Ocean acidification (OA) and associated shifts in carbonate chemistry represent major threats to marine organisms, particularly calcifiers. OA effects can be influenced by other environmental variables, including the biotic environment. This study investigated the individual and interactive effects of OA and algal density, acting through biofilm composition, on post-larval and juvenile abalone (Haliotis tuberculata). In a three-month factorial experiment, abalone were exposed from metamorphosis onward to two pH conditions (ambient 8.0 and reduced 7.7) and two initial densities of the green alga Ulvella lens on settlement plates. Biofilm biomass and composition were characterised using spectral reflectance and HPLC pigment analysis. Biological (density, length), physiological (respiration rate), behavioural (hiding response) and shell parameters (colour, surface corrosion, strength) of abalone were measured throughout the experiment. Biofilm biomass and composition remained relatively stable under both pH conditions, though greater variability in algal biomass occurred at low initial Ulvella density. Post-larval density and total length decreased significantly under low pH, while high Ulvella density reduced juvenile length at 80 days, likely due to competition between algal groups. A pH × Ulvella interaction affected shell fracture resistance and colouration, but not metabolism or behaviour, indicating that juvenile abalone maintained vital functions. Overall, the results confirm the sensitivity of early H. tuberculata stages to moderate OA (−0.3 pH units) and highlight indirect macroalgal effects through changes in diatom communities. In natural environments, the capacity of abalone to cope with future OA will depend on complex trade-offs between direct acidification effects and food-related biotic interactions.
Continue reading ‘Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata’Posts Tagged 'phytoplankton'
Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata
Published 23 December 2025 Science ClosedTags: biological response, communityMF, laboratory, mollusks, morphology, multiple factors, North Atlantic, performance, phytoplankton, reproduction, respiration
Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock
Published 19 December 2025 Science ClosedTags: biological response, BRcommunity, corals, multiple factors, North Atlantic, performance, phytoplankton, temperature
Over the last several decades, Florida’s Coral Reef has been impacted by global and local stressors causing significant declines in living coral with no signs of natural recovery. Ocean warming, ocean acidification, and infectious diseases are major contributors to the precipitous loss of corals within this region. Since 2014, the stony coral tissue loss disease (SCTLD) outbreak has been particularly devastating, causing unprecedented mortality in over 20 massive coral species. As SCTLD is now endemic in the region, and threats from climate change are likely to persist, studying the disease susceptibility of different coral genotypes under future environmental scenarios is vital for effective restoration. Here, we exposed Orbicella faveolata and Pseudodiploria clivosa genotypes to wild colonies showing signs consistent with SCTLD immediately following a 2-month long exposure to ocean warming (OW) and ocean acidification (OA) scenarios. Corals were exposed to SCTLD for 3 weeks while maintaining the environmental treatments. For both species, pre-exposure to OW and OA scenarios did not make corals more susceptible to SCTLD. However, three genotypes hosting higher levels of Breviolum were at increased risk for showing SCTLD signs under these conditions. One O. faveolata genotype was consistently resistant to SCTLD under the different scenarios, suggesting that natural levels of resistance exist in coral restoration broodstock. Understanding why this genotype could withstand exposure to these stressors may be critical for ensuring survival of restored populations into the future.
