawater, the fish eat more than normal but grow less than normal. Liver observation showed blood congestion, hemorrhage, necrosis, vacuolation of hepatocytes, and an increased number of Kupffer cells, which characterize liver damage. Transmission electron microscopy revealed an elongated and angular shape of the mitochondrion in the liver cell, with an abundance of peroxisomes, symptomatic of metabolic acidosis.

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Physiological response of shellfish native to the North American Pacific Coast to ocean acidification and warming

Following observations of shifting ocean conditions an enormous scientific effort has explored the response of marine species to ocean acidification and warming. Empirical data has established that many species are vulnerable to ocean conditions projected for this century, particularly calcifying invertebrates, affecting a range of physiological processes over the lifetime of an organism. However, these studies also indicate that biological responses are quite variable, related to an organism’s genetic and environmental ancestries. Some species are more tolerant to the effects of acidification than others, as are some populations within species. There is also evidence that transgenerational carryover effects may alleviate some negative effects by buffering future generations against challenging conditions. The future of marine ecosystems and food systems hinges in part upon our ability to identify, conserve, and invest in individuals that can tolerate shifting ocean conditions, and to understand the role of transgenerational carryover effects in shaping future populations.

The aim of this dissertation work is to examine the physiological and molecular responses of two invertebrate species native to the North American Pacific Coast, the Olympia oyster (Ostrea lurida) and Pacific geoduck (Panopea generosa), to ocean acidification and warming. Both species inhabit dynamic, heterogeneous estuarine environments that are influenced by coastal upwelling, and through adaptation and/or carryover effects may be relatively tolerant of ocean change. By testing multiple species, populations, life stages, and generations I provide evidence that these Pacific Coast natives are uniquely equipped for the effects of ocean acidification, and that warming will be a more impactful, but not necessarily negative, driver of physiological changes.

Chapter 1 characterizes the proteomes of Pacific geoduck in varying natural environments and habitat-specific pH conditions. Juvenile geoduck were deployed in eelgrass and adjacent unvegetated habitats for 30 days while pH, temperature, dissolved oxygen, and salinity were monitored. Across the four deployment locations pH was lower in unvegetated habitats compared to eelgrass habitats. While geoduck growth and proteomes were not affected by pH, they were sensitive to temperature and dissolved oxygen, but neither affected survival rates. Chapter 1 demonstrates that geoduck may be resilient to acidification in a natural setting and temperature may have a greater influence on geoduck physiology.

Chapter 2 examines the intra- and inter-generational carryover effects of ocean warming in the Olympia oyster. In many species reproductive and metabolic processes are tightly linked to the seasonal change from winter to spring, yet we know little about how these processes will shift as winters become milder. Therefore, in Chapter 2 I exposed adult Olympia oysters to elevated winter temperature and monitored effects to reproduction and offspring viability in spring. Parental exposure to warming did not affect overall larval production or survival, however it did increase the size and development of gametes, and the size of larval offspring. In the wild more developed gametes and larger larvae following milder winters could greatly impact recruitment patterns, possibly benefitting O. lurida populations. The results of Chapter 2 suggest that O. lurida is at minimum resilient to winter warming, and at best could benefit from it due to improved larval viability.

Chapter 3 continues exploring carryover effects in the Olympia oyster by examining the effects of combined ocean warming and acidification across three distinct O. lurida populations. Larval production was higher and began sooner following winter warming, was reduced by acidification, but was unaffected by combined stressors. Offspring of parents exposed to acidification, which were reared in common conditions for one year, had higher survival rates when tested in the field. Results of Chapter 3 indicate that altered recruitment patterns may follow warmer winters due to a prolonged reproductive season and/or increased production, but these effects may be masked by coincidental high pCO2. Furthermore, Olympia oysters may be more resilient in certain environments when progenitors are pre-conditioned in stressful conditions. This carryover effect demonstrates that parental conditions can have substantial ecologically relevant impacts that should be considered when predicting impacts of environmental change.

