Posts Tagged 'abundance'

Long-term coral responses to high CO2: insights from volcanic vents and semi-enclosed bays

Published 20 October 2026 Science Leave a Comment
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This chapter provides a comprehensive review of natural laboratories used to study the effects of ocean acidification (OA) on coral reefs, emphasizing volcanic CO2 vents and semi-enclosed bays. It examines key environmental conditions at these study sites and their implications for coral physiology, biodiversity, and reef resilience. Two prominent natural analogues are highlighted: the Shikine Island warm-temperate shallow CO2 vent system in Japan and the semi-enclosed lagoon of Bouraké in New Caledonia.

Shikine Island represents a unique high-latitude coral environment influenced by the Kuroshio Current. The island’s CO2 vents provide a natural setting to investigate the community level effects of ocean acidification and how elevated CO2 levels interact with ocean warming and influence coral tropicalization. Findings suggest that while some corals persist at high CO2 levels, biodiversity declines significantly, with sensitive species unable to establish stable populations. Corals growing in these conditions exhibit reduced calcification, and the community structure shifts toward simpler, lower-complexity ecosystems dominated by turf algae. These results indicate that ocean acidification may act as a constraint on the poleward expansion of tropical corals, counteracting warming-induced range shifts.

In contrast, the semi-enclosed lagoon of Bouraké experiences extreme environmental fluctuations in pH, oxygen, and temperature, providing a window into the multifactorial stressors coral reefs may face in the future. Despite prolonged exposure to acidified, hypoxic, and thermally variable waters, corals in Bouraké demonstrate remarkable resilience. The system harbors diverse coral assemblages, with species exhibiting metabolic adjustments, increased heterotrophy, and shifts in symbiotic algae communities. This site suggests that coral ecosystems can develop physiological adaptations that enhance their survival in extreme conditions, offering valuable insights into the potential for long-term acclimatization.

By comparing these two contrasting natural analogues, this chapter highlights the complex interplay between acidification, warming, and other environmental stressors on coral reefs. While both sites provide critical insights into the future of coral ecosystems, they also underscore the urgent need for continued research and conservation efforts to mitigate the effects of climate change on marine biodiversity.

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A key seawater acidification-enriched gut bacterium, Pseudoalteromonas carrageenovora P1, enhances growth performance, antioxidant status, and disease resistance in sea cucumbers under seawater acidification

Published 28 September 2026 Science Closed
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Highlights

  • First discovery of Pseudoalteromonas enrichment in A. japonicus gut under acidification.
  • The dominant strain P. carrageenovora P1 was successfully isolated.
  • P. carrageenovora P1 activates host antioxidant and immune pathways to bolster stress resilience.
  • P. carrageenovora P1 significantly enhances resistance to V. splendidus 21,915 infection in A. japonicus.

Abstract

The sea cucumber (Apostichopus japonicus) is a key mariculture species of high economic value in East Asia. However, Ocean acidification, resulting from the increased uptake of anthropogenic CO₂ by seawater, severely impairs its growth, survival, and reproductive performance, thereby threatening the sustainable development of this aquaculture industry. The gut microbiota play a critical role in host adaptation to environmental stress; however, their involvement in mediating A. japonicus responses to seawater acidification remains unclear. Therefore, this study first compared the gut microbial communities of juvenile and adult A. japonicus under acidified and ambient seawater conditions. The results showed that Pseudoalteromonas abundance was significantly enriched under seawater acidification, from which the dominant strain, Pseudoalteromonas carrageenovora P1, was screened and isolated. This strain, when supplied as a dietary supplement under seawater acidification, improved A. japonicus growth performance and intestinal morphology, activated the Keap1-Nrf2-ARE and NF-κB pathways, enhanced antioxidant capacity and immune function, and increased resistance against Vibrio splendidus 21915 infection. Moreover, P. carrageenovora P1 modulated gut microbial structure by promoting beneficial bacteria such as Lutibacter while suppressing potential pathogens, including Vibrio, thereby maintaining intestinal homeostasis under acidification stress. This study reveals the important value of the gut microbiota of A. japonicus in regulating environmental tolerance of benthic invertebrates, and also provides a scientific reference for stress resistance regulation and health maintenance in A. japonicus aquaculture under seawater acidification.

