Posts Tagged 'annelids'

Current and future trophic interactions in tropical shallow-reef lagoon habitats

Calcium carbonate (CaCO3) sediments are the dominant form of CaCO3 on coral reefs accumulating in lagoon and inter-reefal areas. Owing to their mineralogy and a range of physical parameters, tropical CaCO3 sediments are predicted to be more sensitive to dissolution driven by ocean acidification than the skeleton of living reef organisms. How this scales up to impact infaunal organisms, which are an important food source for higher trophic levels, and thereby ecosystem functioning, is not well explored. We combined seasonal field surveys in a shallow-reef lagoon ecosystem on the Great Barrier Reef, Australia, with stable isotope analyses and a tank-based experiment to examine the potential top-down influence of the deposit-feeding sea cucumber, Stichopus herrmanni, on this infaunal community under current and future ocean pH. Densities of surface-sediment meiofauna were lowest in winter and spring, with harpacticoid copepods (38%) and nematodes (27%) the dominant taxa. Stable isotope analyses showed that S. herrmanni had a top-down influence on meiofauna and microphytes with a distinct δ13C and δ15N trophic position that was homogenous across seasons and locations. Tanks that mimicked sandy shallow-reef lagoon habitats were used to examine the effects of ocean acidification (elevated pCO2) on this trophic interaction. We used outdoor control (sediment only) and experimental (sediment plus S. herrmanni) tanks maintained at present-day and near-future pCO2 (+ 570 µatm) for 24 days, which fluctuated with the diel pCO2 cycle. In sediment-only tanks, copepods were > twofold more abundant at elevated pCO2, with no negative effects documented for any meiofauna group. When included in the community, top-down control by S. herrmanni counteracted the positive effects of low pH on meiofaunal abundance. We highlight a novel perspective in coral reef trophodynamics between surface-sediment meiofauna and deposit-feeding sea cucumbers, and posit that community shifts may occur in shallow-reef lagoon habitats in a future ocean with implications for the functioning of coral reefs from the bottom up.

Continue reading ‘Current and future trophic interactions in tropical shallow-reef lagoon habitats’

Experimental evidence of uncertain future of the keystone ragworm Hediste diversicolor (O.F. Müller, 1776) under climate change conditions

Highlights

  • Temperature enhances the impact of acidification on polychaetes survival and burrowing behavior.
  • Regardless the temperature, acidification results in a reduction on polychaetes feeding rate
  • Faster regeneration at the lowest temperature and less regenerated chaetigers at lower pH levels
  • Climate change induced oxidative stress in H. diversicolor
  • Polychaetes metabolic capacity was enhanced in stressed organisms, with no expenditure of energy reserves.

Abstract

It is currently assumed that climate change related factors pose severe challenges to biodiversity maintenance. This paper assesses the multi-stressor effects of elevated temperature (15 °C as control, 25 °C as elevated) and CO2 levels (pH 8.1 as control, 7.5 and 7.0 representing acidifying conditions) on the physiological (survival, and regenerative capacity), behavioral (feeding and burrowing activities), and biochemical changes (metabolic capacity, oxidative status and biotransformation mechanisms) experienced by the keystone polychaete Hediste diversicolor. Temperature rise enlarged the adverse effect of marine acidification on the survival of H. diversicolor, delayed the beginning of the excavation activity, enhancing the negative effects that pH decrease had in the burrowing behavior of this polychaete. Additionally, regardless of the temperature, exposure of H. diversicolor to acidification results in a reduction in the feeding rate. It is the first time that this decreased feeding capacity is found related to seawater acidification in this species. The healing of the wound and the blastemal formation were retarded due to these two climatic factors which hinder the regenerative process of polychaetes. These vital physiological functions of H. diversicolor can be related to the oxidative stress induced by climate change conditions since free radicals overproduced will impair cells functioning affecting species biochemical and physiological performance, including feeding, and tissue regeneration. The present results also demonstrated that although polychaete’s metabolic capacity was enhanced under stress conditions, organisms were still able to increase or maintain their energy reserves. Our findings are of major environmental relevance considering that predicted climate change conditions will affect species vital and ecological and physiological capacities. These can be translated into shrinking not only at the individual and population level but also in microbial and endofaunal diversities, in the detritus processing in estuaries and biogeochemical cycles at the ecosystem level. Thus the conservation of H. diversicolor populations is vital for the normal functioning of estuarine mudflat ecosystems.

