Posts Tagged 'morphology'

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Nutritional status and shell properties of the scallop Argopecten purpuratus are sensitive to intense upwelling events

Published 8 July 2025 Science Closed
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Highlights

  • The scallop Argopecten purpuratus cope with permanent environmental fluctuations.
  • Upwelling intensity and duration affect its physiological perfomance.
  • Shell organic matrix was adversely affected by intense upwelling events.
  • The nutritional status of the A. purpuratus is modulated by upwelling intensity.
  • A. purpuratus seems to be partially adapted to colder, low pH and hypoxic conditions.

Abstract

Changes in environmental conditions can be particularly stressful for marine biota. However, marine organisms possess a variety of biological mechanisms (e.g., expression of stress proteins, down or up metabolic regulation, among others) that enable them to adapt to such conditions. This will ultimately determine their resilience and adaptive capacity to the natural environmental fluctuations occurring in their habitats, but also to future climate-driven shifts. In Chile, the scallop Argopecten purpuratus inhabits regions under permanent upwelling conditions causing, at different temporal and spatial scales, cooling, low pH and hypoxic conditions of diverse magnitude. In one-year field experiment, we observed that A. purpuratus was, in some occasions, adversely affected by intense upwelling events during the spring season, when the most intense upwelling events were observed, and thus the lowest temperatures, pH and oxygen levels were registered. These effects were more evident in some shell properties, such as the shell organic matrix, a key component of the biomineralization process. Also, no impacts or positive responses (i.e., up-regulation) were observed on parameters associated to their nutritional status (i.e., carbohydrate and protein muscle content), and periostracum thickness suggesting the presence of physiological trade-offs, but also adaptive mechanisms serving to cope with stressful environmental conditions. Ultimately, our findings also raise concerns about the potential consequences of intensified upwelling due to climate change, particularly for the aquaculture sector that relies on this species, since the majority of impacts were observed in individuals of sizes considered attractive to the market.

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Increased temperature and acidification elevate the risk of starvation in American lobster larvae 

Published 4 July 2025 Science Closed
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The geographic range of the American lobster, Homarus americanus, spans a steep thermal gradient along the coastal Northwest Atlantic. As CO2 emissions increase globally, this range is rapidly warming and acidifying. Larval H. americanus hatch with a finite amount of maternally sourced lipid stores in their yolk sac, which provide an energetic buffer during the intermediate period between hatch and first feed. This study examines the response of newly-hatched, unfed H. americanus larvae to the combined effects of elevated pCO2 and temperature. Using a space-for-time approach, we compared larvae of two distinct sub-populations from thermally contrasting regions: Rhode Island, at the warmer, southern limit of the species range, and Midcoast, Maine, a cooler northern region. Average larval initial post-hatch weight was similar across regions and variability therein could be explained by maternal effects. Under 6 days of starvation, larvae from the two regions lost ∼14% of their initial dry weight and 25% of their Carbon weight. Still, end-century elevated temperature or acidification did not substantially alter those rates for larvae from either region. However, under an identical range of conditions over the 6-day experiment, larvae from the warmer regime maintained relatively stable oxygen consumption rates, while those from the cooler regime started 50% higher, then dropped by 80% within 2 days. If depressed metabolic functioning translates to reduced feeding efficiency for cool regime larvae, our findings suggest that subpopulations in the southern edge of the species range have a relative advantage in food-scarce environments under these conditions, adding to previous evidence for countergradient variation in this species. Further analysis of total fatty acid losses conducted on Midcoast larvae suggested starved larvae exposed to elevated temperature (19°C) experienced considerably greater losses of key lipid groups than larvae under ambient conditions (16°C, 400 ppm), particularly within the first 2 days of exposure. Our results highlight the short time frames over which ocean warming can accelerate the depletion of energy stores and make larvae more vulnerable to starvation.

