Posts Tagged 'biological response'

Functional diversity and metabolic response in benthic communities along an ocean acidification gradient

Published 1 May 2024 Science Leave a Comment
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Highlights

  • Ocean acidification (OA) affect the distribution of traits within a community leading to the selection of specific functional traits.
  • Along with the selection of traits, OA led to differences in oxygen consumption between benthic communities following acidification gradient.
  • Altered acidified condition have a negative effect on the stability of the community resulting from changes in functional evennes of benthic communities.

Abstract

Altered ocean chemistry caused by ocean acidification (OA) is expected to have negative repercussions at different levels of the ecological hierarchy, starting from the individual and scaling up to the community and ultimately to the ecosystem level. Understanding the effects of OA on benthic organisms is of primary importance given their relevant ecological role in maintaining marine ecosystem functioning. The use of functional traits represents an effective technique to investigate how species adapt to altered environmental conditions and can be used to predict changes in the resilience of communities faced with stresses associated with climate change. Artificial supports were deployed for 1-y along a natural pH gradient in the shallow hydrothermal systems of the Bottaro crater near Panarea (Aeolian Archipelago, southern Tyrrhenian Sea), to explore changes in functional traits and metabolic rates of benthic communities and the repercussions in terms of functional diversity. Changes in community composition due to OA were accompanied by modifications in functional diversity. Altered conditions led to higher oxygen consumption in the acidified site and the selection of species with the functional traits needed to withstand OA. Calcification rate and reproduction were found to be the traits most affected by pH variations. A reduction in a community’s functional evenness could potentially reduce its resilience to further environmental or anthropogenic stressors. These findings highlight the ability of the ecosystem to respond to climate change and provide insights into the modifications that can be expected given the predicted future pCO2 scenarios. Understanding the impact of climate change on functional diversity and thus on community functioning and stability is crucial if we are to predict changes in ecosystem vulnerability, especially in a context where OA occurs in combination with other environmental changes and anthropogenic stressors.

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Effect of increased CO2 on calcium homeostasis and signaling in a marine diatom

Published 30 April 2024 Science Leave a Comment
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Ocean acidification influences photosynthesis, respiration, and metabolism in marine diatoms, leading to changes in diatom growth performance and shifts in phytoplankton communities. Previous studies have demonstrated that increases in seawater CO2 concentrations affect the uptake of trace metals such as iron, zinc, copper, and cobalt by marine diatoms. However, the influence of increased CO2 on calcium, which plays a vital role as a secondary messenger in various signaling pathways within organisms, has received limited attention so far. This study examined the effect of increased CO2 on Ca homeostasis and signaling in the marine diatom Phaeodactylum tricornutum. While seawater acidification had little effect on the diatom’s growth, it significantly changed cell properties (surface topography, adhesion, and surface potential). Elevated CO2 concentrations reduced calcium accumulation P. tricornutum and lowered the rise of cytosolic Ca2+ transients stimulated by toxic aldehyde, phosphorus supplement, and hypo-osmotic stress. Our results suggest that a continuous rise in atmospheric CO2 may alter diatoms’ response to environmental cues.

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Effects of ocean acidification and summer thermal stress on the physiology and growth of the atlantic surfclam (Spisula solidissima)

Published 29 April 2024 Science Leave a Comment
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This study examines the physiological response of the Atlantic surfclam (Spisula solidissima) to ocean acidification in warm summer temperatures. Working with ambient seawater, this experiment manipulated pH conditions while maintaining natural diel fluctuations and seasonal shifts in temperature. One-year-old surfclams were exposed to one of three pH conditions (ambient (control): 7.8 ± 0.07, medium: 7.51 ± 0.10, or low: 7.20 ± 0.10) in flow-through conditions for six weeks, and feeding and digestive physiology was measured after one day, two weeks, and six weeks. After six weeks of exposure to medium and low pH treatments, growth was not clearly affected, and, contrastingly, feeding and digestive physiology displayed variable responses to pH over time. Seemingly, low pH reduced feeding and absorption rates compared to both the medium treatment and ambient (control) condition; however, this response was clearer after two weeks compared to one day. At six weeks, suppressed physiological rates across both pH treatments and the ambient condition suggest thermal stress from high ambient water temperatures experienced the week prior (24–26 °C) dominated over any changes from low pH. Results from this study provide important information about reduced energy acquisition in surfclams in acidified environments and highlight the need for conducting multistressor experiments that consider the combined effects of temperature and pH stress.