Continue reading ‘Experimental evidence of uncertain future of the keystone ragworm Hediste diversicolor (O.F. Müller, 1776) under climate change conditions’

Fluctuating seawater pCO2/pH induces opposing interactions with copper toxicity for two intertidal invertebrates

Highlights

• Fluctuating pCO2/pH doubled copper-induced antioxidant activity and DNA damage in mussels.

• In contrast, fluctuating conditions mitigated some of the effects of copper for ragworms.

• These effects were associated with the differing acid-base physiology of the two species.

• Physiology was as important as changing copper chemistry in determining overall toxicity.

Abstract

Global ocean pCO2 is increasing as a result of anthropogenic CO2 emissions, driving a decline in seawater pH. However, coastal waters already undergo fluctuations in pCO2/pH conditions over far shorter timescales, with values regularly exceeding those predicted for the open ocean by the year 2100. The speciation of copper, and therefore its potential toxicity, is affected by changing seawater pH, yet little is known concerning how present-day natural fluctuations in seawater pH affect copper toxicity to marine biota. Here, we test the hypothesis that a fluctuating seawater pCO2/pH regime will alter the responses of the mussel Mytilus edulis and the ragworm Alitta virens to sub-lethal copper, compared to a static seawater pCO2/pH scenario. Mussels and worms were exposed to 0.1 and 0.25 μM copper respectively, concentrations determined to produce comparable toxicity responses in these species, for two weeks under a fluctuating 12-hour pCO2/pH cycle (pH 8.14–7.53, pCO2 445–1747 μatm) or a static pH 8.14 (pCO2 432 μatm) treatment. Mussels underwent a haemolymph acidosis of 0.1–0.2 pH units in the fluctuating treatments, alongside two-fold increases in the superoxide dismutase activity and DNA damage induced by copper, compared to those induced by copper under static pH conditions. Conversely, ragworms experienced an alkalosis of 0.3 pH units under fluctuating pH/pCO2, driven by a two-fold increase in coelomic fluid bicarbonate. This mitigated the copper-induced oxidative stress to slightly reduce both antioxidant activity and DNA damage, relative to the static pH + copper treatment. These opposing responses suggest that differences in species acid-base physiology were more important in determining toxicity responses than the pH-induced speciation change. With variability in seawater chemistry predicted to increase as climate change progresses, understanding how fluctuating conditions interact with the toxicity of pH-sensitive contaminants will become more crucial in predicting their risk to coastal biota.

Continue reading ‘Fluctuating seawater pCO2/pH induces opposing interactions with copper toxicity for two intertidal invertebrates’

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’

Multimarker response of the ragworm Hediste diversicolor (Polychaeta) to seawater acidification derived from potential CO2 leakage from the CCS sub-seabed storage site in the Baltic Sea

Highlights

• Seawater acidification affected physiological traits, LPO and growth of Hediste diversicolor from the southern Baltic Sea.

• Moderate hypercapnia (pH 7.5–7.1) induced an increase in metabolic rate of the polychaetes and a decline of their growth.

• The most acidic environment (pH 6.5) caused metabolic slow down limiting energy turnover and growth.

• Reduced seawater pH did not impact energetic reserves so, proteins were not used as substrates under acidic conditions.

• High tolerance of the ragworms to hypercapnia stems probably from pre-adaptation to natural pH reduction events in sediment.

Abstract

Sub-seabed Carbon Capture and Storage (CCS) is conceived as safe technology with small likehood of negative consequences to the marine ecosystem but CO2 escape from geological reservoir still poses potential environmental risk. If carbon dioxide leakage occurs carbonate chemistry in the bottom zone and sessile benthic fauna are expected to be the most likely affected by elevated levels of CO2. Though generic mechanisms and advisory conclusions on the presumable impact of increased acidity on the marine benthic biota were formulated they cannot be applied uniformly across different environmental variables as specific local conditions may alter biological response to hypercapnia. A laboratory experiment was conducted to quantify the effects of medium-term (8 wk) exposure to seawater acidification (pH 7.7–6.5) on the infaunal polychaete Hediste diversicolor from the southern Baltic Sea using multimarker approach. Under moderate acidity (pH 7.5 and 7.1) the polychaetes were found to increase metabolic rate (by 13.4% and 19.6%, respectively) and reduce their body mass (by 8.1% and 5.5% wet weight, respectively and by 6.1% and 3.0% dry weight, respectively) whilst enhancing synthesis of antioxidant malondialdehyde (by 22.8% and 65.3%, respectively). In the most acidic environment (pH 6.5) the ragworms showed overall metabolic slow down (by 34.8%) and impaired growth (e.g. by 10.2% for length of the first three segments) indicative of low vulnerability to hypercapnia. High implicit tolerance of the polychaetes to increased acidity in the environment stems inevitably from a certain level of pre-adaptation to pH reduction events which occur in organic-rich stratified sediments due to intense aerobic biomineralization leading often to oxygen depletion and formation of toxic hydrogen sulphide. Acidification did not affect energetic reserves suggesting that costs of acid-base maintenance were covered mainly from assimilated food and that proteins were not used as metabolic substrates.

