Coral reefs are vital marine ecosystems that harbor a significant proportion of the ocean’s biodiversity. However, these ecosystems are increasingly threatened by anthropogenic activities, particularly the emission of greenhouse gases leading to climate change and ocean acidification. Ocean acidification refers to the reduction in pH of marine waters due to the absorption of CO₂ from the atmosphere, forming carbonic acid (H₂CO₃), which dissociates into bicarbonate (HCO₃−) and hydrogen ions (H+), thus lowering pH. This sequence of reactions leads to an increase in hydrogen ion concentration, causing a decrease in pH. The reduction in carbonate ions (CO₃2−) is particularly detrimental to marine calcifiers, including corals, which rely on carbonate for the formation of their calcium carbonate (CaCO₃) skeletons. Coral reefs are constructed by the deposition of CaCO₃ by coral polyps. Zooxanthellae, symbiotic algae living within coral tissues, provide essential nutrients through photosynthesis, facilitating calcification. Acidification disrupts this symbiotic relationship by impairing photosynthetic efficiency and reducing the availability of carbonate ions necessary for skeletal growth. As ocean acidification progresses, the concentration of carbonate ions diminishes, making it energetically more challenging for corals to secrete their skeletons, thereby slowing growth rates and compromising structural integrity. Coral bleaching occurs when corals, under stress, expel their zooxanthellae, leading to a loss of pigmentation and a decline in energy reserves. Stressors include elevated sea temperatures, pollution, and acidification. The loss of zooxanthellae not only deprives corals of their primary food source but also disrupts calcification processes. Thermal stress is a predominant factor in coral bleaching. Elevated sea temperatures can destabilize the photosynthetic machinery of zooxanthellae, producing reactive oxygen species (ROS) that damage both the algae and coral tissues. Prolonged exposure to high temperatures exacerbates acidification effects, intensifying bleaching events. The decline in coral health due to bleaching and acidification has profound ecological impacts, including the loss of habitat for numerous marine species, reduced biodiversity, and compromised fisheries. Socioeconomically, coral reef degradation affects tourism, coastal protection, and the livelihoods of communities dependent on reef resources. Reduction of CO₂ emissions through global policy agreements and renewable energy adoption. Local conservation efforts, such as marine protected areas (MPAs) have the potentials to enhance reef resilience. Conservation efforts may be complemented by research into coral species and strains with higher tolerance to acidification and thermal stress, potentially involving selective breeding and genetic modification. Marine water acidification and coral bleaching are intricately linked phenomena driven by anthropogenic climate change. The decline of coral reefs signals a broader environmental crisis that necessitates urgent scientific, policy, and community responses to mitigate adverse effects and foster adaptive resilience in marine ecosystems.
Continue reading ‘Marine water acidification and coral bleaching’Posts Tagged 'protists'
Marine water acidification and coral bleaching
Published 10 December 2024 Science ClosedTags: biological response, BRcommunity, corals, mitigation, protists, review
Chemical interactions between kelp Macrocystis pyrifera and symbiotic bacteria under elevated CO2 condition
Published 26 November 2024 Science ClosedTags: algae, biological response, community composition, molecular biology, otherprocess, physiology, prokaryotes, protists, reproduction
Kelps are pivotal to temperate coastal ecosystems, providing essential habitat and nutrients for diverse marine life, and significantly enhancing local biodiversity. The impacts of elevated CO2 levels on kelps may induce far-reaching effects throughout the marine food web, with potential consequences for biodiversity and ecosystem functions. This study considers the kelp Macrocystis pyrifera and its symbiotic microorganisms as a holistic functional unit (holobiont) to examine their collective response to heightened CO2 levels. Over a 4 month cultivation from the fertilization of M. pyrifera gametes to the development of juvenile sporophytes, our findings reveal that elevated CO2 levels influence the structure of the M. pyrifera symbiotic microbiome, alter metabolic profiles, and reshape microbe-metabolite interactions using 16S rRNA amplicon sequencing and liquid chromatography coupled to mass spectrometry analysis. Notably, Dinoroseobacter, Sulfitobacter, Methylotenera, Hyphomonas, Milano-WF1B-44 and Methylophaga were selected as microbiome biomarkers, which showed significant increases in comparative abundance with elevated CO2 levels. Stress-response molecules including fatty-acid metabolites, oxylipins, and hormone-like compounds such as methyl jasmonate and prostaglandin F2a emerged as critical metabolomic indicators. We propose that elevated CO2 puts certain stress on the M. pyrifera holobiont, prompting the release of these stress-response molecules. Moreover, these molecules may aid the kelp’s adaptation by modulating the microbial community structure, particularly influencing potential pathogenic bacteria, to cope with environmental change. These results will enrich the baseline data related to the chemical interactions between the microbiota and M. pyrifera and provide clues for predicting the resilience of kelps to future climate change.