Chapter 4 further describes three O. lurida populations’ responses to acidification by examining growth, reproductive development, gene expression, and signals in offspring. Responses reveal energetic trade-offs that range from a robust transcriptional response in one population (Dabob Bay) without impacts to growth or reproduction, to no detectable transcriptional response but negative impacts to growth and reproduction in another (Oyster Bay). While exposure to acidification did not affect gene expression in the next generation’s larval stage, it did increase larval size in the Oyster Bay, which could partially alleviate negative effects of acidification in the wild in that population. Given the distinct transcriptional response of the Dabob Bay population to acidification and its high survival rates in previous studies, we identified genes unique to that population, which provide insight into the mechanisms behind a stress-tolerant oyster population. Chapter 4 provides the first description of molecular processes responsive to acidification in an Ostrea spp, and demonstrates that species inhabiting heterogeneous environments, even on small geographic scales, offer natural reservoirs of biodiversity.

This dissertation work reveals the resilience of bivalves native to the Northeast Pacific Ocean to ocean change, and suggests that that Olympia oyster and Pacific geoduck are good candidates for aquaculture investment and conservation efforts. Furthermore, population-specific responses and carryover effects observed in Olympia oyster suggests that both fine-scale genetic structure and parental priming can influence how an organism responds to ocean change, and should be considered by conservationists and managers, and in future studies.

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Pulsed pressure: fluctuating impacts of multifactorial environmental change on a temperate macroalgal community

Global change impacts marine organisms and communities mainly through ocean warming, acidification, deoxygenation, and changes in nutrient inputs and water circulation. To assess the ecological impacts of global change, the effects of multiple interacting environmental drivers, including their fluctuations, should be tested at different levels of biological organization. In an outdoor mesocosm study, we investigated the differential effects of three simulated upwelling events coupled with ocean warming (1–5°C above ambient) on a temperate benthic community in the Western Baltic Sea. Ocean warming, especially in summer when temperatures are close to or above the physiological optimum of many species, is likely to impose thermal stress with species-specific impacts. As the properties of deep water vary seasonally, so will the effects of upwelling. Upwelling of cooler deep water in midsummer may alleviate thermal stress, although this mitigation may be modulated by upwelling-associated shifts in other water-quality parameters such as salinity, nutrients, or late-summer hypoxia. This investigation showed that in the Western Baltic Ocean warming was rather beneficial in early and late summer but detrimental when ambient temperatures were highest in midsummer. The effects of upwelling in the absence of ocean warming were generally weakly beneficial, while this effect tended to vanish with intensifying imposed ocean warming. Hypoxia associated with the late summer upwelling impacted some of the grazer species but did not impact the macroalgae. We conclude that in coastal temperate benthic communities, ocean warming is the predominant stressor that may partially and seasonally be buffered by upwelling.

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The effects of low pH on the taste and amino acid composition of tiger shrimp

Recent research has revealed that shrimp sensory quality may be affected by ocean acidification but we do not exactly know why. Here we conducted controlled pH exposure experiments on adult tiger shrimp, which were kept in 1000-L tanks continuously supplied with coastal seawater. We compared survival rate, carapace properties and flesh sensory properties and amino acid composition of shrimp exposed to pH 7.5 and pH 8.0 treatments for 28 days. Shrimp reared at pH 7.5 had a lower amino acid content (17.6% w/w) than those reared at pH 8.0 (19.5% w/w). Interestingly, the amino acids responsible for the umami taste, i.e. glutamate and aspartic acid, were present at significantly lower levels in the pH 7.5 than the pH 8.0 shrimp, and the pH 7.5 shrimp were also rated as less desirable in a blind quality test by 40 volunteer assessors. These results indicate that tiger shrimp may become less palatable in the future due to a lower production of some amino acids. Finally, tiger shrimp also had a lower survival rate over 28 days at pH 7.5 than at pH 8.0 (73% vs. 81%) suggesting that ocean acidification may affect both the quality and quantity of future shrimp resources.