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Brachiopods and forams reduced calcification costs through morphological simplification during mass extinction events

Published 3 July 2025 Science Closed
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Environmental stressors have exacerbated the collapse of marine ecosystems during mass extinctions. However, the survival strategies of marine species during mass extinctions remain unclear. Here, we investigated morphological evolution of brachiopods across the Permian–Triassic mass extinction (PTME) using a database of 3,225 specimens representing 1,061 species and foraminifera across the PTME and early Toarcian oceanic anoxic event (T-OAE) using a database of 757 specimens representing 12 species. We found a significant reduction in the number and proportion (plicae length/shell length) of shell plicae of brachiopods (36.4% and 60.0%, respectively) across the PTME and a significant decrease in the shell thickness of foraminifera (18.9% and 42.4% across the PTME and 36.9–61.8% across the T-OAE). We calculated that these adaptive strategies could reduce the energetic costs of calcification by more than half for brachiopods across the PTME, and by ~20–62% for foraminifera across the PTME and T-OAE, to compensate for the elevated cost of calcification due to environmental and ecological pressures. We propose that simplification of morphological features, such as reduced shell ornamentation and shell thinning, serves as a potential economic strategy for calcifying organisms to cope with extinction events by reducing energy demands, but further studies with a broader range of taxa and extinction events are needed to confirm the generality of this bioenergetic strategy.

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Impacts of ocean acidification and altered prey fatty acids on the early development of northern rock sole (Lepidopsetta polyxystra) larvae

Published 3 July 2025 Science Closed
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Highlights

  • Carbon dioxide (CO2) and dietary fatty acids (FAs) had stage-specific effects on northern rock sole larvae.
  • After 2-weeks of feeding, larvae had faster growth under elevated CO2 conditions.
  • After 5-weeks of feeding, larvae had higher lipid storage when fed a diet with balanced-essential FAs.

Abstract

Ocean acidification (OA) is predicted to affect the physiological rates of larval fish and invertebrates and is also expected to significantly impact marine fisheries through alteration of food webs. We examined whether mortality rates, body size, and condition of first-feeding larval northern rock sole, Lepidopsetta polyxystra, were synergistically influenced by prey quality (essential fatty acids, EFAs) and high carbon dioxide (CO2) exposure. Larvae were exposed to ambient and high CO2 levels (∼ 330 vs. 1020 μatm) and were fed diets with balanced or unbalanced EFA ratios for 7 weeks immediately following hatch. After 2 weeks, significant effects from CO2 and diet were observed, with the largest larvae occurring in the high CO2 exposure group that received a balanced EFA diet. After 5 weeks of exposure, the effects of elevated CO2 had a diminished impact on larval size, but larvae reared on the balanced EFA diet maintained higher lipid-based condition metrics than those fed an unbalanced EFA diet. Survival was variable across replicate tanks and not significantly different between treatments. This study suggests that L. polyxystra larvae are most vulnerable to OA and food web change at different points in their development. Further understanding of these ecosystem effects will be required to predict the impacts of OA on northern rock sole fisheries.

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Ocean acidity extremes retard shell formation of bivalve larvae: insights from transcriptomics and lipidomics

Published 2 July 2025 Science Closed
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Highlights

  • Effects of ocean acidity extremes (OAX) on early development of clams were assessed.
  • OAX retarded shell formation of clam larvae.
  • Reduced Ca2+ uptake and HCO3− production led to larval developmental retardation.
  • OAX decreased cell membrane fluidity, limiting the uptake of calcification substrates.
  • Larval shell formation under OAX was inhibited by depletion of energy reserves.