Continue reading ‘Chemical interactions between kelp Macrocystis pyrifera and symbiotic bacteria under elevated CO2 condition’Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature
Published 25 November 2024 Science ClosedTags: biological response, BRcommunity, corals, laboratory, molecular biology, mortality, multiple factors, North Pacific, photosynthesis, physiology, primary production, protists, reproduction, respiration, temperature
Climate change destabilizes the symbiosis between corals and Symbiodiniaceae. The effects of ocean acidification and warming on critical aspects of coral survical such as symbiotic interactions (i.e., carbon and nitrogen assimilation and exchange) during the planula larval stage remain understudied. By combining physiological and stable isotope techniques, here we show that photosynthesis and carbon and nitrogen assimilation (H13CO3− and 15NH4+) in Pocillopora damicornis coral larvae is enhanced under acidification (1000 µatm) and elevated temperature (32 °C). Larvae maintain high survival and settlement rates under these treatment conditions with no observed decline in symbiont densities or signs of bleaching. Acidification and elevated temperature both enhance the net and gross photosynthesis of Symbiodiniaceae. This enhances light respiration and elevates C:N ratios within the holobiont. The increased carbon availability is primarily reflected in the 13C enrichment of the host, indicating a greater contribution of the algal symbionts to the host metabolism. We propose that this enhanced mutualistic symbiotic nutrient cycling may bolster coral larvae’s resistance to future ocean conditions. This research broadens our understanding of the early life stages of corals by emphasizing the significance of symbiotic interactions beyond those of adult corals.
Continue reading ‘Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature’Ocean acidification does not prolong recovery of coral holobionts from natural thermal stress in two consecutive years
Published 24 September 2024 Science ClosedTags: adaptation, biological response, BRcommunity, calcification, corals, laboratory, mortality, multiple factors, North Pacific, nutrients, otherprocess, physiology, protists, zooplankton
Under predicted future ocean conditions, corals will experience frequent and intense thermal stress events while simultaneously being exposed to chronic ocean acidification. Yet, some corals will likely be more resistant and/or resilient to these predicted conditions than others and may be critical to reef persistence in the future. Following natural thermal stress in two consecutive years (2014 and 2015), we evaluated the effects of feeding and simulated ocean acidification on the physiological recovery of Montipora capitata and Porites compressa sourced from Kāneʻohe Bay and Waimānalo Bay, Hawaiʻi. Following the 2014 thermal stress event, simulated ocean acidification did not slow recovery of the holobiont and feeding enhanced recovery. However, feeding did not decrease susceptibility to the 2015 thermal stress event, and simulated ocean acidification did not increase susceptibility. Recovery strategies employed between species and between sites clearly differed, highlighting that coral reef restoration and management should consider species-level and site-specific vulnerabilities. Overall, our findings call attention to the immediate threat which ocean warming presents, the lack of additional stress to the holobiont from ocean acidification, the importance of heterotrophy in coral resilience, and the potential significance of additional local biotic stressors (i.e., predator outbreaks) for coral resiliency under annual thermal stress.