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Synthesis of thresholds of ocean acidification impacts on decapods

Assessing decapod sensitivity to regional-scale ocean acidification (OA) conditions is limited because of a fragmented understanding of the thresholds at which they exhibit biological response. To address this need, we undertook a three-step data synthesis: first, we compiled a dataset composed of 27,000 datapoints from 55 studies of decapod responses to OA. Second, we used statistical threshold analyses to identify OA thresholds using pH as a proxy for 13 response pathways from physiology to behavior, growth, development and survival. Third, we worked with the panel of experts to review these thresholds, considering the contributing datasets based on quality of the study, and assign a final thresholds and associated confidence scores based on quality and consistency of findings among studies. The duration-dependent thresholds were within a pH range from 7.40 to 7.80, ranging from behavioral and physiological responses to mortality, with many of the thresholds being assigned medium-to-high confidence. Organism sensitivity increased with the duration of exposure but was not linked to a specific life-stage. The thresholds that emerge from our analyses provide the foundation for consistent interpretation of OA monitoring data or numerical ocean model simulations to support climate change marine vulnerability assessments and evaluation of ocean management strategies.

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Rapid enhancement of multiple ecosystem services following the restoration of a coastal foundation species

The global decline of marine foundation species (kelp forests, mangroves, salt marshes, and seagrasses) has contributed to the degradation of the coastal zone and threatens the loss of critical ecosystem services and functions. Restoration of marine foundation species has had variable success, especially for seagrasses, where a majority of restoration efforts have failed. While most seagrass restorations track structural attributes over time, rarely do restorations assess the suite of ecological functions that may be affected by restoration. Here we report on the results of two small-scale experimental seagrass restoration efforts in a central California estuary where we transplanted 117 0.25-m2 plots (2,340 shoots) of the seagrass species Zostera marina. We quantified restoration success relative to persistent reference beds, and in comparison to unrestored, unvegetated areas. Within three years, our restored plots expanded ˜8,500%, from a total initial area of 29 to 2,513 m2. The restored beds rapidly began to resemble the reference beds in (1) seagrass structural attributes (canopy height, shoot density, biomass), (2) ecological functions (macrofaunal species richness and abundance, epifaunal species richness, nursery function), and (3) biogeochemical functions (modulation of water quality). We also developed a multifunctionality index to assess cumulative functional performance, which revealed restored plots are intermediate between reference and unvegetated habitats, illustrating how rapidly multiple functions recovered over a short time period. Our comprehensive study is one of few published studies to quantify how seagrass restoration can enhance both biological and biogeochemical functions. Our study serves as a model for quantifying ecosystem services associated with the restoration of a foundation species and demonstrates the potential for rapid functional recovery that can be achieved through targeted restoration of fast-growing foundation species under suitable conditions.

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Emiliania huxleyi biometry and calcification response to the Indian sector of the Southern Ocean environmental gradients

Highlights

  • E. huxleyi morphotypes morphological variations in the SO
  • E. huxleyi extracellular overcalcification prominent in high latitude SO
  • E. huxleyi overcalcified coccosphers show extracellular Ca + Mg precipitation.
  • E. huxleyi may pre-adapted to changing carbonate chemistry.