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Comparative responses of coastal Arabian sea plankton to different ocean acidification simulation methods

Published 16 September 2026 Science Closed
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Ocean acidification (OA) is expected to alter marine phytoplankton communities by modifying seawater carbonate chemistry, with important implications for marine food webs and biogeochemical cycling. In this study, we tested the hypothesis that comparable pH reductions achieved through different acidification methods generate distinct carbonate chemistry conditions and consequently different biological responses. A 5-day microcosm experiment was conducted using natural phytoplankton assemblages collected from the coastal Eastern Arabian Sea. OA was simulated by HCl addition (acid), CO2 enrichment (CO2), and acid–base manipulation. Changes in carbonate chemistry, nutrients, phytoplankton community composition, pigments, bacteria, microzooplankton, and organic carbon pools were monitored. As expected, the three manipulation methods produced significantly different carbonate chemistry conditions despite comparable pH reductions. Repeated-measures ANOVA and Tukey’s post hoc analyses confirmed significant treatment effects for pH, pCO2, DIC, HCO3−, CO32−, and total alkalinity. By Day 5, CO2 enrichment significantly increased total phytoplankton abundance and promoted microplankton dominance, driven by bloom-like proliferation of Thalassiosira sp., whereas picoplankton declined significantly. Conversely, pennate diatoms, cyanobacteria, dinoflagellates, and coccolithophores exhibited weak or negative responses. Concurrent changes in phosphate, nitrite, autotrophic bacteria, and microzooplankton indicated that nutrient availability, microbial recycling, and grazing interacted with carbonate chemistry to regulate phytoplankton succession. Our findings demonstrate that phytoplankton responses in the oligotrophic Eastern Arabian Sea are governed by the combined effects of carbonate chemistry, nutrient dynamics, and ecological interactions rather than pH alone.

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Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters

Published 27 April 2026 Science Closed
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Coccolithophores, as calcifying phytoplankton, play a critical role in the global carbon cycle by producing calcium carbonate (CaCO3) in the ocean through their calcitic coccoliths. Here we examine Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related species abundance and genetic diversity along the West Coast of North America from samples taken on the 2021 NOAA West Coast Ocean Acidification (WCOA21) cruise, along the margin from British Columbia, Canada, to San Diego, California, USA. Significant carbonate chemistry gradients were observed across 17 transects, mostly in the onshore-offshore and north-to-south direction. Abundance and morphometrics of Gephyrocapsa spp. was evaluated using real-time PCR of mitochondrial cytochrome c oxidase subunit 3 ( cox3 ) gene and by microscopy. Variation in PIC concentrations, G. huxleyi and related species abundance, and coccosphere thickness were found to be associated with the gradients in carbonate chemistry and nutrient concentrations (phosphate, nitrate, nitrite, ammonium) across stations sampled during the cruise. We identified 5 unique amplicon sequence variants (ASVs) of Gephyrocapsa spp. cox3 that systematically varied in relative abundance across the California Current System. Southern California locations had greater diversity in cox3 sequences than northerly locations. These analyses represent baselines for evaluation of the impacts of future environmental changes in coastal waters along this productive upwelling regime.

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Responses of reef fish populations to similar environmental changes across distant oceanic islands

Published 9 April 2026 Science Closed
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Oceanic islands are among the most remote and understudied regions of the planet, yet they harbour unique reef fish communities that are increasingly vulnerable to global environmental change. Because these islands are geographically isolated, their populations are often assumed to respond mainly to local environmental conditions. However, by analysing temporal patterns in oceanographic variables across two distant systems (3204 km apart) in the South Mid-Atlantic Ridge (both encompassed by marine protected areas—MPAs), we found that temporal alignment in environmental conditions was associated with coordinated shifts in counts of nine reef fish populations in each study area. Among the evaluated variables, pH emerged as the most influential factor. Despite the divergent responses among reef fishes, possibly reflecting differences in physiological plasticity, shared temporal patterns in pH appeared central to parallel population patterns observed across assemblages. Increases in sea surface height and chlorophyll-a played secondary roles, potentially benefiting some populations, although such effects may be transient. These results suggest that climate-driven convergence in environmental conditions can override geographic isolation, promoting similar biological responses that may reduce resilience and increase extinction risk. Given that both islands are legally protected, our findings highlight that even MPAs are not insulated from large-scale oceanographic stressors, underscoring the need for long-term monitoring and adaptative conservation strategies for remote reef systems.