Continue reading ‘Multimarker response of the ragworm Hediste diversicolor (Polychaeta) to seawater acidification derived from potential CO2 leakage from the CCS sub-seabed storage site in the Baltic Sea’

Ocean acidification alters the responses of invertebrates to wound-activated infochemicals produced by epiphytes of the seagrass Posidonia oceanica

Highlights

• First time evaluation of the effect of infochemicals produced at two pH by the epiphytic community and by selected diatoms.

• O.A. alters the fine-tuned chemical cross-talks between seagrass epiphytes and associated invertebrates.

• Algae play their roles at different concentrations and convey different messages to associated animal communities.

• O.A. has consequences on the structure of associated communities and food webs of seagrass ecosystems.

Abstract

Ocean acidification (OA) influences the production of volatile organic compounds (VOCs) by seagrass leaves and their associated epiphytes. We hypothesize that the perception of “odour” produced by seagrass leaf epiphytes will change with seawater acidification, affecting the behaviour of seagrass-associated invertebrates. To test this hypothesis, we collected epiphytes from leaves of Posidonia oceanica growing at two pH conditions (7.7 and 8.1) and identified the most abundant genera of diatoms. We tested the VOCs produced at pH 8.1 by the epiphytic communities in toto, as well as those produced by selected diatoms, on various invertebrates. A complex set of species-specific and concentration-dependent chemotactic reactions was recorded, according to the pH of seawater. In particular, VOCs produced by individual diatoms triggered contrasting reactions in invertebrates, depending on the pH. The perception of epiphyte VOCs is likely to vary due to alteration of species ability to perceive and/or interpret chemical cues as infochemicals or due to changes in the structure of VOCs themselves. Thus, OA alters the fine-tuned chemical cross-talks between seagrass epiphytes and associated invertebrates, with potential consequences for the structure of communities and food webs of seagrass ecosystems.

Continue reading ‘Ocean acidification alters the responses of invertebrates to wound-activated infochemicals produced by epiphytes of the seagrass Posidonia oceanica’

Evolutionary links between intra‐ and extracellular acid–base regulation in fish and other aquatic animals

The acid–base relevant molecules carbon dioxide (CO2), protons (H+), and bicarbonate (HCO3) are substrates and end products of some of the most essential physiological functions including aerobic and anaerobic respiration, ATP hydrolysis, photosynthesis, and calcification. The structure and function of many enzymes and other macromolecules are highly sensitive to changes in pH, and thus maintaining acid–base homeostasis in the face of metabolic and environmental disturbances is essential for proper cellular function. On the other hand, CO2, H+, and HCO3 have regulatory effects on various proteins and processes, both directly through allosteric modulation and indirectly through signal transduction pathways. Life in aquatic environments presents organisms with distinct acid–base challenges that are not found in terrestrial environments. These include a relatively high CO2 relative to O2 solubility that prevents internal CO2/HCO3 accumulation to buffer pH, a lower O2 content that may favor anaerobic metabolism, and variable environmental CO2, pH and O2 levels that require dynamic adjustments in acid–base homeostatic mechanisms. Additionally, some aquatic animals purposely create acidic or alkaline microenvironments that drive specialized physiological functions. For example, acidifying mechanisms can enhance O2 delivery by red blood cells, lead to ammonia trapping for excretion or buoyancy purposes, or lead to CO2 accumulation to promote photosynthesis by endosymbiotic algae. On the other hand, alkalinizing mechanisms can serve to promote calcium carbonate skeletal formation. This nonexhaustive review summarizes some of the distinct acid–base homeostatic mechanisms that have evolved in aquatic organisms to meet the particular challenges of this environment.