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Geochemical evidence of temporal ecosystem photosynthetic plasticity within a pristine coral atoll

Published 29 April 2024 Science Leave a Comment
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The impacts of ocean acidification on coral reef macroalgal community composition and metabolism have implications for the habitat supporting capacity of future reefs. In this pilot study, we use co-located semi-hourly measurements of total dissolved inorganic carbon (DIC), total alkalinity, and the stable carbon isotope composition of DIC (δ13CDIC) over a 27 + h period from Tetiaroa Atoll, French Polynesia, to investigate the potential for reef carbonate chemistry to record information related to benthic photosynthetic community composition and response to natural gradients in ambient acidity and dissolved carbon dioxide. The results of this preliminary sampling and modeling exercise suggest that Tetiaroa’s macroalgal communities express plastic carbon-concentrating mechanisms (CCMs) over daily cycles of productivity but may potentially vary this expression as a function of ambient CO2 and acidity within the ecosystem. Additional studies are, therefore, underway to investigate the implications of these observations for reef macroalgal compositional differences under rapidly acidifying oceans.

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Influencing intertidal food web: implications of ocean acidification on the physiological energetics of key species the ‘wedge’ clam Donax faba

Published 26 April 2024 Science Leave a Comment
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Highlights

  • Daily growth rate & calcium concentration have significantly decreased in acidified condition.
  • Total antioxidants and antioxidant enzymes showed an upward tendency.
  • Nutrient composition in clams has altered in acidified condition compared to control.
  • Prolonged exposure to OA will cause deleterious effects on clams thereby upsetting the intertidal food chain.

Abstract

Ocean acidification has become increasingly severe in coastal areas. It poses emerging threats to coastal organisms and influences ecological functioning. Donax faba, a dominant clam in the intertidal zone of the Bay of Bengal, plays an important role in the coastal food web. This clam has been widely consumed by the local communities and also acts as a staple diet for shorebirds and crustaceans. In this paper, we investigated how acidified conditions will influence the physiology, biochemical constituents, and energetics of Donax faba. Upon incubation for 2 months in lowered pH 7.7 ± 0.05 and control 8.1 ± 0.05 conditions, we found a delayed growth in the acidified conditions followed by decrease in calcium ions in the clam shell. Although not significant, we found the digestive enzymes showed a downward trend. Total antioxidant was significantly increased in the acidified condition compared to the control. Though not significant, the expression level of MDA and antioxidant enzymes (SOD, CAT, GST, GPX, and APX) showed increasing trend in acidified samples. Among nutrients such as amino acids and fatty acids, there was no significant difference between treatments, however, showed a downward trend in the acidified conditions compared to control. Among the minerals, iron and zinc showed significant increase in the acidified conditions. The above results suggest that the clam growth, and physiological energetics may have deleterious effects if exposed for longer durations at lowered pH condition thereby affecting the organisms involved in the coastal food web.

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Antagonistic interactions of the dinoflagellate Alexandrium catenella under simultaneous warming and acidification

Published 26 April 2024 Science Leave a Comment
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Highlights

  • We present novel findings of the angatonistic effects of Alexandrium catenella on phytoplankton under warming and acidification.
  • Experiments targeted three species and tested for density-dependent effects.
  • Growth inhibition increased under warming and acidification on Rhodomonas salina and Tetraselmis.
  • There was no antagonistic effect on the target diatom (Thalassiosira weissflogii) under ambient or OWA conditions.
  • Growth inhibition under OWA conditions may alter phytoplankton community composition by affecting some groups but not others.