Abstract

In view of climate change and human activities, ocean acidity extreme (OAX) events have been increasingly reported worldwide over the last decades, which possibly retard the growth and development of marine organisms, particularly at their early life-history stages (e.g., embryos or larvae). Thus, understanding whether they can adjust to the sudden increase in seawater acidity has drawn growing attention. Using a commercially and ecologically important bivalve species (Ruditapes philippinarum) with a widespread distribution in the world, we assessed the impact of OAX on its embryonic and larval development as well as expressions of functional genes and lipids to indicate physiological and cellular performance. We found that embryonic development and larval shell formation were inhibited by OAX mainly due to the downregulation of key genes responsible for the uptake of calcium ions from ambient seawater (e.g., NCX, VGCC and SERCA) and the reduced production of bicarbonate ions through the catalytic action of carbonic anhydrase. In addition, a major remodelling in membrane lipids (e.g., PC, PE, PG, PI and PS) indicated that OAX impacted the fluidity and stability of cell membrane, hindering the uptake of calcification substrates. The depletion in energy reserves, such as triacylglycerol, can also account for the impairment in larval shell formation under OAX conditions. By integrating transcriptomics and lipidomics, our findings illustrate a novel molecular mechanism underlying the detrimental effect of OAX on larval development and hence population maintenance of marine organisms, which can have profound implications for sustaining ecosystem stability and aquaculture management.

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Assessing pteropod shell dissolution to advance ocean monitoring techniques: a methods comparison of SEM, CT, and light microscopy

Published 30 June 2025 Science Closed
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Pteropods are marine planktonic snails that are used as bioindicators of ocean acidification due to their thin, aragonitic shells, and ubiquity throughout the world’s oceans; their responses include decreased size, reduced shell thickness, and increased shell dissolution. Shell dissolution has been measured with a variety of metrics involving light microscopy, scanning electron microscopy (SEM), and computed tomography (CT). While CT and SEM metrics offer high resolution imaging, these analyses are cost- and time-intensive relative to light microscopy analysis. This research compares light microscopy, CT, and SEM shell dissolution metrics across three pteropod species: Limacina helicina, Limacina retroversa, and Heliconoides inflatus. Sourced from multiple localities, these specimens lived in tropical to subpolar environments and were exposed to varying aragonite saturations states due to oceanographic differences in these environments. Specimens were evaluated with light microscopy for the Limacina Dissolution Index (LDX), with SEM for percent of pristine shell coverage and maximum dissolution type, and with CT for whole-shell thickness. LDX and the percentage of pristine shell determined via SEM were highly correlated in all three species’ datasets. For L. retroversa, LDX was also significantly correlated to SEM maximum dissolution type. Although the genera Heliconoides and Limacina have different shell microstructures, the relationship between LDX and SEM dissolution did not vary by species. The CT metric for shell thickness was not significantly correlated to any other dissolution metrics for any species. However, severely dissolved areas apparent in SEM were visually discernible in CT thickness heatmaps. While CT may not detect minor shell dissolution, previous studies have used CT to detect reduced calcification in response to ocean acidification. SEM is ideal for detecting the onset of dissolution, but SEMing large numbers of specimens may not be practical due to monetary and time constraints. LDX, on the other hand, is a fast and cost-effective metric that is strongly correlated with SEM metrics, regardless of the oceanographic conditions that those species experienced. These results suggest that an efficient ocean acidification monitoring strategy is to evaluate all pteropod specimens via LDX and to then SEM a subset of those specimens.

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Combined physiological effects of differentially charged nanoplastics and ocean acidification on the mussel Mytilus coruscus

Published 26 June 2025 Science Closed
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Highlights

  • OA enhances the effect of P-NPs on mussels.
  • The effect of P-NPs on oxidative stress of mussels was more significant.
  • OA changes the effect of differentially charge nanoplastics on energy metabolism.
  • OA may affect the behavior and toxicity of NPs by altering its charge distribution.

Abstract

In the context of ocean acidification (OA) in the near future, along with the continuous production of nanoplastics (NPs) with different charges in the ocean, it is critical to investigate their combined effects on marine life and ecosystem stability. Thus, this study assessed the joint effects of NPs with different charges and OA on Mytilus coruscus by analyzing antioxidant stress, energy metabolism, condition index, and shell resistance. Results indicated that positively charged NPs (P-NPs) significantly elevated ROS levels, MDA content, and the activities of GPX and CAT, with more pronounced effects under OA. NPs with different charges have varying effects on energy metabolism enzyme activity, and OA further influences these disparities. Overall, P-NPs had a more detrimental impact on mussels, an effect that was further intensified by OA. Low pH alters the surface charge distribution of NPs, enhancing their binding to biomolecules and potentially exacerbating physiological effects on mussels by altering NPs’ aggregation behavior. This study provides insights into the combined toxic effects of NPs with different charges and OA on mussels, offering a reference for evaluating the environmental risks of OA and charged NPs in marine ecosystems.