Continue reading ‘Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock’Seasonal variations of physico-chemical variables interaction and their influence on phytoplankton and pCO2 dynamics in the Southwest Bay of Bengal
Published 12 December 2025 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, community composition, field, Indian, otherprocess, phytoplankton
The carbonate system and nutrient dynamics play a crucial role in regulating phytoplankton productivity and carbon cycling in tropical coastal ecosystems, which are highly sensitive to climate change and anthropogenic activities. The present study investigates the spatio-temporal variability of physico-chemical parameters, nutrient dynamics and their influence on phytoplankton community structure along the southwest coast of Bay of Bengal (SWBoB), with particular focus on their relationship with partial pressure of carbon di-oxide (pCO₂). Seasonal sampling was carried out entirely with onboard cruise programs, with each cruise representing different season such as pre-monsoon, monsoon, post-monsoon and summer. The study covered SWBoB among six stations namely Tuticorin, Nagapattinam, Poombuhar, Pondicherry, Mahabalipuram and Chennai during 2022–2023. A total of 77 phytoplankton species representing five taxonomic classes were identified and quantified, where minimum and maximum phytoplankton density were observed during summer (7.498 × 103 cells. L-1) and pre-monsoon (7.0014 × 104 cells. L-1) respectively. A pronounced spatio-temporal variations were observed in physico-chemical parameters and nutrients with peak phytoplankton density and pCO₂ value (487.47 µatm) during pre-monsoon period were attributed to enhanced microbial respiration, riverine input and upwelling of CO₂-rich subsurface waters. In contrast, reduced pCO₂ level (274.27 µatm) observed during summer coincided with water column stratification, nutrient limitation and elevated photosynthetic uptake by phytoplankton. Canonical Correspondence Analysis (CCA) indicated a strong association were attributed nutrient availability and phytoplankton assemblages, with diatoms prevailing under nutrient-rich and moderate pCO₂ conditions, simultaneously dinoflagellate dominated at high pCO₂ conditions. A significant positive relationship between pCO₂ and phytoplankton species with canonical score (0.91) of Noctiluca scintillans highlights the sensitivity of SwBoB productivity to carbon system variability. During pre-monsoon, high pCO₂ (487.47 µatm), chlorophyll-a (3.10 µg L-1) and phytoplankton density (7.0014 × 104 cells. L-1) at station T2, co-dominated by both diatom (46 %) and dinoflagellates (40 %), specifically Noctiluca scintillans (6.32 %). This indicated that nutrient enrichment and CO₂-rich upwelling enhanced phytoplankton productivity and carbon dynamics. These findings imply that pCO₂ variations, determined by temperature, salinity and nutrient inputs which influence the phytoplankton structure and productivity, impacts carbon cycling and ecosystem dynamics in the SWBoB region. This study provides valuable insights into carbon cycling and ecosystem functioning, crucial for sustaining regional fisheries and anticipating monsoon-driven changes in coastal productivity.
Continue reading ‘Seasonal variations of physico-chemical variables interaction and their influence on phytoplankton and pCO2 dynamics in the Southwest Bay of Bengal’Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea
Published 5 December 2025 Science ClosedTags: biogeochemistry, biological response, community composition, laboratory, mesocosms, North Pacific, otherprocess, phytoplankton, primary production, respiration
Anthropogenic CO2 emissions and their continuous dissolution into seawater lead to seawater pCO2 rise and ocean acidification (OA). Phytoplankton groups are known to be differentially affected by carbonate chemistry changes associated with OA in different regions of contrasting physical and chemical features. To explore responses of phytoplankton to OA in the Chinese coastal waters, we conducted a mesocosm experiment in a eutrophic bay of the southern East China Sea under ambient (410 μatm, AC) and elevated (1000 μatm, HC) pCO2 levels. The HC stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness were reduced during this stage due to the rapid nutrient consumption and diatom blooms, and the subsequent shift from diatoms to hetero-dinoflagellates led to a decline in primary production during the mid and later phases under nutrient depletion. Such suppression of diatom-to-dinoflagellate succession occurred with enhanced remineralization of organic matter under the HC conditions, with smaller phytoplankton becoming dominant for the sustained primary production. Our findings indicate that, the impacts of OA on phytoplankton diversity in the coastal water of the southern East China Sea depend on availability of nutrients, with primary productivity and biodiversity of phytoplankton reduced in the eutrophicated coastal water.
Continue reading ‘Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea’Experimental evidence of climate change effects on plankton community respiration in European coastal waters: current insights and knowledge gaps in tested disturbances and studied areas
Published 2 December 2025 Science ClosedTags: biological response, physiology, phytoplankton, respiration, review
Plankton community respiration (PCR) plays a central role in aquatic ecosystems, driving the breakdown of organic matter and influencing global carbon cycling through its contribution to the production and consumption of carbon and oxygen. Coastal areas, which serve as critical interfaces between terrestrial and marine ecosystems, are regarded as metabolic hotspots in the oceans, due to their intense biological and biogeochemical activities. Additionally, they are particularly sensitive to the impacts of global climate change. In this regard, this review synthesizes experimental evidence to explore how environmental constraints and climate drivers affect PCR in European coastal waters. In total, 46 studies were found in which PCR was measured during experiments testing the effects of one or multiple global climate change drivers in European coastal waters. Among them, the majority of experiments focused on changes in temperature, nutrient concentrations and stoichiometry, and/or pH, while other stressors were less studied. Many experiments confirmed theoretical predictions, notably regarding the predicted positive effects of increased temperature and nutrient concentrations on metabolism, but more complex responses, often linked to trophic cascade mechanisms and thresholds between positive and negative feedbacks were also often reported. Overall, this review, the first comprehensive synthesis of experimental evidence on PCR in European coastal waters, highlights critical knowledge gaps, notably regarding non- and understudied areas and understudied interactions between stressors that occurs jointly in natural ecosystems. Future research should aim to integrate controlled experiments, long-term monitoring, and modeling approaches to deepen our understanding of PCR dynamics under changing environmental conditions and to predict potential feedbacks to global climate processes.