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Resilient adults but vulnerable larvae: demographic pathways of chiton decline under ocean acidification

Published 26 March 2026 Science Closed
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Highlights

  • Natural CO₂ seep systems showed reduced intertidal chiton abundance.
  • Adult chitons showed resilience to acidification in field and lab experiments.
  • Larval survival and recruitment were strongly impaired under acidified seawater.
  • Population declines are linked to early life-stage vulnerability.
  • Loss of chitons may reduce grazing and bulldozing, reshaping intertidal communities.

Abstract

Ocean acidification (OA) is a major threat to marine calcifiers; however, the sensitivity across taxa and life stages remains elusive. In this study, we combined field surveys of natural CO₂ seeps with laboratory exposure, transplantation, and larval settlement experiments to assess the effect of OA on chitons, a group of calcifying grazers and bulldozers that play critical roles in the structure of rocky intertidal ecosystems. Field surveys revealed approximately 98.6% reduction in chiton (Acanthopleura loochooana, Liolophura japonica, and Acanthochitona rubrolineata) abundance at acidified habitats (pH 7.6), despite greater microalgal food availability and no detectable increase in predator abundance. Laboratory CO₂-exposure experiments showed no direct effect of OA on adult A. loochooana survival, which is consistent with the presence of protective structural features in the valves that confer resistance to dissolution. Transplant experiments revealed no evidence of increased adult A. loochooana mortality in the acidified habitats (pH 7.6). In contrast, larvae showed pronounced sensitivity to OA, with acidified seawater (pH 7.6) reducing larval settlement by approximately 81.5% compared to control conditions (pH 8.1); early life stages were the most vulnerable. These findings suggest that OA-associated decline in chiton abundance is mainly mediated by impaired recruitment rather than by direct adult mortality, predation, or food limitation. Given the role of chitons as grazers and bulldozers, their loss could substantially change intertidal community dynamics by decreasing grazing pressure and disturbing algal and microbial assemblages. Our findings underscore the criticality of considering life-stage vulnerability and ecological function when evaluating the ecosystem-level consequences of OA.

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Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification on the coast of Korea

Published 25 March 2026 Science Closed
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This study aimed to investigate the meiofauna community characteristics in coastal waters affected by ocean acidification. Therefore, the meiofauna communities in the coastal waters of Hupo in Uljin-gun, which showed a high ocean acidification trend in the integrated data on the coastal areas of South Korea for the previous ten years, were monitored over five years. During the study period, the mean abundance of total meiofauna communities expressed in population density was 614 individuals (Inds.)/10 cm2. The most dominant taxa were nematodes (65–70%) and harpacticoids (7–20%); these two taxa accounted for approximately 80% of the total meiofauna abundance. Station (St.) 5 and 10, which had the lowest seawater pH values, showed the lowest average abundance values for harpacticoids (average 46 Inds./10 cm2) and nauplius (average 4 Inds./10 cm2) among the major meiofaunal groups over the 5-year period. In addition, St. 5 indicated the lowest meiofaunal diversity index of 0.54. To examine the effect of ocean acidification on meiofauna communities at the species level, species of nematodes, the most dominant taxon, were analyzed. The results indicated that the number of nematode species at St. 10, one of the two stations with the lowest pH, was the lowest compared to those at other stations. Analysis of c-p values for nematode species ​​showed that both species sensitive to environmental disturbance and species resistant to environmental pollution appeared at high rates. According to the feeding type of nematodes, epistrate feeders accounted for a remarkably high proportion at St. 10. This study provides various data on meiofauna community characteristics to understand the effects of ocean acidification on coastal ecosystems.