Abstract

There is a concern that harmful algal bloom (HAB) species may increase under climate change. Yet, we lack understanding of how ecological interactions will be affected under ocean warming and acidification (OWA) conditions. We tested the antagonistic effects of three strains of the dinoflagellate HAB species Alexandrium catenella on three target species (the chlorophyte Tetraselmis sp., the cryptomonad Rhodomonas salina, and the diatom Thalassiosira weissflogii) at various biomass ratios between species, at ambient (16 °C and 400 µatm CO2) and OWA (20 °C and 2000 µatm CO2) conditions. In these experiments the Alexandrium strains had been raised under OWA conditions for ∼100 generations. All three non-HAB species increased their growth rate under OWA relative to ambient conditions. Growth rate inhibition was evident for R. salina and Tetraselmis sp. under OWA conditions, but not under ambient conditions. These negative effects were exacerbated at higher concentrations of Alexandrium relative to non-HAB species. By contrast, T. weissflogii showed positive growth in the presence of two strains of Alexandrium under ambient conditions, whereas growth was unaffected under OWA. Contrary to our expectations, A. catenella had a slight negative response in the presence of the diatom. These results demonstrate that Alexandrium exerts higher antagonistic effects under OWA compared to ambient conditions, and these effects are species-specific and density dependent. These negative effects may shift phytoplankton community composition under OWA conditions.

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Transgenerational acclimation to acidified seawater and gene expression patterns in a sea urchin

Published 26 April 2024 Science Leave a Comment
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Highlights

  • Transgenerational response to ocean acidification reduces prediction uncertainty.
  • Two-generations experiment with mature sea urchin was conducted in acidified seawater.
  • Acclimated parent larvae showed higher survival, less size reduction in acidified water.
  • Different gene expressions were observed in larvae from acclimated/non-acclimated parents.

Abstract

Transgenerational responses of susceptible calcifying organisms to progressive ocean acidification are an important issue in reducing uncertainty of future predictions. In this study, a two-generation rearing experiment was conducted using mature Mesocentrotus nudus, a major edible sea urchin that occurs along the coasts of northern Japan. Morphological observations and comprehensive gene expression analysis (RNA-seq) of resulting larvae were performed to examine transgenerational acclimation to acidified seawater. Two generations of rearing experiments showed that larvae derived from parents acclimated to acidified seawater tended to have higher survival and show less reduction in body size when exposed to acidified seawater of the same pH, suggesting that a positive carry-over effect occurred. RNA-seq analysis showed that gene expression patterns of larvae originated from both acclimated and non-acclimated parents to acidified seawater tended to be different than control condition, and the gene expression pattern of larvae originated from acclimated parents was substantially different than that of larvae of non-acclimated and control parents.

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Using museum collections to assess the impact of industrialization on mussel (Mytilus edulis) calcification

Published 23 April 2024 Science Leave a Comment
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Mytilus edulis is a commercially and ecologically important species found along the east coast of the United States. Ecologically, M. edulis improves water quality through filtration feeding and provides habitat formation and coastal protection through reef formation. Like many marine calcifiers, ocean warming, and acidification are a growing threat to these organisms—impacting their morphology and function. Museum collections are useful in assessing long-term environmental impacts on organisms in a natural multi-stressor environment, where acclimation and adaptation can be considered. Using the American Museum of Natural History collections ranging from the early 1900s until now, we show that shell porosity changes through time. Shells collected today are significantly more porous than shells collected in the 1960s and, at some sites, than shells collected from the early 1900s. The disparity between porosity changes matches well with the warming that occurred over the last 130 years in the north Atlantic suggesting that warming is causing porosity changes. However, more work is required to discern local environmental impacts and to fully identify porosity drivers. Since, porosity is known to affect structural integrity, porosity increasing through time could have negative consequences for mussel reef structural integrity and hence habitat formation and storm defenses.