Abstract

An increase in the atmospheric pCO2 and temperature is expected to reduce ocean CO32− concentration, make oceans warmer and alter ocean circulation patterns. This will also affect the production and biogeographic distribution of marine calcifying organisms including coccolithophores. The lowering of oceanic CO32− is expected to interfere with the coccolithophore calcification process and cause malformation of coccoliths, whereas changes in the oceanic temperature and circulation patterns may shift their biogeographic boundaries. In this study, we have investigated Emiliania huxleyi coccolith and coccosphere size response to the wide-ranging physico-chemical conditions of the Indian sector of the Southern Ocean between latitudes 38oS and 58oS during the austral summer of 2010 (January–February). This study helps to understand the response of E. huxleyi coccolith/coccosphere morphometry and mass changes to the fluctuating temperature, salinity, CO32−, pCO2, and nutrient values. Our results show that in the Indian sector of the Southern Ocean, E. huxleyi coccoliths are larger and coccospheres are smaller in the Subtropical Zone (STZ). In contrast, coccoliths size is smaller and coccospheres size is larger in the Subantarctic Zone (SAZ), which is due to the decrease in Sea Surface Temperature, Sea Surface Salinity and increase in nutrient concentrations. In the Indian sector of the Southern Ocean, E. huxleyi shows a north-to-south morphotype shift from the heavily calcified ‘Group A’ (E. huxleyi morphotype A) to the weakly calcified ‘Group B’ (E. huxleyi morphotypes B/C, C) forms. We demonstrate that although weakly calcified E. huxleyi morphotypes (morphotypes B/C and C) comprise less mass than that of the E. huxleyi morphotype A, due to the large-sized coccospheres and numerous coccoliths per coccosphere, ‘Group B’ coccospheres precipitate large amount of CaCO3 in the SAZ compared to ‘Group A’ coccospheres located in the STZ. We have documented the presence of large E. huxleyi overcalcified coccospheres with large-sized coccoliths in the southernmost cold, high pCO2, and nutrient-rich waters which show extracellular calcite precipitation. The energy dispersive spectrometry analysis indicates the presence of a large amount of Mg in the overcalcified E. huxleyi specimens. We suspect that E. huxleyi in the colder nutrient-rich waters, with future projected changes in the carbonate chemistry, may adapt to low pH, high pCO2 conditions through extracellular Ca and Mg mineralization.

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Molecular basis of ocean acidification sensitivity and adaptation in Mytilus galloprovincialis

One challenge in global change biology is to identify the mechanisms underpinning physiological sensitivities to environmental change and to predict their potential to adapt to future conditions. Using ocean acidification as the representative stressor, molecular pathways associated with abnormal larval development of a globally distributed marine mussel are identified. The targeted developmental stage was the trochophore stage, which is, for a few hours, pH sensitive and is the main driver of developmental success. RNA sequencing and in situ RNA hybridization were used to identify processes associated with abnormal development, and DNA sequencing was used to identify which processes evolve when larvae are exposed to low pH for the full duration of their larval stage. Trochophores exposed to low pH exhibited 43 differentially expressed genes. Thirteen genes, none of which have previously been identified in mussel trochophores, including three unknown genes, were expressed in the shell field. Gene annotation and in situ hybridization point to two core processes associated with the response to low pH: development of the trochophore shell field and the cellular stress response. Encompassing both of these processes, five genes demonstrated changes in allele frequency that are indicative of rapid adaptation. Thus, genes underpinning the most pH-sensitive developmental processes also exhibit scope to adapt via genetic variation currently maintained in the mussel population. These results provide evidence that protecting existing genetic diversity is a critical management action to maximize the potential for rapid adaptation under a changing environment.

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Distribution and abundances of planktic foraminifera and shelled pteropods during the polar night in the sea-ice covered Northern Barents Sea

Planktic foraminfera and shelled pteropods are important calcifying groups of zooplankton in all oceans. Their calcium carbonate shells are sensitive to changes in ocean carbonate chemistry predisposing them as an important indicator of ocean acidification. Moreover, planktic foraminfera and shelled pteropods contribute significantly to food webs and vertical flux of calcium carbonate in polar pelagic ecosystems. Here we provide, for the first time, information on the under-ice planktic foraminifera and shelled pteropod abundance, species composition and vertical distribution along a transect (82°–76°N) covering the Nansen Basin and the northern Barents Sea during the polar night in December 2019. The two groups of calcifiers were examined in different environments in the context of water masses, sea ice cover, and ocean chemistry (nutrients and carbonate system). The average abundance of planktic foraminifera under the sea-ice was low with the highest average abundance (2 ind. m–3) close to the sea-ice margin. The maximum abundances of planktic foraminifera were concentrated at 20–50 m depth (4 and 7 ind. m–3) in the Nansen Basin and at 80–100 m depth (13 ind. m–3) close to the sea-ice margin. The highest average abundance (13 ind. m–3) and the maximum abundance of pteropods (40 ind. m–3) were found in the surface Polar Water at 0–20 m depth with very low temperatures (–1.9 to –1°C), low salinity (<34.4) and relatively low aragonite saturation of 1.43–1.68. The lowest aragonite saturation (<1.3) was observed in the bottom water in the northern Barents Sea. The species distribution of these calcifiers reflected the water mass distribution with subpolar species at locations and depths influenced by warm and saline Atlantic Water, and polar species in very cold and less saline Polar Water. The population of planktic foraminifera was represented by adults and juveniles of the polar species Neogloboquadrina pachyderma and the subpolar species Turborotalita quinqueloba. The dominating polar pteropod species Limacina helicina was represented by the juvenile and veliger stages. This winter study offers a unique contribution to our understanding of the inter-seasonal variability of planktic foraminfera and shelled pteropods abundance, distribution and population size structure in the Arctic Ocean.