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Environmental controls and nonlinear responses of the diatom-dinoflagellate ratio in Jiaozhou Bay

Published 13 March 2026 Science Closed
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Highlights

  • Dia/dino abundance, biomass, and diversity ratios exhibited similar temporal patterns;
  • All ratios showed considerable heterogeneity without a consistent distributional trend;
  • Dia/dino ratios responded distinctly to DO, nutrients, and their interactions;
  • Shifting seawater properties exerted large influence on diatom-dinoflagellate dynamics.

Abstract

Diatoms and dinoflagellates are widely recognized as key indicators of marine ecosystem status and play central roles in ecosystem functioning and biogeochemical cycling. Yet how these two major phytoplankton groups adjust to changing coastal environments, and whether such adjustments occur coherently in different ecological dimensions, remains poorly constrained. Hence, we studied the temporal and spatial dynamics of diatom-dinoflagellate (dia/dino) ratios in Jiaozhou Bay during 2021 and 2024, integrating abundance-, carbon biomass-, diversity-, and richness-based metrics. Although abundance, biomass, and diversity ratios exhibited broadly similar temporal trajectories, the richness ratio displayed an opposite pattern, highlighting a decoupling between numerical dominance and species composition. Spatially, all four ratios exhibited significant heterogeneity, without a consistent nearshore-offshore gradient, reflecting complex local regulation. Correlation analyses revealed distinct controls on dia/dino ratios. The abundance ratio increased under conditions of elevated dissolved inorganic nitrogen (DIN) and reduced dissolved oxygen (DO), whereas the diversity ratio was associated with high DIN and low dissolved inorganic phosphorus (DIP). In contrast, the carbon biomass ratio was primarily linked to reduced DO and lower pH, while the richness ratio responded most strongly to the combined influence of low DO and elevated DIP. These contrasting responses indicated that dia/dino ratios captured different facets of phytoplankton community reorganization rather than reflecting a single environmental driver. Overall, our results suggested that the balance between diatoms and dinoflagellates in Jiaozhou Bay emerged from the coupled and nonlinear interactions among nutrient availability and oxygen dynamics. This study highlighted the dia/dino balance as an integrative indicator of coastal ecosystem condition and implied the importance of considering multiple ecological dimensions when assessing phytoplankton responses to ongoing eutrophication and environmental change.

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Ocean acidification reduces diatom and photosynthetic gene abundance on plastic in an coastal bay mesocosm experiment

Published 25 February 2026 Science Closed
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Discarded plastics are accumulating in the global ocean and posing threat to marine life. The plastisphere – the community colonizing plastic surfaces – profoundly influences plastic’s environmental behavior, affecting its degradation and entry into marine food webs. Ocean acidification (OA) resulted from anthropogenic CO2 emissions, is also threatening marine ecosystems, but the effect of OA on the structure and ecological function of the plastisphere community remains poorly understood. Here, using a mesocosm experiment, we investigated the effects of OA on the plastisphere colonizing floating PET plastic bottles. The study was conducted using subtropical eutrophic coastal water from Southern China under two CO2 conditions: increased CO2 to 1000 μatm (HC) and ambient CO2 410 μatm (LC). Metagenomic sequencing of the plastic samples, after exposure for 32 days, showed striking changes in relative abundance of eukaryotes and bacteria caused by HC. There was a 75.3 % decrease in eukaryote read abundances at high CO2, most strikingly a 95.6% decrease in the relative abundance of diatoms. In addition, the relative abundance of genes involved in photosystem II light reactions and pigment synthesis decreased under high CO2 conditions. This suggests that OA could reduce the photosynthetic potential within the plastisphere. Shifts in plastisphere community structure and potentially diminished photosynthesis under OA could influence the food chains within plastisphere, plastic degradation, transportation, and carbon cycle involving plastics. Overall, our results suggest that OA can alter the functional ecology of the plastisphere, with potential implications for marine biogeochemical processes and food web dynamics in subtropical eutrophic coastal water.