Continue reading ‘Ocean acidification does not prolong recovery of coral holobionts from natural thermal stress in two consecutive years’Why Amphistegina lobifera, a tropical benthic foraminiferal species, is thriving at temperate latitudes in the Mediterranean Sea
Published 17 September 2024 Science ClosedTags: biological response, Mediterranean, physiology, phytoplankton, protists, review
Amphistegina lobifera Larsen is a relatively large (adult diameter ∼1–3 mm), robust, diatom-symbiont-bearing benthic foraminiferal species that thrives in clear, nutrient-poor coastal waters throughout much of the subtropical/tropical Indo-Pacific. Studies in the late 19th to mid-20th century noted the predominance of the shells of Amphistegina and Calcarina in Holocene reef sediments, enhanced by hydrodynamic sorting and by the resistance of these shells to abrasion. Having migrated through the Suez Canal at least 60–80 years before present, A. lobifera populations have proliferated in the eastern Mediterranean Sea and have expanded their range westward. As Mediterranean waters warm, these foraminifers are thriving in oligotrophic, shallow-water habitats, and have produced shell accumulations of a half meter or more in some areas. While the success of A. lobifera has raised concerns about its proliferation as an invasive species, assessments of foraminiferal assemblages along nutrient gradients have shown dominance only distant from nutrient sources, whether natural or anthropogenic. The genus Amphistegina emerged in the Eocene under higher atmospheric CO2 concentrations than present and experimental studies have shown that these foraminifers can sustain shell-growth rates under elevated pCO2. Warming temperatures also increase metabolic rates, increasing the energetic advantages of algal symbiosis. As surface waters continue to warm, the already elevated salinity and alkalinity in the eastern and central Mediterranean should further enhance carbonate production by A. lobifera and possibly by other benthic foraminifers that host algal symbionts. Observed rates of accumulation by hydrodynamic concentration of dead shells by nearshore wave action are comparable to rates of ongoing sea-level rise. Might this return of prolific shallow-water carbonate production ultimately prove at least locally beneficial as climate change progresses?
Continue reading ‘Why Amphistegina lobifera, a tropical benthic foraminiferal species, is thriving at temperate latitudes in the Mediterranean Sea’Lipid droplets in endosymbiotic Symbiodiniaceae spp. associated with corals
Published 20 August 2024 Science ClosedTags: biological response, BRcommunity, chemistry, corals, protists
Symbiodiniaceae species is a dinoflagellate that plays a crucial role in maintaining the symbiotic mutualism of reef-building corals in the ocean. Reef-building corals, as hosts, provide the nutrition and habitat to endosymbiotic Symbiodiniaceae species and Symbiodiniaceae species transfer the fixed carbon to the corals for growth. Environmental stress is one of the factors impacting the physiology and metabolism of the corals-dinoflagellate association. The environmental stress triggers the metabolic changes in Symbiodiniaceae species resulting in an increase in the production of survival organelles related to storage components such as lipid droplets (LD). LDs are found as unique organelles, mainly composed of triacylglycerols surrounded by phospholipids embedded with some proteins. To date, it has been reported that investigation of lipid droplets significantly present in animals and plants led to the understanding that lipid droplets play a key role in lipid storage and transport. The major challenge of investigating endosymbiotic Symbiodiniaceae species lies in overcoming the strategies in isolating lesser lipid droplets present in its intercellular cells. Here, we review the most recent highlights of LD research in endosymbiotic Symbiodiniaceae species particularly focusing on LD biogenesis, mechanism, and major lipid droplet proteins. Moreover, to comprehend potential novel ways of energy storage in the symbiotic interaction between endosymbiotic Symbiodiniaceae species and its host, we also emphasize recent emerging environmental factors such as temperature, ocean acidification, and nutrient impacting the accumulation of lipid droplets in endosymbiotic Symbiodiniaceae species.
Continue reading ‘Lipid droplets in endosymbiotic Symbiodiniaceae spp. associated with corals’Review of the protist Labyrinhula spp. and its relationship to seagrass disease under the influence of anthropogenic activities
Published 5 August 2024 Science ClosedTags: biological response, BRcommunity, chemistry, phanerogams, physiology, protists, review
Anthropogenic activities are driving significant changes in coastal ecological environments, increasingly spotlighting microorganisms associated with seagrass bed ecosystems. Labyrinthula is primarily recognized as a saprophytic protist associated with marine detritus, and it also acts as an opportunistic pathogen affecting marine algae, terrestrial plants and mollusks, especially in coastal environments. The genus plays a key role in the decomposition of marine detritus, facilitated by its interactions with diatoms and through the utilization of a diverse array of carbohydrate-active enzymes to decompose seagrass cell walls. However, human activities have significantly influenced the prevalence and severity of seagrass wasting disease (SWD) through factors such as climate warming, increased salinity and ocean acidification. The rise in temperature and salinity, exacerbated by human-induced climate change, has been shown to increase the susceptibility of seagrass to Labyrinthula, highlighting the adaptability of pathogen to environmental stressors. Moreover, the role of seagrass in regulating pathogen load and their immune response to Labyrinthula underscore the complex dynamics within these marine ecosystems. Importantly, the genotype diversity of seagrass hosts, environmental stress factors and the presence of marine organisms such as oysters, can influence the interaction mechanisms between seagrass and Labyrinthula. Besides, these organisms have the potential to both mitigate and facilitate pathogen transmission. The complexity of these interactions and their impacts driven by human activities calls for the development of comprehensive multi-factor models to better understand and manage the conservation and restoration of seagrass beds.