Continue reading ‘Experimental evidence of climate change effects on plankton community respiration in European coastal waters: current insights and knowledge gaps in tested disturbances and studied areas’The larva-Symbiodiniaceae association at risk: putative impacts of climate change on reproduction, dispersal, and recruitment in coral reefs
Published 24 November 2025 Science ClosedTags: biological response, BRcommunity, cnidaria, corals, mollusks, physiology, phytoplankton, porifera, reproduction, review
The relationship between invertebrates and Symbiodiniaceae dinoflagellates is the ecological foundation of diverse and productive coral reef ecosystems. Climate change-induced breakdown of this partnership, i.e., bleaching, is repeatedly driving widespread reef degradation. Thus, the future trajectory of this ecosystem depends on the reproduction and dispersal capacity of invertebrate-Symbiodiniaceae symbiosis. This review examines how climate change affects the biology of larvae from three invertebrate phyla—Porifera, Cnidaria, and Mollusca—that host Symbiodiniaceae, focusing on differences in symbiont transmission mode, symbiont location, and the larvae´s reliance on these associations. Due to limited research on Porifera and Mollusca hosts, most knowledge of larvae-Symbiodiniaceae associations stems from coral larvae patterns. The myriads of combinations of genetic and ecophysiologically distinct hosts and symbionts result in highly context-dependent responses to warming, but symbiotic larvae tend to be more susceptible to oxidative stress and show higher mortality than aposymbiotic larvae. While ocean acidification has little direct effect on the algal symbionts, it impacts larvae variably, especially calcifying larvae (e.g., mollusks), which suffer from impaired calcification and higher mortality. Climate change also impairs the reproductive processes of Symbiodiniaceae-bearing invertebrates, reducing gamete output, causing asynchronous spawning, and lowering larval survival. These effects will result in a persistent decline in recruitment with increased larval retention, consequently reducing reef connectivity and genetic diversity, thus weakening ecosystem resilience. This underscores the urgent need to hasten knowledge on larval ecology under climate change and the functional role of symbionts to better inform marine conservation planning and to incorporate larval ecology in the future predictions.
Continue reading ‘The larva-Symbiodiniaceae association at risk: putative impacts of climate change on reproduction, dispersal, and recruitment in coral reefs’Calcifying plankton: from biomineralization to global change
Published 28 October 2025 Science ClosedTags: biological response, mollusks, physiology, phytoplankton, protists, review, zooplankton
BACKGROUND
The production and dissolution of calcium carbonate (CaCO3) is a key component of the ocean carbon cycle. In the open ocean, nearly all CaCO3 is produced by three groups of calcifying plankton: coccolithophores, foraminifers, and pteropods. These taxonomically and functionally diverse organisms play a major role in ocean biogeochemistry by modulating air-sea CO2 exchange, and facilitating the export of carbon and alkalinity to depth.
Despite their biogeochemical importance, these groups are typically considered separately, precluding an integrated understanding. Yet the pathways by which CaCO3 is produced and cycled through the ocean have important consequences for the carbon cycle and ecosystem functioning. Notably, none of the Earth system models included in the current Coupled Model Intercomparison Project (CMIP6) explicitly represents these groups of organisms. Here, we review the distinct functional traits of coccolithophores, foraminifers, and pteropods to elucidate how these traits shape their global distributions, vulnerabilities to climate change and acidification, and their role in modulating ocean chemistry and the Earth system.
ADVANCES
Recent advances in data compilation at multiple levels offer a comprehensive but still incomplete view of the CaCO3 cycle, from biomineralization up to the global ocean, with different traits leading to differing vulnerabilities to environmental change. For example, coccolithophores, as primary producers, are relatively less affected by changes in oxygen concentration compared with heterotrophs, but are particularly sensitive to ocean acidification because of the proton load generated during intracellular calcification, which requires effective pH regulation and proton expulsion. Differing resource requirements contribute to the geographic distributions of each group, while traits such as body size and turnover rate are fundamentally linked to global production, export, dissolution, and burial. Compiling these data allows us to compare the markedly different fates of the CaCO3 produced by each group, from surface production through export to eventual sediment burial. A major imbalance exists in the global CaCO3 cycling related to each calcifying plankton group, with key uncertainties, especially in rates of group-specific production and shallow biologically mediated dissolution. Current best estimates indicate that a large fraction of coccolithophore-derived CaCO3—the dominant source of CaCO3 in the ocean—is dissolved and recycled in the upper ocean. This underscores the central role of ecological processes such as predation, particle aggregation, and microbial respiration in shaping ocean carbonate chemistry.