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Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply

Published 26 June 2025 Science Closed
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Soft-sediment habitats are crucial for marine coastal ecosystems, supporting diverse biodiversity both above and below the sediment. Ocean acidification, driven by rising CO2 and nutrient influx, enhances heterotrophic metabolism, raising CO2 levels and lowering pH. These alterations complicate the dynamics of tidal flat, emphasizing the need for further research into their impact on biodiversity. Within these ecosystems, deposit- and suspension-feeding bivalves play crucial roles. Tagelus dombeii, a bivalve mollusc found in soft sediments, exhibits burrowing behavior linked to food supply and is of significant commercial value in southern Chile. This study assessed the response capacity of T. dombeii to key stressors associated with global ocean change, such as ocean acidification and food availability. Our results revealed significant differences in pH levels between the water column and pore water from the sediment in experimental mesocosms. T. dombeii was affected by ocean acidification and food availability in terms of its morphological traits (i.e. length, width, height and growth rate), while oxygen consumption was influenced only by the interaction between acidification and food supply. Notably, heart rate remained constant but increased when food supply was low. Our study suggests that T. dombeii exhibits partial tolerance to variations in seawater pH and carbonate chemistry, possibly due to its natural exposure to acidic pore water, but it is sensitive to food availability. These plastic physiological responses suggest that T. dombeii may be less vulnerable to future global change scenarios, demonstrating potential resilience and ecological success in its natural habitat.

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Short and long-term exposure to ocean acidification in limpets from the Castello Aragonese vent systems (Ischia Island, Italy)

Published 12 June 2025 Science Closed
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Highlights

  • First investigation limpet populations collected from the naturally acidified site.
  • Increased dimension and energy endpoints in Patella caerulea from very low pH (<7.4).
  • Induction of antioxidant systems and neurotoxicity in Patella rustica exposed to OA.
  • Transplant of Patella caerulea activated oxidative stress and neurotoxicity endpoints.

Abstract

Ocean acidification (OA) is reported to entail a detrimental impact on calcifying organisms. Nevertheless, patellid limpets – P. caerulea, P. rustica, and P. ulyssiponensis – are able to persist in extremely low pH conditions inside the Castello Aragonese CO2 vent systems (Ischia Island), suggesting that they may have developed tolerance to OA, through plasticity and/or adaptive mechanisms. The aim of this study is to evaluate the long-term strategies adopted by limpets that spent their entire life cycle in naturally acidified conditions and the short-term ones induced by a 30-day in situ transplant experiment.

Regarding native limpet populations, P. caerulea exhibited increasing size and higher energy resources in the extremely acidified site, potentially related to different food availability or to reduction in competition and/or predatory pressure; furthermore, no effects on oxidative stress, biomineralization and neurotoxicity occurred. Similarly, P. ulyssiponensis didn’t exhibit any significant effects among different pH conditions regarding biochemical endpoints. Conversely, P. rustica displayed a significant modulation of almost all biochemical parameters, possibly due to its different position on the rocky shore. The short-term exposure of P. caerulea produced a decrease in protein content and an increase in glycogen content in the extreme acidified site, with an induction of superoxide dismutase and glutathione-S-transferases activities in the intermediate pH site.

Overall, our study revealed that different species of the same genus may have developed distinct responses to OA and suggested different mechanisms to cope with short and long-term exposure to low pH conditions.