Continue reading ‘Review of the protist Labyrinhula spp. and its relationship to seagrass disease under the influence of anthropogenic activities’Symbiosis under stress: unraveling the interplay of ocean acidification and rising temperatures on Acropora Samoensis (staghorn coral)
Published 18 July 2024 Science ClosedTags: biological response, BRcommunity, chemistry, corals, laboratory, morphology, multiple factors, physiology, protists, temperature
This experiment explores the response of marine organisms to the combined effects of ocean acidification and rising temperatures, with a focus on coral reef ecosystems. As global climate change threatens profound declines in coral reefs, understanding the multifaceted impacts of these stressors becomes crucial. The study observes cellular changes in A. samoensis tissues in four different groups, including control, Temp, pH, and Temp and pH. Results indicate significant breakdown of membrane compartmentalization and cell junctions, with notable degradation and calcium carbonate crystallization in pH-stressed samples. Additionally, chlorophyll extraction data support coral bleaching due to the expulsion of zooxanthellae. These findings underscore the severe impact of pH and temperature variations on coral health, with pH conditions exhibiting a stronger effect. The study concludes by proposing a follow-up experiment involving the addition of carbon-fixing plants to mitigate environmental stressors and enhance coral resilience, aiming to contribute to the conservation of coral reef ecosystems in the face of climate change challenges.
Continue reading ‘Symbiosis under stress: unraveling the interplay of ocean acidification and rising temperatures on Acropora Samoensis (staghorn coral)’Revisiting 20 years of coral–algal interactions: global patterns and knowledge gaps
Published 1 July 2024 Science ClosedTags: algae, biological response, BRcommunity, corals, crustaceans, echinoderms, protists, review
Coral–algal interactions are pivotal in reef ecosystems globally as they can scale up ecosystem levels and lead to dominance shifts. In this study, we conducted a systematic review of global coral–algal interactions, identifying the most studied locations, species, and types of interactions. We then assessed how these interactions may be impacted by consumers and climate change. Over the past 20 years (2001–2020), coral and algae interactions were mostly explored in the Pacific, and the Caribbean and US East Coast, where branching and massive corals were the focus, while other coral growth forms received less attention, and effects on algae were often overlooked. Adult corals were generally reported to be damaged when directly interacting with algae through physical abrasion or allelopathy. Conversely, algae interactions were found to have a positive impact on juvenile corals by facilitating larval recruitment and settlement. As expected, coral–algal interactions and the type of coral–algal relationships vary globally, most likely due to differences in abiotic conditions, community composition and the number of studies performed in a region. Despite the large emphasis on the role of consumers in controlling coral–algal interactions, few studies directly explored the effects of herbivory on coral–algal interactions. Given the growing evidence that ocean warming and acidification can reduce the competitive ability of corals, understanding the dynamic relationships between coral, algae, and consumers under future climate change conditions is crucial in predicting future coral recruitment potential and reef composition patterns. Here, we highlight the main findings from coral–algal interaction studies performed in the last 20 year and point to future directions, such as: 1) diversifying location, coral species, growth forms and life phases; 2) considering effects on both sides of interaction, not neglecting effects on algae; and 3) taking a closer look into the role of consumers and microbiomes. Advancing our understanding of coral–algal interactions, as well as how these interactions shift under changing conditions, is critical in predicting how coral reef ecosystems may operate in the future.