We suggest that the overlooked process of shallow dissolution, mainly of coccolithophores, is also likely at play within the geological record of this group.
OUTLOOK
The three major groups of calcifying plankton play essential but distinct roles within ocean ecosystems and the marine carbon cycle. Their diverse traits govern global distributions, production, export, and their differing response to environmental change. The magnitude of biologically mediated CaCO3 dissolution in the upper ocean remains broadly unrecognized, with implications for both the global alkalinity budget and interpretations of the fossil record. Sediment cores provide a fossil record going back 65 million years, revealing large variation in organism size and diversity likely linked to changes in seawater carbonate chemistry (acidification) and warming. The extent to which shallow, selective dissolution has biased this record remains an important unresolved question. Addressing discrepancies between CaCO3 production and export from the upper ocean will require renewed focus on both quantifying and understanding the individual and combined contribution of these groups, as well as the biological processes driving shallow dissolution. These efforts are also critical for incorporating a mechanistically resolved CaCO3 cycle into future climate models, thereby supporting a more integrated view of ocean biogeochemistry under climate change.
Continue reading ‘Calcifying plankton: from biomineralization to global change’Oxidative stress and histological alterations in coral Briareum violacea co-exposed to ocean acidification and microplastic stressors
Published 17 October 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, North Pacific, performance, physiology, phytoplankton, plastics
Ocean acidification and microplastic pollution are two major stressors threatening coral health, yet their combined impacts and underlying mechanisms remain poorly understood. This study investigated the combined effects of ocean acidification and microplastics exposure to coral health. Briareum violacea was exposed to pH at 7.7, 7.5, and 7.3 combined with polyethylene microplastic (PE-MP; 50 mg/L) for 21 days. Polyp length and behavioral adaptability were monitored daily, while coral was collected on days 14 and 21 to assess Symbiodiniaceae density, antioxidant enzyme activity, and histopathological alterations. Results showed that combined exposure to different pH (7.7, 7.5, and 7.3) and PE-MP significantly impaired coral condition, reduced polyp length and Symbiodiniaceae density, along with intensified oxidative stress and tissue damage compared to single stressors. These findings underscore coral vulnerability under combined stressors, emphasizing the necessity for future research to address long-term ecological consequences and resilience mechanisms in coral reef ecosystems.
Continue reading ‘Oxidative stress and histological alterations in coral Briareum violacea co-exposed to ocean acidification and microplastic stressors’Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)
Published 10 October 2025 Science ClosedTags: biogeochemistry, biological response, multiple factors, otherprocess, phytoplankton, prokaryotes, review, temperature
Nitrogen uptake by phytoplankton and nitrification mediated by nitrifying microorganisms in the upper ocean are key processes affecting marine productivity and carbon sequestration. How these two critical nitrogen cycle processes respond to the dual stressors of ocean acidification and warming represents a pressing research frontier in marine biogeochemical cycles and global change. Elucidating this issue will provide a theoretical foundation for accurately assessing future changes in ocean productivity and the efficiency of the biological pump. However, most existing studies rely on laboratory pure culture experiments, which may fail to adequately reflect the complex interactions between phytoplankton and nitrifying microorganisms in natural marine ecosystems and their responses to changes in environmental factors. The impacts and mechanisms of ocean acidification and warming on nitrogen uptake and nitrification are systematically summarized. In addition, more attention needs to be paid to other factors, such as strengthened ocean stratification and decreased dissolved oxygen contents, induced by ocean acidification and warming, which could indirectly affect nitrogen uptake and nitrification. Existing problems, such as insufficient in-situ monitoring of ecosystems, limited synergistic studies on multiple processes and stresses, and inadequate understanding of long-term adaptation processes, are highlighted. Finally, three key areas of research that need to be focused on in the future were prospected: ① to conduct the synchronous coupling analysis of nitrogen uptake and nitrification processes and clarify the interactive effects of acidification and warming, ② to explore the vertical differentiation response mechanisms of the above processes in the upper ocean, particularly in oligotrophic oceans, where critical knowledge gaps exist, and ③ to elucidate the long-term adaptation processes and nonlinear response laws of phytoplankton and nitrifying microorganisms. A three-in-one research framework is constructed in the spatial dimension, temporal scale and the experimental system to provide a scientific basis for evaluating the evolution of key nitrogen processes and marine productivity under global change.