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Decline of a distinct coral reef holobiont community under ocean acidification

Published 22 April 2024 Science Leave a Comment
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Background

Microbes play vital roles across coral reefs both in the environment and inside and upon macrobes (holobionts), where they support critical functions such as nutrition and immune system modulation. These roles highlight the potential ecosystem-level importance of microbes, yet most knowledge of microbial functions on reefs is derived from a small set of holobionts such as corals and sponges. Declining seawater pH — an important global coral reef stressor — can cause ecosystem-level change on coral reefs, providing an opportunity to study the role of microbes at this scale. We use an in situ experimental approach to test the hypothesis that under such ocean acidification (OA), known shifts among macrobe trophic and functional groups may drive a general ecosystem-level response extending across macrobes and microbes, leading to reduced distinctness between the benthic holobiont community microbiome and the environmental microbiome.

Results

We test this hypothesis using genetic and chemical data from benthic coral reef community holobionts sampled across a pH gradient from CO2 seeps in Papua New Guinea. We find support for our hypothesis; under OA, the microbiome and metabolome of the benthic holobiont community become less compositionally distinct from the sediment microbiome and metabolome, suggesting that benthic macrobe communities are colonised by environmental microbes to a higher degree under OA conditions. We also find a simplification and homogenisation of the benthic photosynthetic community, and an increased abundance of fleshy macroalgae, consistent with previously observed reef microbialisation.

Conclusions

We demonstrate a novel structural shift in coral reefs involving macrobes and microbes: that the microbiome of the benthic holobiont community becomes less distinct from the sediment microbiome under OA. Our findings suggest that microbialisation and the disruption of macrobe trophic networks are interwoven general responses to environmental stress, pointing towards a universal, undesirable, and measurable form of ecosystem change.

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Interactive effects of chronic ocean acidification and warming on the growth, survival, and physiological responses of adults of the temperate sea urchin Strongylocentrotus intermedius

Published 19 April 2024 Science Leave a Comment
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Highlights

  • Ocean acidification and warming (OAW) repressed the survival and growth of Strongylocentrotus intermedius.
  • OAW altered the relative expression and activities of key metabolic enzymes of S. intermedius.
  • OAW attenuated the ATP production and antioxidant capability of S. intermedius.
  • Interactive effects of OAW on S. intermedius were analyzed in detail.

Abstract

To investigate the interactive effects of chronic ocean acidification and warming (OAW) on the growth, survival, and physiological responses of sea urchins, adults of the temperate sea urchin Strongylocentrotus intermedius were incubated separately/jointly in acidic (ΔpHNBS = −0.5 units) and thermal (ΔT = +3.0 °C) seawater for 120 days under lab-controlled conditions based on the projected ocean pH and temperature for 2100 put forward by the Intergovernmental Panel on Climate Change (IPCC). Survival rate (SR), average food consumption rate (FCR), gut index (GuI), specific growth rate (SGR), digestive capability, energy production, and antioxidant capability were subsequently determined. The results showed that 1) the SR, FCR, GuI and SGR decreased sharply under OAW conditions. Significant interactive effects of OAW on SR and SGR were observed at 120 days post-incubation (dpi), and on FCR this occurred at 90 dpi. 2) OAW altered the activities of both digestive and antioxidant enzymes. There were significant interaction effects of OAW on the activities of amylase, trehalase, and superoxide dismutase. 3) The relative gene expression levels and activities of key enzymes involved in glycometabolism pathways (i.e., glycolysis and the tricarboxylic acid cycle) were significantly affected by OAW, resulting in an alteration of the total ATP content in the sea urchins. Interaction effects of OAW were observed in both relative gene expression and the activity of enzymes involved in glycolysis (hexokinase), the transformation of glycolysis end-products (lactate dehydrogenase), the tricarboxylic acid cycle (citrate synthetase), and ATP production (Na+/K+-ATPase). The data from this study will enrich our knowledge concerning the combined effects of global climate change on the survival, growth, and physiological responses of echinoderms.