Continue reading ‘Revisiting 20 years of coral–algal interactions: global patterns and knowledge gaps’Intraspecific variation in response to elevated pCO2 and temperature in the branching reef coral Acropora digitifera from different habitats
Published 27 June 2024 Science ClosedTags: biological response, BRcommunity, calcification, chemistry, corals, laboratory, morphology, mortality, multiple factors, North Pacific, photosynthesis, protists, temperature
Ocean acidification (OA) and ocean warming (OW) affect the calcification of corals, and intraspecific variations in response to these stressors in the population level need to be clarified for better future predictions. Using Acropora digitifera as our subject, we examined the intraspecific variability in calcification and maximum quantum yield (Fv/Fm) of photosystem II of symbiotic zooxanthella in responses to OA, OW, and OA + OW. Samples were taken from two different sites: Sesoko Station (warmer) and Sesoko South (cooler) in Okinawa, Japan. Calcification rates varied between the two sites, and noticeable differences were observed only among coral colonies from the Sesoko South site, specifically under control and OA treatments. Furthermore, Fv/Fm showed no variation between the sites due to those stresses. Hence, the calcification rates among A. digitifera colonies varied by habitat, and we found within-site variation only in the lower temperature location, Sesoko South. We observed diminished variation in response among colonies in the warmer site. The adapting to diverse environmental conditions and responding to changes such as seawater pCO2 and temperature, may lead to differences in sensitivity between the two populations to OA, OW, and OA + OW. These intraspecific variation could arise from factors like acclimatizations, the influence of specific genotypes, or phenotypic plasticity of the colonies.
Continue reading ‘Intraspecific variation in response to elevated pCO2 and temperature in the branching reef coral Acropora digitifera from different habitats’Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons
Published 20 June 2024 Science ClosedTags: abundance, biological response, BRcommunity, calcification, chemistry, community composition, corals, dissolution, laboratory, morphology, North Atlantic, otherprocess, primary production, protists, respiration
As the balance between erosional and constructive processes on coral reefs tilts in favor of framework loss under human-induced local and global change, many reef habitats worldwide degrade and flatten. The resultant generation of coral rubble and the beds they form can have lasting effects on reef communities and structural complexity, threatening the continuity of reef ecological functions and the services they provide. To comprehensively capture changing framework processes and predict their evolution in the context of climate change, heavily colonized rubble fragments were exposed to ocean acidification (OA) conditions for 55 days. Controlled diurnal pH oscillations were incorporated in the treatments to account for the known impact of diel carbonate chemistry fluctuations on calcification and dissolution response to OA. Scenarios included contemporary pH (8.05 ± 0.025 diel fluctuation), elevated OA (7.90 ± 0.025), and high OA (7.70 ± 0.025). We used a multifaceted approach, combining chemical flux analyses, mass alteration measurements, and computed tomography scanning images to measure total and chemical bioerosion, as well as chemically driven secondary calcification. Rates of net carbonate loss measured in the contemporary conditions (1.36 kg m−2 year−1) were high compared to literature and increased in OA scenarios (elevated: 1.84 kg m−2 year−1 and high: 1.59 kg m−2 year−1). The acceleration of these rates was driven by enhanced chemical dissolution and reduced secondary calcification. Further analysis revealed that the extent of these changes was contingent on the density of the coral skeleton, in which the micro- and macroborer communities reside. Findings indicated that increased mechanical bioerosion rates occurred in rubble with lower skeletal density, which is of note considering that corals form lower-density skeletons under OA. These direct and indirect effects of OA on chemical and mechanical framework-altering processes will influence the permanence of this crucial habitat, carrying implications for biodiversity and reef ecosystem function.
Continue reading ‘Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons’Respiratory protein-driven selectivity during the Permian–Triassic mass extinction
Published 8 April 2024 Science ClosedTags: brachiopods, mortality, paleo, physiology, protists
Extinction selectivity determines the direction of macroevolution, especially during mass extinction; however, its driving mechanisms remain poorly understood. By investigating the physiological selectivity of marine animals during the Permian–Triassic mass extinction, we found that marine clades with lower O2-carrying capacity hemerythrin proteins and those relying on O2 diffusion experienced significantly greater extinction intensity and body-size reduction than those with higher O2-carrying capacity hemoglobin or hemocyanin proteins. Our findings suggest that animals with high O2-carrying capacity obtained the necessary O2 even under hypoxia and compensated for the increased energy requirements caused by ocean acidification, which enabled their survival during the Permian–Triassic mass extinction. Thus, high O2-carrying capacity may have been crucial for the transition from the Paleozoic to the Modern Evolutionary Fauna.