Continue reading ‘Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)’Coral calcification resistance to acidification is physiologically linked with complex intracellular calcium ion dynamics between host and symbiont cells
Published 8 October 2025 Science ClosedTags: biological response, BRcommunity, calcification, corals, laboratory, molecular biology, North Pacific, phytoplankton
Coral calcification is a highly complex process with numerous caveats regarding the mechanisms that dictate productivity and function. Ion homeostasis, however, is the foremost physiological process unanimously shared among Scleractinia and essential for calcification. Consequently, changes to the seawater environment may elicit adverse effects on ion homeostasis. With increasing climate shifts, the physicochemical regime of our global ocean is changing rapidly. Responses of coral calcification to physicochemical change prevail in having little uniformity on an unambiguous mechanism of resistance. Therefore, this study chose a relatively tolerant Hawaiian coral, Montipora capitata to focus efforts on understanding ion homeostasis under chemical seawater manipulation designed to limit calcification. Results indicate a physiological hormesis (two-phase adaptive response) of overall coral host gene expression that was not shared with algal symbionts and decoupled from calcification rates. The sole ion homeostatic mechanism shown was calcium ion regulation by both the host and symbiont cells. Calcium ion homeostasis was also found to be mechanistically different between winter and summer seasons. Thus, potentially indicating complex interactions between host and symbiont cells, as well as the ability for M. capitata to promote calcification under stress. Putatively synthesized here are the physiological cascades and mechanisms of resistance to environmental triggers of acidosis and seasonal change. This work provides insight into linking calcium ion homeostasis with coral resistance and aims to suggest this mechanism as biomolecular indicator used in future assessments to compare tolerance.
Continue reading ‘Coral calcification resistance to acidification is physiologically linked with complex intracellular calcium ion dynamics between host and symbiont cells’Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario
Published 7 October 2025 Science ClosedTags: biogeochemistry, biological response, community composition, field, globalmodeling, modeling, otherprocess, phytoplankton
Ammonium (NH4+) is an important component of the ocean’s dissolved inorganic nitrogen (DIN) pool, especially in stratified marine environments where intense recycling of organic matter elevates its supply over other forms. Using a global-ocean biogeochemical model with good fidelity to the sparse NH4+ data that are available, we project increases in the NH4+: DIN ratio in over 98 % of the ocean by the end of the 21st century under a high-emission scenario. This relative enrichment of NH4+ is driven largely by circulation changes and secondarily by warming-induced increases in microbial metabolism, as well as reduced nitrification rates due to pH decreases. Supplementing our model projections with geochemical measurements and phytoplankton abundance data from Tara Oceans, we demonstrate that shifts in the form of DIN to NH4+ may impact phytoplankton communities by disadvantaging nitrate-dependent taxa like diatoms while promoting taxa better adapted to NH4+. This could have cascading effects on marine food webs, carbon cycling and fishery productivity. Overall, the form of bioavailable nitrogen emerges as a potentially underappreciated driver of ecosystem structure and function in the changing ocean.
Continue reading ‘Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario’Elevated pCO2 and temperature levels modulate the ratios of the photosynthetic methane production to CO2 fixation in the coccolithophorid Emiliania huxleyi
Published 6 October 2025 Science ClosedTags: biological response, laboratory, multiple factors, North Atlantic, photosynthesis, physiology, phytoplankton, temperature
Most phytoplankton species have been shown to release methane (CH4) during photosynthesis; however, little has been documented on how changed levels of CO2 at different temperatures affect their CH4 production along with photosynthetic C fixation. Here, we examined CH4 production and photosynthetic performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 μatm, HC) and ambient (415 μatm, LC) pCO2 levels at five temperatures (16, 20, 22, 24 and 27°C). The HC treatment slightly lowered the optimal temperature for growth and CH4 production, and temperature changes significantly affected both carbon fixation and CH4 production. Under suboptimal temperatures, increasing temperature from 16 to 20°C led to about 96% increase in CH4 production per POC and HC treatment further enhanced this increase by an additional 9%. In contrast, under super-optimal temperatures, a temperature rise by 4°C reduced the microalgal CH4 production per POC under HC treatment by about 24% compared to the control. The calculated CH4 production quotient (MPQ, CH4 released vs. CO2 fixed) ranged between 2 × 10−5−6 × 10−5, and showed a decreasing trend with increasing temperature under both pCO2 levels, implying that the CH4 production by this microalga is being affected by global ocean changes, and the CH4 produced by phytoplankton should be quantified and included in assessing the feedback of marine phytoplankton to climate change.