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Biological response of eelgrass epifauna, Taylor’s sea hare (Phyllaplysia taylori) and eelgrass isopod (Idotea resecata), to elevated ocean alkalinity

Published 18 April 2024 Science Leave a Comment
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Marine carbon dioxide removal (mCDR) approaches are under development to mitigate the effects of climate change with potential co-benefits of local reduction of ocean acidification impacts. One such method is ocean alkalinity enhancement (OAE). A specific OAE method that avoids issues of solid dissolution kinetics and the release of impurities into the ocean is the generation of aqueous alkalinity via electrochemistry to enhance the alkalinity of the surrounding water and extract acid from seawater. While electrochemical acid extraction is a promising method for increasing the carbon dioxide sequestration potential of the ocean, the biological effects of this method are relatively unknown. This study aims to address this knowledge gap by testing the effects of increased pH and alkalinity, delivered in the form of aqueous base, on two ecologically important eelgrass epifauna in the U.S. Pacific Northwest, Taylor’s sea hare (Phyllaplysia taylori) and eelgrass isopod (Idotea resecata), across pH treatments ranging from 7.8 to 9.3. Four-day experiments were conducted in closed bottles to allow measurements of the evolution of carbonate species throughout the experiment with water refreshed twice daily to maintain elevated pH. Sea hares experienced mortality in all pH treatments, ranging from 40 % mortality at pH 7.8 to 100 % mortality at pH 9.3. Isopods experienced lower mortality rates in all treatment groups, which did not significantly increase with higher pH treatments. Different invertebrate species will likely have different responses to increased pH and alkalinity, depending on their physiological vulnerabilities. Investigation of the potential vulnerabilities of local marine species will help inform the decision-making process regarding mCDR planning and permitting.

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Ocean acidification significantly alters the trace element content of the kelp, Saccharina latissima

Published 17 April 2024 Science Closed
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Highlights

  • Exposure of S. latissima to higher concentrations of pCO2 caused a significant increase in the content and subcellular heterogeneity of iodine and arsenic in kelp.
  • The iodine-to‑calcium and bromine-to‑calcium ratios of kelp increased significantly under high CO2.
  • High CO2 significantly reduced levels of copper and cadmium in kelp tissue.
  • The elemental content of seaweeds used as food should be carefully monitored as climate change accelerates this century.

Abstract

Seaweeds are ecosystem engineers that can serve as habitat, sequester carbon, buffer ecosystems against acidification, and, in an aquaculture setting, represent an important food source. One health issue regarding the consumption of seaweeds and specifically, kelp, is the accumulation of some trace elements of concern within tissues. As atmospheric CO2 concentrations rise, and global oceans acidify, the concentrations of elements in seawater and kelp may change. Here, we cultivated the sugar kelp, Saccharina latissima under ambient (~400 μatm) and elevated pCO2 (600–2400 μatm) conditions and examined the accumulation of trace elements using x-ray powder diffraction, sub-micron resolution x-ray imaging, and inductively coupled plasma mass spectrometry. Exposure of S. latissima to higher concentrations of pCO2 and lower pH caused a significant increase (p < 0.05) in the iodine and arsenic content of kelp along with increased subcellular heterogeneity of these two elements as well as bromine. The iodine-to‑calcium and bromine-to‑calcium ratios of kelp also increased significantly under high CO2/low pH (p < 0.05). In contrast, high CO2/low pH significantly reduced levels of copper and cadmium in kelp tissue (p < 0.05) and there were significant inverse correlations between concentrations of pCO2 and concentrations of cadmium and copper in kelp (p < 0.05). Changes in copper and cadmium levels in kelp were counter to expected changes in their free ionic concentrations in seawater, suggesting that the influence of low pH on algal physiology was an important control on the elemental content of kelp. Collectively, these findings reveal the complex effects of ocean acidification on the elemental composition of seaweeds and indicate that the elemental content of seaweeds used as food must be carefully monitored as climate change accelerates this century.