Continue reading ‘Respiratory protein-driven selectivity during the Permian–Triassic mass extinction’Gene expression of pocillopora damicornis coral larvae in response to acidification and ocean warming
Published 27 March 2024 Science ClosedTags: biological response, BRcommunity, corals, laboratory, molecular biology, multiple factors, North Pacific, physiology, protists, temperature
Objectives
The endosymbiosis with Symbiodiniaceae is key to the ecological success of reef-building corals. However, climate change is threatening to destabilize this symbiosis on a global scale. Most studies looking into the response of corals to heat stress and ocean acidification focus on coral colonies. As such, our knowledge of symbiotic interactions and stress response in other stages of the coral lifecycle remains limited. Establishing transcriptomic resources for coral larvae under stress can thus provide a foundation for understanding the genomic basis of symbiosis, and its susceptibility to climate change. Here, we present a gene expression dataset generated from larvae of the coral Pocillopora damicornis in response to exposure to acidification and elevated temperature conditions below the bleaching threshold of the symbiosis.
Data description
This dataset is comprised of 16 samples (30 larvae per sample) collected from four treatments (Control, High pCO2, High Temperature, and Combined pCO2 and Temperature treatments). Freshly collected larvae were exposed to treatment conditions for five days, providing valuable insights into gene expression in this vulnerable stage of the lifecycle. In combination with previously published datasets, this transcriptomic resource will facilitate the in-depth investigation of the effects of ocean acidification and elevated temperature on coral larvae and its implication for symbiosis.
Continue reading ‘Gene expression of pocillopora damicornis coral larvae in response to acidification and ocean warming’Adverse environmental perturbations may threaten kelp farming sustainability by exacerbating enterobacterales diseases
Published 25 March 2024 Science ClosedTags: algae, biological response, community composition, field, laboratory, light, molecular biology, morphology, mortality, multiple factors, North Pacific, otherprocess, physiology, prokaryotes, protists, reproduction
Globally kelp farming is gaining attention to mitigate land-use pressures and achieve carbon neutrality. However, the influence of environmental perturbations on kelp farming remains largely unknown. Recently, a severe disease outbreak caused extensive kelp mortality in Sanggou Bay, China, one of the world’s largest high-density kelp farming areas. Here, through in situ investigations and simulation experiments, we find indications that an anomalously dramatic increase in elevated coastal seawater light penetration may have contributed to dysbiosis in the kelp Saccharina japonica’s microbiome. This dysbiosis promoted the proliferation of opportunistic pathogenic Enterobacterales, mainly including the genera Colwellia and Pseudoalteromonas. Using transcriptomic analyses, we revealed that high-light conditions likely induced oxidative stress in kelp, potentially facilitating opportunistic bacterial Enterobacterales attack that activates a terrestrial plant-like pattern recognition receptor system in kelp. Furthermore, we uncover crucial genotypic determinants of Enterobacterales dominance and pathogenicity within kelp tissue, including pathogen-associated molecular patterns, potential membrane-damaging toxins, and alginate and mannitol lysis capability. Finally, through analysis of kelp-associated microbiome data sets under the influence of ocean warming and acidification, we conclude that such Enterobacterales favoring microbiome shifts are likely to become more prevalent in future environmental conditions. Our study highlights the need for understanding complex environmental influences on kelp health and associated microbiomes for the sustainable development of seaweed farming.
Continue reading ‘Adverse environmental perturbations may threaten kelp farming sustainability by exacerbating enterobacterales diseases’Accelerated nitrogen cycling on Mediterranean seagrass leaves at volcanic CO2 vents
Published 22 March 2024 Science ClosedTags: adaptation, biogeochemistry, biological response, laboratory, Mediterranean, molecular biology, nitrogen fixation, otherprocess, phanerogams, physiology, prokaryotes, protists, vents
Seagrass meadows form highly productive and diverse ecosystems in coastal areas worldwide, where they are increasingly exposed to ocean acidification (OA). Efficient nitrogen (N) cycling and uptake are essential to maintain plant productivity, but the effects of OA on N transformations in these systems are poorly understood. Here we show that complete N cycling occurs on leaves of the Mediterranean seagrass Posidonia oceanica at a volcanic CO2 vent near Ischia Island (Italy), with OA affecting both N gain and loss while the epiphytic microbial community structure remains largely unaffected. Daily leaf-associated N2 fixation contributes to 35% of the plant’s N demand under ambient pH, while it contributes to 45% under OA. Nitrification potential is only detected under OA, and N-loss via N2 production increases, although the balance remains decisively in favor of enhanced N gain. Our work highlights the role of the N-cycling microbiome in seagrass adaptation to OA, with key N transformations accelerating towards increased N gain.