Continue reading ‘Elevated pCO2 and temperature levels modulate the ratios of the photosynthetic methane production to CO2 fixation in the coccolithophorid Emiliania huxleyi’Carbonate chemistry fitness landscapes inform diatom resilience to future perturbations
Published 22 September 2025 Science ClosedTags: biological response, growth, laboratory, physiology, phytoplankton, South Pacific
Marine diatoms are an abundant and ecologically important phytoplankton group susceptible to changing environmental conditions. Currently available data assessing diatom responses focus on empirical comparisons between present-day and future conditions, rather than exploring the mechanisms driving these responses. Here, we conducted high-resolution growth experiments to map the fitness of diatoms across broad carbonate chemistry landscapes. Our results reveal species-specific carbonate chemistry niches, which can be used to predict ecological shifts between species under changing conditions driven by ocean acidification or ocean alkalinity enhancement. The results demonstrate that changes in diatom fitness are almost exclusively driven by carbon dioxide and proton concentrations, with bicarbonate exerting no discernible effect. Thus, current assumptions regarding the role of bicarbonate as a primary carbon source supporting diatom growth may be overestimated. This study presents a methodological and conceptual framework as a foundation for future studies to collate data capable of predicting species-specific responses and shifts in ecological niches driven by changes in marine carbonate chemistry.
Continue reading ‘Carbonate chemistry fitness landscapes inform diatom resilience to future perturbations’Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis
Published 22 September 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, photosynthesis, physiology, phytoplankton, plastics, South Atlantic, temperature
Microplastic pollution is ubiquitous in the oceans. However, little is known about the physiological impact of microplastics on corals, particularly under predicted future ocean conditions. This study investigated the individual impacts of microplastic exposure (MP) and predicted future ocean conditions [ocean acidification and warming (OAW)] as well as the combination of these stressors (OAW+MP) on the growth and physiology of Acropora cervicornis, a threatened Caribbean coral and its associated symbiont, Symbiodiniaceae. After 22 days, the OAW+MP treatment resulted in more pronounced physiological changes than either stressor individually or the control. OAW conditions alone had minimal impacts, despite A. cervicornis generally being sensitive to thermal stress. The OAW+MP treatment and the MP treatment also disrupted the host-symbiont relationship evidenced by the higher symbiont densities relative to the control and the OAW treatments. Additionally, the OAW+MP treatment resulted in lower chlorophyll a per symbiont cell. Microplastic handling is energetically costly, possibly leading to changes in host-symbiont signaling. Photosynthetic efficiency was only marginally lower in the OAW+MP treatment, and values did not indicate photosystem damage. Negative host health impacts were found with the OAW+MP treatment exhibiting lower skeletal growth compared to the control and lower host protein concentrations compared to the OAW treatment. These results indicate that although short term microplastic exposure alone may not pose a significant threat to coral health, when adding additional stressors, it can further threaten the health and recovery of this already vulnerable species.
Continue reading ‘Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis’Particulate inorganic carbon pools by coccolithophores in low-oxygen–low-pH waters off the Southeast Pacific margin
Published 10 September 2025 Science ClosedTags: biogeochemistry, biological response, chemistry, field, phytoplankton, South Pacific
A predicted consequence of ocean acidification is the decrease in coccolithophore-produced particulate inorganic carbon (PIC) pools. PIC is thought to enhance the sinking of particulate organic carbon (POC) to deeper waters, potentially influencing the depth of organic matter remineralization and subsurface O2 levels. To explore these potential feedbacks, we examined the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved O2 in the Southeast Pacific open-ocean oxygen minimum zone – a region characterized by naturally low dissolved O2, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore abundance from late spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, were major contributors to PIC through the shedding of coccoliths. On average, about half of the PIC was attributed to reliably enumerated coccospheres and detached coccoliths, with significantly diminished pools below the euphotic zone. Temperature, O2, and pH emerged as key factors associated with PIC variability. PIC pools and PIC : POC ratios in both surface and subsurface waters in this naturally low-pH–low-O2 zone are lower than available data from most oceanic regions, with the exception of the Western Arctic. Our findings support the prediction that in upwelling regions with a shallow oxygen minimum zone, POC production is promoted by phytoplankton other than PIC-producing coccolithophores due to the injection of nutrient rich but low-pH water. This process decreases PIC : POC ratios, suggesting that the role of PIC in POC sedimentation might be decreased under such conditions. We emphasize that comparing PIC dynamics across diverse upwelling systems will be valuable for understanding how low-pH and low-O2 conditions influence POC fluxes mediated by coccolithophores.