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Population and maternal variation in the sensitivity of Dungeness crab Metacarcinus magister zoeae to elevated CO2

Published 10 June 2025 Science Closed
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The response of marine organisms to ocean acidification depends on their adaptive capacity, which can be partially understood by evaluating the amount of existing variability in CO2 sensitivity within a species. The process of local adaptation is a mechanism that can drive variability in CO2 sensitivity. In this study, we measured the survival and molt rate of Dungeness crab Metacarcinus magister zoeae that were produced by gravid crabs collected from 3 locations in waters off of Washington State, USA, and reared in a common laboratory in ambient, medium, and high CO2 treatments. The 3 locations from which crabs were collected have different carbonate chemistry dynamics, and Dungeness crabs in these locations are to some extent genetically distinct. We hypothesized that these conditions may favor local adaptation. We did not find evidence of local adaptation, but did see different levels of CO2 sensitivity associated with the mother. This variation in CO2 sensitivity suggests an adaptive capacity that is likely to influence Dungeness crab response to future acidification.

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Effects of ocean warming and acidification on the embryonic development of Doryteuthis opalescens and Doryteuthis pealeii

Published 9 June 2025 Science Closed
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Projected increases in ocean temperature and partial pressure of carbon dioxide (pCO2) due to anthropogenic carbon emissions are expected to significantly alter coastal marine ecosystems, particularly within the Southern California Bight and Northwest Atlantic Ecoregion. These changes may disrupt food web stability through alterations in abiotic conditions. To assess the impacts of elevated temperature and pCO2 on embryonic development in the superorder Decapodiformes, I investigated two mid-trophic squid species, Doryteuthis opalescens and Doryteuthis pealeii, during their paralarval stage. Specifically, I examined metabolic and morphological responses in squid reared in four seawater treatments: combinations of present-day and projected levels of temperature and pCO2 by the end of the century. The results revealed species-specific responses. D. opalescens paralarvae exhibited generally negative responses, including reduced morphological development, under elevated temperature and pCO2 conditions. In contrast, D. pealeii paralarvae demonstrated positive responses, with increased morphological dimensions under the same conditions. Additionally, D. pealeii paralarvae showed elevated O2 consumption rates, while D. opalescens paralarvae exhibited a more subdued metabolic response to temperature increases. These findings highlight significant interspecific variability in responses to future ocean conditions, despite the similarity in life history traits between the two species. This study underscores the complexity of climate change impacts on Decapodiformes and emphasizes the necessity of species-specific assessments to predict ecological consequences for marine organisms.

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Exposure of larval pinto abalone to ocean acidification and warming negatively impacts survival, settlement, and size

Published 13 May 2025 Science Closed
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Pinto abalone (Haliotis kamtschatkana), the only abalone species native to Washington, declined by 97% in the state from 1992 to 2017. Their decline is a loss for indigenous tribes, recreational divers, and the health of subtidal rocky reefs and kelp beds. Current restoration actions are facing threats of ocean acidification and warming in the northeast Pacific. This research aims to deepen our understanding of the tolerance and physiological flexibility of early life history stages of pinto abalone and inform hatchery practices under future climate change scenarios. We conducted an experiment to test how seawater pH and temperature stress impact abalone larvae. We exposed abalone post-fertilization to elevated temperature and reduced seawater pH for ten days spanning their larval development period: (1) 7.95pH/14°C (ambient), (2) 7.60pH/14°C, (3) 7.95pH/18°C, and (4) 7.60pH/18°C. Abalone in the ambient treatment had the best survival, those in the 7.60pH/18°C treatment had the worst survival, and those in the two single-stressor treatments had survival in between. Among the surviving larvae, pH was the dominant stressor influencing settlement success, with higher settlement rates under ambient pH treatments at both temperatures. pH also had a stronger effect than temperature on shell length. The information gleaned from this study is essential for optimizing future restoration aquaculture for pinto abalone and determining their ideal habitat and potential geographic range.