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Ocean acidification offsets the effect of warming on sediment denitrification and associated nitrous oxide production

Published 16 April 2024 Science Closed
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Rates of denitrification and associated nitrous oxide (N2O) production are expected to increase with global warming, leading to positive climate feedback. However, previous studies have not considered the combined effect of ocean acidification (OA, pCO2 ~ 900 µatm) and warming on denitrification rates and N2O production. Here we used a series of whole core incubation studies to assess the combined impact of warming and OA on estuarine sediment denitrification rates and N2O production. Strong warming (+5 °C over mean in situ conditions) increased N2O production by ~4.2 µmol-N m−2 d−1 and denitrification by ~43 µmol-N m−2 d−1, fuelled by water column nitrate (Dw), but decreased rates of nitrification-coupled denitrification in the sediment (Dn) by ~82 µmol-N m−2 d−1. While Dn was not affected by OA, Dw decreased significantly by 51 µmol-N m−2 d−1 when OA was coupled with warmer temperatures. We estimate that OA may offset the increase in estuarine sediment denitrification and N2O production expected from warming alone by up to 64% and reduce a potential positive climate feedback loop by inhibiting denitrification pathways.

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Impact of anthropogenic global hypoxia on the physiological response of bivalves

Published 15 April 2024 Science Closed
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Dissolved oxygen (DO) is an important parameter that affects the biology, physiology, and immunology of aquatic animals. In recent decades, DO levels in the global oceans have sharply decreased, partly due to an increase in atmospheric carbon dioxide, temperature, and anthropogenic nutrient loads. Although there have been many reports on the effects of hypoxia on the survival, growth, behavior, and immunity of bivalves, this information has not been well organized. Therefore, this article provides a comprehensive review of the effects of hypoxia on bivalves. In general, hypoxia negatively impacts the food consumption rate and assimilation efficiency, as well as increasing respiration rates in many bivalves. As a result, it reduces the energy allocation for bivalve growth, shell formation, and reproduction. In severe cases, prolonged exposure to hypoxia can result in mass mortality in bivalves. Moreover, hypoxia also has adverse effects on the immunity and response of bivalves to predators, including decreased burial depths, sensitivity to predators, impairment of byssus production, and negatively impacts on the integrity, strength, and composition of bivalve shells. The tolerance of bivalves to hypoxia largely depends on size and species, with larger bivalves being more susceptible to hypoxia and intertidal species being relatively more tolerant to hypoxia. The information in this article is very useful for elucidating the current research status of hypoxia on bivalves and determining future research directions.

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Exploring the mechanisms behind swimming performance limits to ocean warming and acidification in the Atlantic king scallop, Pecten maximus

Published 15 April 2024 Science Closed
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Recently, we could show that scallops show limitations of muscular performance like a reduced force under ocean warming and acidification. However, the underlying mechanisms at the cellular level are not completely understood. Metabolomics has become a valuable tool to evaluate the responses of marine organisms to various stressors. In the present study we therefore used a semi-targeted, multi tissue NMR based metabolomic approach to analyze metabolite patterns in the Atlantic king scallop, Pecten maximus, that were long-term acclimated to different end of century conditions of ocean warming (OW), ocean acidification (OA) and their combination (OWA). We investigated tissue specific metabolic profiles and metabolite concentrations in frozen tissues from gills, mantle and phasic and tonic adductor muscle of P. maximus under present conditions using 1H-HR-MAS NMR spectroscopy. A set of 33 metabolites revealed a clear tissue-specific pattern which can be attributed to the individual functions of the respective tissue type. We then evaluated the impact of OW, OA and OWA on the metabolic profiles of the different tissues. OW was the main driver of the changes in metabolites. In particular, energy-related metabolites seem to play an important role in the physiological response of scallops to OW and OWA. In combination with pathway analysis and network exploration we propose a possible correlation between metabolic changes in the adductor muscle and limited swimming performance of P. maximus under future climate. While the metabolic response of the phasic muscle seems to mainly depend on net consumption of energy related metabolites such as ATP and phospho-L-arginine, the tonic muscle seems to rely on metabolizing specific amino acids and beta-oxidation to account for the elevated energetic requirements under ocean warming and acidification.