Continue reading ‘Particulate inorganic carbon pools by coccolithophores in low-oxygen–low-pH waters off the Southeast Pacific margin’Temperature and CO2 alter trophic structure of Arctic plankton assemblages
Published 27 August 2025 Science ClosedTags: Arctic, biological response, BRcommunity, growth, laboratory, multiple factors, performance, phytoplankton, temperature, zooplankton
Driven by increasing anthropogenic CO2, the impact of ongoing climate change on the marine plankton ecosystem ultimately extends to higher trophic levels and the biogeochemical cycling of carbon and nutrients. However, the impacts of multiple environmental changes on trophic interactions between predator and prey have still not been fully explored. Here we conducted incubation experiments to determine the temperature and CO2 sensitivities of marine phytoplankton growth and microzooplankton grazing in the western Arctic Ocean, where rapid climate change is taking place. The temperature sensitivity of the growth of larger phytoplankton decreased owing to the increase in CO2 levels, whereas that of the growth of smaller phytoplankton increased under higher CO2 levels. Notably, the temperature sensitivity of Arctic phytoplankton is at least two times higher than the canonical estimates irrespective of size classes, highlighting the uniqueness of the Arctic ecosystem’s response to warming. Microzooplankton grazing was closely coupled with, but did not exceed, the growth rates of their prey, suggesting that microzooplankton behavior is mainly regulated by prey availability rather than the ambient environment. The higher competitiveness of smaller phytoplankton under higher temperatures and CO2 conditions might lead to a less productive Arctic Ocean ecosystem for higher trophic-level organisms in the future.
Continue reading ‘Temperature and CO2 alter trophic structure of Arctic plankton assemblages’Ocean acidification influences strain selection and metabolism of the benthic diatom Cocconeis neothumensis var. marina
Published 21 August 2025 Science ClosedTags: biological response, growth, laboratory, Mediterranean, physiology, phytoplankton, vents
The uptake of carbon dioxide (CO2) by oceans is dramatically altering the chemistry of seawater, leading to a continuous decrease of pH over the last century. This phenomenon, called ocean acidification (OA), has raised concerns due to its negative effects on marine biodiversity, including plankton communities and seagrass meadows. The most relevant seagrass in the Mediterranean is Posidonia oceanica, producing complex and stable benthic ecosystems. OA markedly affects the colonization and settlement patterns of epibionts within the leaf communities of P. oceanica. Epiphytic diatoms associated with P. oceanica are influenced by complex chemical and trophic interactions and play a fundamental role in the ecological successions characterizing the leaf stratum. In this study, we isolated two strains of Cocconeis neothumensis var. marina, one of the main epiphyte diatoms associated with P. oceanica, from two sites off the Island of Ischia (Italy) characterized by different pH conditions, i.e., a naturally low pH site (pH 7.6) influenced by volcanic CO2 emissions, and an adjacent location with ambient pH conditions (pH 8.1). We further cultured both strains of C. neothumensis under both pH conditions, resulting in four treatment conditions. Four significantly different growth curves were obtained, and metabolomic studies confirmed that the physiology of the strains differed according to pH conditions. Overall, this study demonstrated that OA is likely to trigger the selection of specific diatom strains, with possible consequences for trophic and chemical relationships among the associated consumers.