Continue reading ‘Accelerated nitrogen cycling on Mediterranean seagrass leaves at volcanic CO2 vents’Ocean acidification and food availability impacts on the metabolism and grazing in a cosmopolitan herbivorous protist Oxyrrhis marina
Published 8 March 2024 Science ClosedTags: abundance, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, otherprocess, performance, physiology, primary production, protists, respiration, zooplankton
The heterotrophic dinoflagellate Oxyrrhis marina is an essential microzooplankton in coastal waters, linking the energy transfer from phytoplankton to higher trophic levels. It is of general significance to investigate how it responds and acclimates to ocean acidification (OA), especially under varied availabilities of food. Here, O. marina was exposed and acclimated to three pCO2 levels (LC: 415, MC:1000, HC:1500 μatm) for 60 days, and then was further grown under the CO2 levels with different levels of food (the microalgae Dunaliella salina) availability for about 8 generations. The OA treatments did not significantly hamper its growth and ingestion rates even under the reduced food availability and starvation (deprived of the microalgae), which significantly reduced its growth rate. While the impacts of OA on the growth and ingestion rates of O. marina were insignificant, the OA treatments appeared to have resulted in a faster decline of the heterotrophic dinoflagellate cells during the starvation period. Nevertheless, the acidic stress under the elevated pCO2 of 1000 or 1500 μatm decreased its respiration by about 53% or 59% with the high and by about 26% or 23% with the low food availability, respectively. Such OA-repressed respiration was also significant during the starvation period. On the other hand, the OA treatments and deprivation of the microalgae synergistically reduced the cellular quota of particulate organic C, N and P, resulting in a reduction of food value of the heterotrophic dinoflagellate as prey. In conclusion, our results show that O. marina is highly resilient to future ocean acidification by reducing its respiration and sustaining its ingestion of microalgae.
Continue reading ‘Ocean acidification and food availability impacts on the metabolism and grazing in a cosmopolitan herbivorous protist Oxyrrhis marina’Nannofossil imprints across the Paleocene-Eocene thermal maximum
Published 29 February 2024 Science ClosedTags: BRcommunity, chemistry, field, morphology, North Atlantic, paleo, phytoplankton, protists, sediment
The Paleocene–Eocene thermal maximum (PETM; ca. 56 Ma) geological interval records a marked decline in calcium carbonate (CaCO3) in seafloor sediments, potentially reflecting an episode of deep- and possibly shallow-water ocean acidification. However, because CaCO3 is susceptible to postburial dissolution, the extent to which this process has influenced the PETM geological record remains uncertain. Here, we tested for evidence of postburial dissolution by searching for imprint fossils of nannoplankton preserved on organic matter. We studied a PETM succession from the South Dover Bridge (SDB) core, Maryland, eastern United States, and compared our imprint record with previously published data from traditionally sampled CaCO3-preserved nannoplankton body fossils. Abundant imprints through intervals devoid of CaCO3 would signify that postburial dissolution removed much of the CaCO3 from the rock record. Imprints were recorded from most samples but were rare and of low diversity. Body fossils were substantially more numerous and diverse, capturing a more complete record of the living nannoplankton communities through the PETM. The SDB succession records a dissolution zone/low-carbonate interval at the onset of the PETM, through which nannoplankton body fossils are rare. No nannoplankton imprints were found from this interval, suggesting that the rarity of body fossils is unlikely to have been the result of postburial dissolution. Instead, our findings suggest that declines in CaCO3 through the PETM at the SDB location were the result of: (1) biotic responses to changes that were happening during this event, and/or (2) CaCO3 dissolution that occurred before lithification (i.e., in the water column or at the seafloor).
Continue reading ‘Nannofossil imprints across the Paleocene-Eocene thermal maximum’Modeled foraminiferal calcification and strontium partitioning in benthic foraminifera helps reconstruct calcifying fluid composition
Published 5 February 2024 Science ClosedTags: biological response, calcification, individualmodeling, modeling, physiology, protists
Foraminifera are unicellular organisms that inhabit the oceans. They play an important role in the global carbon cycle and record valuable paleoclimate information through the uptake of trace elements such as strontium into their calcitic shells. Understanding how foraminifera control their internal fluid composition to make calcite is important for predicting their response to ocean acidification and for reliably interpreting the chemical and isotopic compositions of their shells. Here, we model foraminiferal calcification and strontium partitioning in the benthic foraminifera Cibicides wuellerstorfi and Cibicidoides mundulus based on insights from inorganic calcite experiments. The numerical model reconciles inter-ocean and taxonomic differences in benthic foraminifer strontium partitioning relationships and enables us to reconstruct the composition of the calcifying fluid. We find that strontium partitioning and mineral growth rates of foraminiferal calcite are not strongly affected by changes in external seawater pH (within 7.8–8.1) and dissolved inorganic carbon (DIC, within 2100–2300 μmol/kg) due to a regulated calcite saturation state at the site of shell formation.