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Increasing acidification does not affect sexual reproduction of a solitary zooxanthellate coral transplanted at a carbon dioxide vent

Published 8 May 2025 Science Closed
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The absorption of atmospheric carbon dioxide is causing significant changes to the carbonate chemistry of the ocean, in a phenomenon called ocean acidification. The latter makes it potentially more difficult for marine calcifiers like corals, to build their calcium carbonate structures, thus affecting their ability to survive and reproduce. Research on how ocean acidification impacts coral sexual reproduction has focused on tropical species investigated under controlled conditions in aquaria, lacking insights into the intricate natural environment. Here we show that the sexual reproduction of the zooxanthellate solitary scleractinian Balanophyllia europaea transplanted at a CO2 vent off the Island of Panarea (Tyrrhenian Sea, Italy) for up to 5 months is unaffected by decreasing pH (pH range 8.1–7.4). These findings reinforce earlier evidence, suggesting that zooxanthellate corals may exhibit a certain degree of short-term resilience to ocean acidification. However, the interplay between ocean acidification and additional environmental stressors, including warming, will ultimately define the boundaries that distinguish winners and losers amid swift climatic changes.

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A widely distributed clam, Chama macerophylla, exhibits mixed responses to single and combined warming and acidification stress

Published 7 May 2025 Science Closed
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Bivalves enhance microhabitat complexity and improve water clarity in coastal ecosystems. Ocean warming (OW) and acidification (OA), pose a significant threat to bivalves in shallow continental shelf environments where stressors can be amplified and uncoupled. This study investigated global change effects on Chama macerophylla, a widespread clam in the Gulf of Mexico. Laboratory experiments assessed physiology and shell mineralogy of C. macerophylla exposed to different levels of OW, OA, and combined stressors (OWA). Temperature and carbonate chemistry from collection sites confirm ambient (control) treatments used in experiments were commonly observed in the field. Clam oxygen consumption increased with OW and, initially, with OA. After 30 days, clams within moderate and extreme OA lowered consumption. In contrast, clam oxygen consumption declined in OWA treatments. Net calcification was only affected by OA with higher calcification in the extreme treatment than in moderate. Meat weight relative to shell weight (condition) was negatively affected by OW in the extreme treatment. Shell accretion, clearance rates, and mineralogy were unaffected by OW, OA, and OWA. This is the first report of a bimineralic shell for this species. Results highlight resilience of clam survivorship to stressors. OW appears to increase metabolism and drive declines in clam condition (meat: shell weight). OWA may have a greater impact on C. macerophylla than single stressors, particularly if reduced oxygen consumption is sustained. This research underscores the need to understand long-term stress on bivalves. Future research should examine both size-age relationships with global stressors and the role of acclimation to prolonged stress.

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Pteropods as early-warning indicators of ocean acidification

Published 6 May 2025 Science Closed
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Aragonite undersaturation (Ωar < 1) events are projected to rapidly increase in frequency and duration in the Antarctic Weddell Sea by 2050. Thecosome pteropods (pelagic snails) are bioindicators of ocean acidification (OA) because their aragonite shell dissolves easily at low Ωar saturation states. Here, we describe the shell dissolution state of the pteropod Limacina helicina antarctica in relation to the water column Ωar in the southern Weddell Sea during austral summer 2018 as benchmark for future monitoring of ongoing OA. Ωar depth profiles at the sampling sites were consistently close to or in the range of threshold levels (Ωar ~ 1.1–1.3) for pteropod shell dissolution. Pteropods contributed up to 69% of total mesozooplankton biomass, and their distribution correlated positively with Ωar and chlorophyll a concentration. When analyzed with scanning electron microscopy, 78% of the investigated shells exhibited dissolution, and 50–69% showed the more severe Type II dissolution exceeding current projections of pteropod shell dissolution for the Southern Ocean. But importantly, in our study, only two specimens had the most severe Type III dissolution. Dissolution often co-occurred with and occurred in scratch marks of unclear origin supporting notions that an intact periostracum protects the shell from dissolution. Where dissolution occurred in the absence of scratches or absence of evidence of periostracum breaches, microscale/nanoscale breaches may have been an important pathway for dissolution commencement supporting recent findings of a reduction of the organic shell content caused by low Ωar/low pH. The dissolution benchmark we provide here allows future application of pteropods as early-warning indicators of presumably progressing OA in the Weddell Sea.