Continue reading ‘Ocean acidification influences strain selection and metabolism of the benthic diatom Cocconeis neothumensis var. marina’Ocean acidification and nitrate enrichment can mitigate negative effects of soft coral (Xenia) competition on hard coral (Stylophora pistillata) endosymbionts
Published 21 August 2025 Science ClosedTags: biological response, BRcommunity, community composition, corals, growth, laboratory, multiple factors, nutrients, otherprocess, physiology, phytoplankton
The combination of ocean acidification (OA) and eutrophication can undermine the physiological performance of reef-building corals during competition for benthic space, leading to shifts towards non-accreting organisms like soft corals. We conducted a 28-day laboratory orthogonal experiment to test if acidification (950 µatm pCO2) and moderate to high nitrate enrichment (4 and 8 µmolL−1) negatively affect the hard coral Stylophora pistillata while physically competing with the soft coral Xenia spp. We measured photosynthetic efficiency (PE) in hard corals and growth rate, Symbiodiniaceae density, and chlorophyll-a concentration in both hard and soft corals as proxies for their condition and responses to competition. Competition with the soft coral reduced PE, Symbiodiniaceae and chlorophyll-a contents of S. pistillata, while acidification alone and coupled with nitrate enrichment mitigated endosymbiont responses. The growth and chlorophyll-a concentrations of Xenia spp. were decreased by competition, but the soft coral was consistently benefited under nitrate enrichment. These results highlight that competition alone has a stronger negative impact on hard corals than on soft corals. Our study provides experimental evidence on how OA and eutrophication interact and shape coral dynamics, an overlooked but urgent topic in predicting reef futures under environmental change.
Continue reading ‘Ocean acidification and nitrate enrichment can mitigate negative effects of soft coral (Xenia) competition on hard coral (Stylophora pistillata) endosymbionts’Quantifying evolutionary changes to temperature-CO2 growth response surfaces in Skeletonema marinoi after adaptation to extreme conditions
Published 19 August 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, multiple factors, otherprocess, phytoplankton, temperature
Global warming and ocean acidification are having an unprecedented impact on marine ecosystems, yet we do not yet know how phytoplankton will respond to simultaneous changes in multiple drivers. To better comprehend the combined impact of oceanic warming and acidification, we experimentally estimated how evolution shifted the temperature-CO2 growth response surfaces of two strains of Skeletonema marinoi that were each previously adapted to four different temperature × CO2 combinations. These adapted strains were then grown under a factorial combination of five temperatures and five CO2 concentrations to capture the temperature-CO2 response surfaces for their unacclimated growth rates. The development of the first complete temperature-CO2 response surfaces showed the optimal CO2 concentration for growth to be substantially higher than expected future CO2 levels (~6000 ppm). There was minimal variation in the optimal CO2 concentration across the tested temperatures, suggesting that temperature will have a greater influence on growth rates compared to enhanced CO2. Optimal temperature did not show a unimodal response to CO2, either due to the lack of acclimation or the highly efficient CO2 concentrating mechanisms, which diatoms (e.g. Skeletonema) can up-/downregulate depending on the CO2 conditions. We also found that both strains showed evidence of evolutionary shifts as a result of adaptation to temperature and CO2. The evolutionary response differed between strains, underscoring how genetic differences (perhaps related to historical regimes) can impact phytoplankton performance. Understanding how a dominant algal species responds to multiple drivers provides insight into real-world scenarios and helps construct theoretical predictions of environmental change.
Continue reading ‘Quantifying evolutionary changes to temperature-CO2 growth response surfaces in Skeletonema marinoi after adaptation to extreme conditions ‘Adaptive phenotypic evolution of Skeletonema costatum to ocean acidification and warming with trade-offs from a multi-year outdoor experiment
Published 11 August 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, mesocosms, multiple factors, otherprocess, photosynthesis, physiology, phytoplankton, temperature
Human-induced climate change is increasing variability in marine environments, significantly affecting marine organisms and ecosystems. While marine diatoms can adapt to ocean acidification and warming in stable laboratory settings, their responses to long-term environmental changes under natural variability remain unclear. To investigate this, we cultivated Skeletonema costatum in outdoor semi-continuous cultures for over 3 years, exposing them to fluctuating natural light and temperature that tracked the in situ sea surface temperatures. We simulated current and future ocean conditions through four treatments: ambient CO2 and temperature (LTLC), elevated CO2 (LTHC), elevated temperature (+4°C, HTLC) and combined increases (HTHC). After 1396 days, we assessed populations in two assay environments (20°C, 400 ppm CO2 and 24°C, 1000 ppm CO2) for adaptations in growth rate, pigment composition and photosynthesis. The HTLC-selected group showed the highest growth rates in the HTHC assay environment, while the LTLC-selected group grew fastest in the LTLC assay environment, indicating adaptive evolution. Furthermore, populations selected under elevated conditions exhibited lower fitness in LTLC environments, highlighting a trade-off and underscoring the complexity of evolutionary adaptation in marine diatoms. Understanding these mechanisms is crucial for predicting phytoplankton dynamics and their role in marine ecosystems, especially in response to climate change.
Continue reading ‘Adaptive phenotypic evolution of Skeletonema costatum to ocean acidification and warming with trade-offs from a multi-year outdoor experiment’