Continue reading ‘Distribution and abundances of planktic foraminifera and shelled pteropods during the polar night in the sea-ice covered Northern Barents Sea’

Ocean acidification and bivalve byssus: explaining variable responses using meta-analysis

1. Many bivalve molluscs settle and attach to surfaces using adhesive byssal threads – proteinaceous fibers that together form a network known as the byssus. Since these bivalves rely on byssus for survival, strong byssal attachment promotes a myriad of broad ecological services, including water filtration, nutrient extraction, sediment stabilization, and enhancing biodiversity through habitat creation.

2. Numerous studies have documented weakened byssal attachment strength under ocean acidification (OA); however, a comparable number report no effect, even within the same species. Consequently, whether elevated CO2 levels expected under near-future OA will affect byssal attachment strength in nature remains hotly contested.

3. We used a systematic literature search and meta-analysis to explore factors that could potentially explain observed effect size variation in byssal attachment strength following OA exposure.

4. A systematic literature search uncovered 20 studies experimentally testing the impact of OA on byssal attachment strength (or some proxy thereof). Meta-analysis revealed that body size (mean shell length) was the strongest predictor of effect size variation, with no significant effect of climate, species, year, study temperature, study location, exposure time, food amount, and pH offset. Functionally, a negative linear relationship was observed between body size and effect size.

5. Our finding that the byssal strength of larger bivalves is more susceptible to negative OA effects runs counter to prevailing wisdom that larger, older animals of a given species are more robust to OA than earlier life history stages.

6. This highlights that body size and age may be important factors that determine OA sensitivity in adult calcifiers. In addition to body size, a critical review of each study revealed commonly neglected factors that could influence byssal thread attachment strength which we highlight to provide suggestions for future research in this area.

Supplementary materials

Continue reading ‘Ocean acidification and bivalve byssus: explaining variable responses using meta-analysis’

Effects of flood-associated stressors on growth and survival of early life stage oysters (Crassostrea virginica)

Oyster reefs provide essential ecosystem services but are severely degraded worldwide. Extreme flooding events, which can be intensified by water management decisions, reduce water quality in estuaries and further threaten oyster populations. Restoration and conservation of oysters is dependent on the success of early oyster life stages. This study examined the effect of water quality stressors associated with flooding events on the growth and survival of larval and juvenile oysters (Crassostrea virginica). In 96-h assays, we exposed D-stage larvae to a range of dissolved oxygen, microcystin-LR, pH, and salinity concentrations. These conditions were selected based on water quality data from the Mississippi Sound during a 2019 freshwater flooding event caused by the Bonnet Carré Spillway opening. There was no negative effect of microcystin-LR or pH on early veligers at the concentrations tested, but low salinity significantly reduced shell growth, and hypoxia (< 2 mg L−1 O2) decreased both larval growth and survival. Post-metamorphosis juvenile oysters were exposed to the same water quality stressors for 24 days in the lab. Low DO, pH, and salinity treatments reduced juvenile change in wet weight and shell growth rates, but had no effects on survival. These laboratory-exposed juveniles were subsequently deployed into the field to assess the ability of juveniles to recover from short-term exposure to simulated flooding-associated stressors. After deployment to natural conditions in the Mississippi Sound, juvenile oysters were able to compensate for reduced growth during the lab exposure, even though survival was reduced for juveniles previously exposed to low pH during the first two weeks in the field. In general, early oyster life stages were relatively tolerant of the duration and stressor concentrations tested, but negative sublethal impacts of flood-associated stressors must be considered in the face of increasing frequency and duration of flooding events due to climate change.