Continue reading ‘Evolutionary links between intra‐ and extracellular acid–base regulation in fish and other aquatic animals’

Toward a mechanistic understanding of marine invertebrate behavior at elevated CO2

Elevated carbon dioxide (CO2) levels can alter ecologically important behaviors in a range of marine invertebrate taxa; however, a clear mechanistic understanding of these behavioral changes is lacking. The majority of mechanistic research on the behavioral effects of elevated CO2 has been done in fish, focusing on disrupted functioning of the GABAA receptor (a ligand-gated ion channel, LGIC). Yet, elevated CO2 could induce behavioral alterations through a range of mechanisms that disturb different components of the neurobiological pathway that produces behavior, including disrupted sensation, altered behavioral choices and disturbed LGIC-mediated neurotransmission. Here, we review the potential mechanisms by which elevated CO2 may affect marine invertebrate behaviors. Marine invertebrate acid–base physiology and pharmacology is discussed in relation to altered GABAA receptor functioning. Alternative mechanisms for behavioral change at elevated CO2 are considered and important topics for future research have been identified. A mechanistic understanding will be important to determine why there is variability in elevated CO2-induced behavioral alterations across marine invertebrate taxa, why some, but not other, behaviors are affected within a species and to identify which marine invertebrates will be most vulnerable to rising CO2 levels.

Continue reading ‘Toward a mechanistic understanding of marine invertebrate behavior at elevated CO2’

Energetic context determines species and community responses to ocean acidification

Physiological responses to ocean acidification are thought to be related to energetic trade‐offs. Although a number of studies have proposed that negative responses to low pH could be minimized in situations where food resources are more readily available, evidence for such effects on individuals remain mixed, and the consequences of such effects at the community level remain untested. We explored the potential for food availability and diet quality to modify the effects of acidification on developing marine fouling communities in field‐deployed mesocosms by supplementing natural food supply with one of two species of phytoplankton, differing in concentration of fatty acids. After twelve weeks, no species demonstrated the interactive effects generally predicted in the literature, where a positive overall effect of diet mitigated the negative overall effects of acidification. Rather, for some species, additional food supply appeared to bring out or exacerbate the negative effects of low pH. Community richness and structure were only altered by acidification, while space occupation and evenness reflected patterns of the most dominant species. Importantly, we find that acidification stress can increase the relative abundance of invasive species, even under resource conditions that otherwise prevented invasive species establishment. Overall, the proposed hypothesis regarding the ability for food addition to mitigate the negative effects of acidification is thus far not widely supported at species or community levels. It is clear that acidification is a strong driving force in these communities but understanding underlying energetic and competitive context is essential to developing mechanistic predictions for climate change responses.

Continue reading ‘Energetic context determines species and community responses to ocean acidification’

Transcriptome analysis of the Nematode Caenorhabditis elegans in acidic stress environments

Ocean acidification and acid rain, caused by modern industrial fossil fuels burning, lead to decrease of living environmental pH, which results in a series of negative effects on many organisms. However, the underlying mechanisms of animals’response to acidic pH stress are largely unknown. In this study, we used the nematode Caenorhabditis elegans as an animal model to explore the regulatory mechanisms of organisms’response to pH decline. Two major stress-responsive pathways were found through transcriptome analysis in acidic stress environments. Firstly, when the pH dropped from 6.33 to 4.33, the worms responded to the pH stress by up-regulation of the col, nas and dpy genes, which are required for cuticle synthesis and structure integrity. Secondly, when the pH continued to decrease from 4.33, the metabolism of xenobiotics by cytochrome P450 pathway genes (cyp, gst, ugt, and ABC transporters) played a major role in protecting the nematodes from the toxic substances probably produced by the more acidic environment. At the same time, cuticle synthesis slowed down might due to its insufficient protective ability. Moreover, the systematic regulation pattern we found in nematodes, might also be applied to other invertebrate and vertebrate animals to survive in the changing pH environments. Thus, our data might lay the foundation to identify the master gene(s) responding and adaptation to acidic pH stress in further studies, and might also provide new solutions to improve assessment and monitoring of ecological restoration outcomes, or generate novel genotypes via genome editing for restoring in challenging environments especially in the context of acidic stress through global climate change.

Continue reading ‘Transcriptome analysis of the Nematode Caenorhabditis elegans in acidic stress environments’


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