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Low-pH conditions drive transient changes in shell calcification and the microbiome in a pH-resistant strain of the the Pacific oyster Magallana gigas

Published 29 April 2025 Science Closed
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The study explores the effects of elevated pCO2 on shell calcification, microbiome composition, and gene expression in a strain of Pacific oyster (Magallana gigas) selectively bred for low-pH resistance. Juvenile oysters reared under low-pH conditions exhibited increased shell mass compared to the control population by 51 days post-fertilization, despite high variance in shell size at earlier stages. Microbiome analyses revealed significant shifts in community composition under low-pH conditions, particularly in bacterial taxa involved in CO2 production and biogeochemical cycling, which could influence carbonate chemistry within oyster tissues. Gene expression profiling demonstrates differential regulation of genes related to biomineralization, immunity, and microbial interactions under low-pH conditions. For example, multiple carbonic anhydrases exhibited treatment-specific expression patterns, suggesting a role in adapting to low-pH environments. Observed changes in immune-related genes imply a relaxation of immune responses, potentially reflecting resource reallocation toward calcification processes. These results collectively support the “dysbiosis hypothesis,” where oysters adapt to environmental stress by modulating their microbiomes and gene expression. Future studies should investigate whether these responses are consistent across oyster strains and environmental conditions, providing insights into the resilience of aquaculture species to ocean acidification.

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A simple CO2 enrichment incubator for investigating physiological responses of harmful algae to ocean acidification

Published 23 April 2025 Science Closed
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A CO2 manipulation incubation system using off-the-shelf components was developed to study the effects of ocean acidification (OA) on marine microalgae. The system successfully monitored CO2 concentrations in real time at the desired levels. The incubation experiment was based on the IPCC’s CMIP6 worst-case scenario (SSP5-8.5), with elevated CO2 concentrations of up to 1000 ppm. Under these conditions, exposure to 1000 ppm CO2 significantly increased growth rate, cell diameter, and biovolume of harmful microalgae, Alexandrium tamiyavanichii. These effects were more pronounced, highlighting the potential for ocean acidification to exacerbate harmful algal blooms. The study also emphasized the importance of accounting for light attenuation in the incubation setup, revealing a 20% loss in light within culture bottles due to uneven light distribution. Correcting light intensity variations caused by the materials of the culture vessels was essential for unbiased growth assessments.

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Record of foraminifera test composition throughout the Phanerozoic

Published 17 April 2025 Science Closed
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Marine calcifiers produce calcareous structures (e.g. shells, skeletons or tests) and are therefore sensitive to ocean chemistry. Nevertheless, the long-term evolutionary consequences of marine carbonate changes are not well understood. This article compares calcareous and non-calcareous responses to ocean chemistry changes throughout the Phanerozoic Eon (541 million years ago to present). To accomplish this, we calculated proportional wall-type diversity, origination rates and extinction rates for 2282 benthic foraminiferal genera. Calcareous origination and extinction rates fluctuated throughout the Palaeozoic Era (541–251.9 million years ago), but during the Mesozoic Era (251.9–66 million years ago), calcareous origination and extinction rates stabilized following the evolution of pelagic calcifiers. Despite variations in Cenozoic Era (66–0 million years ago) foraminifera diversity, calcareous wall types maintained around 77% proportional diversity. Although calcareous wall-type extinction rates decline during the Mesozoic and Cenozoic, Phanerozoic foraminifera wall-type changes during individual events are largely contingent upon contemporaneous conditions rather than overarching trends. Of the Big Five mass extinction events, calcareous wall-type proportions only decreased at the end-Permian (73% to 26% diversity) and end-Triassic (56% to 50% diversity). These results suggest long-term ocean chemistry changes were not the main driver of foraminiferal wall-type diversity through time.