Continue reading ‘Modeled foraminiferal calcification and strontium partitioning in benthic foraminifera helps reconstruct calcifying fluid composition’Atmospheric CO2 estimates for the Late Oligocene and Early Miocene using multi-species cross-calibrations of boron isotopes
Published 31 January 2024 Science ClosedTags: biological response, BRcommunity, chemistry, methods, paleo, protists, sediment
Abstract
The boron isotope (δ11B) proxy for seawater pH is a tried and tested means to reconstruct atmospheric CO2 in the geologic past, but uncertainty remains over how to treat species-specific calibrations that link foraminiferal δ11B to pH estimates prior to 22 My. In addition, no δ11B-based reconstructions of atmospheric CO2 exist for wide swaths of the Oligocene (33–23 Ma), and large variability in CO2 reconstructions during this epoch based on other proxy evidence leaves climate evolution during this period relatively unconstrained. To add to our understanding of Oligocene and early Miocene climate, we generated new atmospheric CO2 estimates from new δ11B data from fossil shells of surface-dwelling planktic foraminifera from the mid-Oligocene to early Miocene (∼28–18 Ma). We estimate atmospheric CO2 of ∼680 ppm for the mid-Oligocene, which then evolves to fluctuate between ∼500–570 ppm during the late Oligocene and between ∼420–700 ppm in the early Miocene. These estimates tend to trend higher than Oligo-Miocene CO2 estimates from other proxies, although we observe good proxy agreement in the late Oligocene. Reconstructions of CO2 fall lower than estimates from paleoclimate model simulations in the early Miocene and mid Oligocene, which indicates that more proxy and/or model refinement is needed for these periods. Our species cross-calibrations, assessing δ11B, Mg/Ca, δ18O, and δ13C, are able to pinpoint and evaluate small differences in the geochemistry of surface-dwelling planktic foraminifera, lending confidence to paleoceanographers applying this approach even further back in time.
Key points:
- We measure δ11B on multiple species of planktic foraminifera to generate new CO2 reconstructions for the late Oligocene and early Miocene
- Using a novel cross-calibration approach, we reconstruct CO2 of 500–680 ppm for the mid-late Oligocene and 420–700 ppm for the early Miocene
- Mean CO2 values tend to trend higher than other proxy estimates, but generally lower than paleoclimate model simulations
Early stage ecological communities on artificial algae showed no difference in diversity and abundance under ocean acidification
Published 24 January 2024 Science ClosedTags: abundance, algae, annelids, biological response, BRcommunity, calcification, chemistry, community composition, crustaceans, echinoderms, field, Mediterranean, mesocosms, mitigation, mollusks, otherprocess, photosynthesis, protists, respiration
Marine habitat-forming species create structurally complex habitats that host macroinvertebrate communities characterized by remarkable abundance and species richness. These habitat-forming species also play a fundamental role in creating favourable environmental conditions that promote biodiversity. The deployment of artificial structures is becoming a common practice to help offset habitat loss although with mixed results. This study investigated the suitability of artificial flexible turfs mimicking the articulated coralline algae (mimics) as habitat providers and the effect of ocean acidification (OA) on early stage ecological communities associated to flexible mimics and with the mature community associated to Ellisolandia elongata natural turfs. The mimics proved to be a suitable habitat for early stage communities. During the OA mesocosms experiment, the two substrates have been treated and analysed separately due to the difference between the two communities. For early stage ecological communities associated with the mimics, the lack of a biologically active substrate does not exacerbate the effect of OA. In fact, no significant differences were found between treatments in crustaceans, molluscs and polychaetes diversity and abundance associated with the mimics. In mature communities associated with natural turfs, buffering capability of E. elongata is supporting different taxonomic groups, except for molluscs, greatly susceptible to OA.
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