Continue reading ‘Effects of flood-associated stressors on growth and survival of early life stage oysters (Crassostrea virginica)’

Lithium elemental and isotope systematics of modern and cultured brachiopods: implications for seawater evolution

Lithium has proven a powerful tracer of weathering processes and chemical seawater evolution. Skeletal components of marine calcifying organisms, and in particular brachiopods, present promising archives of Li signatures. However, Li incorporation mechanisms and potential influence from biological processes or environmental conditions require a careful assessment. In order to constrain Li systematics in brachiopod shells, we present Li concentrations and isotope compositions for 11 calcitic brachiopod species collected from six different geographic regions, paralleled with data from culturing experiments where brachiopods were grown under varying environmental conditions and seawater chemistry (pH–pCO2, temperature, Mg/Ca ratio). The recent brachiopod specimens collected across different temperate and polar environments showed broadly consistent δ7Li values ranging from 25.2 to 28.1‰ (with mean δ7Li of 26.9 ± 1.5‰), irrespective of taxonomic rank, indicating that incorporation of Li isotopes into brachiopod shells is not strongly affected by vital effects related to differences among species. This results in Δ7Licalcite–seawater values (per mil difference in 7Li/6Li between brachiopod calcite shell and seawater) from −2.9‰ to −5.8‰ (with mean Δ7Licalcite–seawater value of −3.6‰), which is larger than the Δ7Licalcite–seawater values calculated based on data from planktonic foraminifera (~0‰ to ~−4‰). This range of values is further supported by results from brachiopods cultured experimentally. Under controlled culturing conditions simulating the natural marine environment, the Δ7Licalcite–seawater for Magellania venosa was −2.5‰ and not affected by an increase in temperature from 10 to 16 °C. In contrast, a decrease in Mg/Ca (or Li/Ca) ratio of seawater by addition of CaCl2 as well as elevated pCO2, and hence low-pH conditions, resulted in an increased Δ7Licalcite-seawater up to −4.6‰. Collectively, our results indicate that brachiopods represent valuable archives and provide an envelope for robust Li-based reconstruction of seawater evolution over the Phanerozoic.

Continue reading ‘Lithium elemental and isotope systematics of modern and cultured brachiopods: implications for seawater evolution’

Decrease in volume and density of foraminiferal shells with progressing ocean acidification

Rapid increases in anthropogenic atmospheric CO2 partial pressure have led to a decrease in the pH of seawater. Calcifying organisms generally respond negatively to ocean acidification. Foraminifera are one of the major carbonate producers in the ocean; however, whether calcification reduction by ocean acidification affects either foraminiferal shell volume or density, or both, has yet to be investigated. In this study, we cultured asexually reproducing specimens of Amphisorus kudakajimensis, a dinoflagellate endosymbiont-bearing large benthic foraminifera (LBF), under different pH conditions (pH 7.7–8.3, NBS scale). The results suggest that changes in seawater pH would affect not only the quantity (i.e., shell volume) but also the quality (i.e., shell density) of foraminiferal calcification. We proposed that pH and temperature affect these growth parameters differently because (1) they have differences in the contribution to the calcification process (e.g., Ca2+-ATPase and Ω) and (2) pH mainly affects calcification and temperature mainly affects photosynthesis. Our findings also suggest that, under the IPCC RCP8.5 scenario, both ocean acidification and warming will have a significant impact on reef foraminiferal carbonate production by the end of this century, even in the tropics.

Continue reading ‘Decrease in volume and density of foraminiferal shells with progressing ocean acidification’

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