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Calcification of planktonic foraminifer Neogloboquadrina dutertrei and its indicative significance for ocean acidification

Published 16 April 2025 Science Closed
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Planktonic foraminifera are widespread calcifying protozoa and represent a primary source of marine biogenic calcium carbonate. Elucidating the mechanisms underlying the calcification processes of planktonic foraminifera holds significant importance for understanding the marine biological pump and carbon cycling.

The present study investigated the controlling mechanisms of calcification in modern planktonic foraminifer Neogloboquadrina dutertrei by analyzing the foraminiferal shell weight data from 92 sets of surface sediments from different ocean areas, including the eastern tropical Indian, the western tropical Pacific, the eastern tropical Pacific, and the western tropical Atlantic. First, this study reveals that deep-ocean carbonate dissolution, which is related to deep-ocean carbonate ion saturation state (Δ[CO32-]), is the dominant factor influencing the shell weight of N. dutertrei in surface sediments. Then, by correcting the dissolution effect on the shell weight of N. dutertrei, we estimated the initial shell weight from which to assess secular changes in the degree of calcification of N. dutertrei. The initial shell weight results suggest that the calcification of N.dutertrei is mainly controlled by seawater carbonate system parameters such as pH, carbonate ion concentration ([CO32-]), and carbon dioxide concentration (pCO2). Calcification of N. dutertrei would decrease with ocean acidification.

Furthermore, we reconstructed initial shell weight of N.dutertrei at sites KX97322-4 and U1490 in the western tropical Pacific to evaluate the response of N. dutertrei calcification to climate changes over glacial-interglacial time scales. Calcification of N. dutertrei in the western tropical Pacific has increased during glacial periods in response to lower atmospheric pCO2 since 800 ka, confirming the dominant influence of ocean acidification on N. dutertrei calcification. We suggest that the shell weight of specific planktonic foraminiferal species may serve as a potential proxy for past seawater carbonate system reconstructions.

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Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum

Published 15 April 2025 Science Closed
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Coccoliths are widely present in marine sediments of the South China Sea and closely associated with paleoenvironmental changes. This study investigates the morphological variations and driving factors of coccoliths since the Last Glacial Maximum(LGM) by analyzing the morphology and related indicators of Noelaerhabdaceae coccoliths in sediment samples from core MD18-3569 (0.01~12.41 m; 0.69~26.58 ka) in the northeastern South China Sea(22°09.30’N, 119°49.24’E at water depth 1320 m), and a total of 155 samples were collected, with a sampling resolution of approximately 167 years. Morphological attributes such as coccolith length, thickness, area, and mass were obtained through microscopic measurements and computational formulas. Coccolith morphological constants were used to evaluate preservation conditions. Based on these data, morphological divergence index and calcification index were calculated. Using the PyCO2SYS model, ocean carbonate system parameters were reconstructed to explore their impact on coccolith morphology.

The results show that coccolith length ranged from 2.69 μm to 3.86 μm(mean: 3.20 μm) since the LGM, with significant variability but no clear trend. Thickness ranged from 0.07 μm to 0.17 μm(mean: 0.13 μm) and exhibited a decreasing trend since the LGM. Coccolith mass varied between 2.31 pg and 9.02 pg(mean: 5.61 pg), also showing a decreasing trend since the LGM. Coccolith morphological constants indicate good preservation and high data reliability. Morphological divergence index results suggest a decline in coccolith size diversity, reflecting reduced seasonal variation and regional productivity. Calcification intensity metrics indicate a weakening of calcification since the LGM.

By comparing temperature, salinity, and ocean carbonate system parameters, the study identifies rising atmospheric CO2 concentrations and resultant ocean acidification as the primary factors contributing to reduced coccolith calcification. The impacts of temperature and salinity were relatively minor. These findings demonstrate the complex response of Noelaerhabdaceae coccoliths to environmental changes and highlight the significant roles of regional climate variations and carbonate system evolution in shaping coccolith morphology.

Continue reading ‘Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum’

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