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Comprehensive assessment of copper’s effect on marine organisms under ocean acidification and warming in the 21st century

Published 15 April 2024 Science Closed
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Highlights

  • The MLR models between pH, temperature and Cu toxicity were developed.
  • The WQC of Cu for 2020, 2099-RCP2.6, 2099-RCP4.5, and 2099-RCP8.5 were derived.
  • Cu in the Ocean of East China poses a moderate ecological risk.
  • Ocean acidification and warming can increase the effects of Cu on marine organisms.
  • Cu’s ecological risk in 2099 under RCP2.6 is significantly lower than that of RCP8.5.

Abstract

Copper (Cu) has sparked widespread global concern as one of the most hazardous metals to aquatic animals. Ocean acidification (OA) and warming (OW) are expected to alter copper’s bioavailability based on pH and temperature-sensitive effects; research on their effects on copper on marine organisms is still in its infancy. Therefore, under representative concentration pathways (RCP) 2.6, 4.5, and 8.5, we used the multiple linear regression-water quality criteria (MLR-WQC) method to assess the effects of OA and OW on the ecological risk posed by copper in the Ocean of East China (OEC), which includes the Bohai Sea, Yellow Sea, and East China Sea. The results showed that there was a positive correlation between temperature and copper toxicity, while there was a negative correlation between pH and copper toxicity. The short-term water quality criteria (WQC) values were 1.53, 1.41, 1.30 and 1.13 μg·L−1, while the long-term WQC values were 0.58, 0.48, 0.40 and 0.29 μg·L−1 for 2020, 2099-RCP2.6, 2099-RCP4.5 and 2099-RCP8.5, respectively. Cu in the OEC poses a moderate ecological risk. Under the current copper exposure situation, strict intervention (RCP2.6) only increases the ecological risk of copper exposure by 20 %, and no intervention (RCP8.5) will increase the ecological risk of copper exposure by nearly double. The results indicate that intervention on carbon emissions can slow down the rate at which OA and OW worsen the damage copper poses to marine creatures. This study can provide valuable information for a comprehensive understanding of the combined impacts of climate change and copper on marine organisms.

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Relationship between the carbonate system and phytoplankton community in the Gulf of Guinea-Africa

Published 12 April 2024 Science Closed
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We carried out measurements of the CO2 system parameters to evaluate the impact of carbonate and nutrients’ chemistry on phytoplankton populations in the Gulf of Guinea (GoG). The seasonal variations of the CO2 system parameters (fCO2, DIC, pH and TA) along with nitrates and phosphates were quantified weekly at surface (between 0 and 5 m depth) (5.57°N – 4.57°W) in the GoG from May to December 2020. Seawater pH varied widely during the study period, ranging between 8.10-8.35 pH units; DIC and TA varied between 1810 and 2094 μmol kg-1, and between 2051 and 2216 μmol-1 respectively. DIC peaks coincided with the high upwelling period (August and September). For phytoplankton, a total of 60 species were found belonging to four taxonomic phyla: Bacillariophyta, Dinophyta, Chlorophyta and Dictyochophyta. The highest number of phytoplanktonic species were recorded for Bacillariophyta phylum with 36 species (60%). The phylum Dinophyta comprised 22 taxa (36%) and Chlorophyta and Dictyochophyta recorded only one species (2%). The highest specific diversities were observed in August and September with 29 and 26 taxa respectively and the lowest was found in October-November (5 taxa) and December (one taxa). Bacillariophyta and Dinophyta appeared throughout the entire study period. The only species for Chlorophyta phylum appeared in June and July and the Dictyochophyta’s one in May, July and August. In general, the physical (SST, SSS) and chemical (TA, DIC, pH) parameters influenced less than 50% of the phytoplankton population in the coastal area of the GoG. Our study shows that Bacillariophyta population grows up when the physicochemical parameters’ variability increase.

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Effects of pH on olfactory behaviours in male shore crabs, Carcinus maenas

Published 11 April 2024 Science Closed
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The effects of climate change are becoming more apparent, predominantly concerning the impacts of ocean acidification on calcifying species. Many marine organisms rely on chemical signals for processes such as foraging for food, predator avoidance, or locating mates. The process of how chemical cues in marine invertebrates function, and how this sensory mode is affected by pH levels, is less researched. We tested the impact of reduced pH (7.6), simulating end-of-the-century predicted average ocean pH, against current oceanic pH conditions (8.2), on the behavioural response of male shore crabs Carcinus maenas to the female sex pheromone bouquet consisting of Uridine–diphosphate (UDP) and Uridine–triphosphate (UTP). While in current pH conditions (8.2), there was a significant increase in sexual interactions in the presence of female pheromone, males showed reduced sexual behaviours at pH 7.6. The crab weight–pH relationship, in which larger individuals respond more intensely sexually in normal pH (8.2), is reversed for both the initial detection and time to locate the cue. These results indicate that lowered pH alters chemical signalling in C. maenas also outside the peak reproductive season, which may need to be taken into account when considering the future management of this globally invasive species.

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Effects of CO2 on the nitrogen isotopic composition of Trichodesmium and Crocosphaera

Published 11 April 2024 Science Closed
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Biological nitrogen (N2) fixation is the main input of fixed nitrogen to ecosystems on Earth. Nitrogen isotope fractionation during this process is a key parameter for understanding the nitrogen cycle, however, relatively little is known about its regulatory mechanisms. Here we examine the effects of varying CO2 concentrations on biomass δ15N signatures of the cyanobacterial diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii. We show that these organisms produce biomass up to ~3 ‰ lower in δ15N under either decreased (~180 µatm) or elevated (~1400 µatm) CO2 concentrations in comparison to modern levels (~380 µatm). Our results pointed towards changes in nitrogenase enzyme efficiency in response to CO2 perturbations impacting isotopic fractionation during N2 fixation and thus the biomass δ15N. This study contributes to an improved interpretation of the observed fluctuations in the δ15N records, and thus the past nitrogen cycle on Earth.

Continue reading ‘Effects of CO2 on the nitrogen isotopic composition of Trichodesmium and Crocosphaera’

Narrowed gene functions and enhanced transposon activity are associated with high tolerance to ocean acidification in a juvenile subarctic crustacean

Published 11 April 2024 Science Closed
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Ocean acidification (OA) threatens marine crustaceans, particularly those at high latitudes where conditions are rapidly changing. Red king crab (RKC) support important fisheries in Alaskan waters. RKC early life stages are sensitive to OA when exposure occurs as embryos and juveniles. However, in a supporting study, RKC were surprisingly tolerant of varying OA conditions (pH 7.5, 7.8, & 8.0) when reared long-term from larval hatching to the first crab stage (C1). Here, we examined gene expression in the C1 juveniles to characterize transcriptional activity of these OA-tolerant crabs. Expression of nearly half of all genes (44%) correlated with OA treatment, suggesting a strong molecular response to OA, contrary to the phenotypic results. Downregulated functions were numerous in response to OA, and included reduced energy production, biosynthesis, immune function, and notably lipid and carbohydrate metabolic processes, which suggest a shift in metabolic strategy to protein catabolism, possibly to reduce CO2 production and facilitate acid/base regulation. Only a handful of functions were enriched in OA-induced genes, which were related to transcription regulation, control of growth and cell death, and signaling activity. Transposon activity was high in OA-reared crab, many of which were upregulated at consistent levels, suggesting that transposon mobilization may be a component of the RKC OA-response system. Genetic composition did not differ among OA treatments indicating that transcriptional differences in OA-reared crab were more likely attributed to phenotypic plasticity than selective mortality. Our results suggest that OA-reared RKC have a narrowed, possibly optimized, set of gene functions that enables OA-tolerance through the early juvenile stage. OA-exposure from hatch may benefit RKC and related species by “hardening” them against OA through physiological reprogramming. Future studies should test OA-hardened crabs in additional challenges, as metabolic and immune limitations may ultimately make them more vulnerable to infection or secondary stressors.

Continue reading ‘Narrowed gene functions and enhanced transposon activity are associated with high tolerance to ocean acidification in a juvenile subarctic crustacean’

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