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Indo-Pacific coral reef sponge diversity declines under predicted future ocean conditions

Published 19 February 2026 Science Closed
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Future oceans are predicted to favor groups like sponges over calcifying taxa such as scleractinian corals. Here, we test this hypothesis by examining the development of coral reef communities in experimental mesocosms over 23 months. 85 sponge species among the calcifying class Calcarea (~33%), and non-calcifying Demospongiae (~60%) and Homoscleromorpha (<10%) recruited to warming (+2°C), acidification (-0.2 pH), and warming+acidification (+2°C, -0.2 pH) future ocean treatments. The diversity of calcifying sponges was unimpacted across any treatment, whereas non-calcifying classes showed greatest declines. 57-66% of demosponges decreased under future ocean conditions, and homoscleromorphs were entirely absent from acidified treatments. Through the sponge loop, sponges play a fundamental role in coral reef nutrient cycling, and altered coral reef community composition likely has functional consequences. This study challenges the assumption that non-calcifying species are less impacted and highlights the importance of understanding how community composition may alter ecosystem functioning under future ocean conditions.

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Acute microbial and nutrient responses to elevated temperature and pCO2: a coastal UK microcosm study

Published 13 February 2026 Science Closed
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The coastal ocean’s ecosystem resilience is consistently hampered by the compounding impacts of projected climate change and anthropogenic perturbation. In this microcosm study, we investigated how elevated temperature and pCO2, together with episodic nutrient pollution and a short-term marine heatwave, affect the nano- and picoplanktonic community of primary producers and subsequent changes in coastal biogeochemistry. Our study demonstrates that future elevated temperature and pCO2 conditions impact the planktonic community, first by a ∼ 50 % decreased autotrophic abundance, and second by a shift from larger eukaryotic to smaller cells. When combined with a heatwave, total primary producers experienced an additional 37–38 % decrease, indicative of a negative synergistic effect beyond either stressor alone. Picoeukaryotes were particularly sensitive, declining by 44–50 %. Short-term nutrient pollution under ambient conditions induced a 41 % increase in cell abundance, but failed to stimulate biomass under elevated temperature and pCO2, and instead led to altered organic matter dynamics, including significantly lower carbon fixation. These findings emphasize the need for further evaluation of multi-stressor interactions to better understand biogeochemical vulnerability, nutrient retention, and ecological functioning in coastal ecosystems undergoing rapid climatic and anthropogenic change.

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Microbial community dynamics over large spatial and environmental gradients in a subtropical ocean basin

Published 9 February 2026 Science Closed
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Microbes are fundamental to ocean ecosystem function, yet they remain understudied across broad spatial and environmental scales in dynamic regions like the Gulf of America/Gulf of Mexico (GOM). We employed DNA metabarcoding to characterize prokaryotes (16S V4–V5) and protists (18S V9) across 51 stations, spanning 16 inshore–offshore transects and three depths. Cluster analysis revealed three clusters corresponding to depth zones that integrated vertical and horizontal sampling: photic zone (inshore near surface–bottom and offshore surface), deep chlorophyll maximum (offshore), and aphotic zone (offshore near bottom). We applied group-specific generalized additive models (GAMs) to log-transformed abundance data of major taxa in the photic zone, identifying key environmental factors that explained 42%–82% of the variation in abundance. SAR11 and SAR86 were positively associated with temperature and dissolved inorganic carbon, while cyanobacterial genera (Prochlorococcus and Synechococcus) were differently impacted by nutrients, salinity, and pH in ways that often followed their expected ecological niches. Representatives of protist parasites (Syndiniales) and grazers (Sagenista) showed group-specific nonlinear associations with salinity, oxygen, nutrients, and temperature. Using GAMs, we expanded the spatial resolution of DNA sampling and predicted surface log abundances at 84 cruise sites lacking amplicon data. Indicator analysis was performed with sequence-level data, revealing several protists that were indicative of more acidic waters and the absence of any significant prokaryote indicators. Our results provide the first basin-scale survey of microbes in the GOM and highlight the need for coordinated omics and environmental sampling to improve predictions of microbial responses to changing conditions.

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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 Closed
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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.

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Newly discovered CO2 (carbon dioxide) vent cave drives r-strategy shift in a Mediterranean aphotoendosymbiotic coral

Published 14 November 2025 Science Closed
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Highlights

  • Characterization of an unexplored CO2 vent cave
  • CO2 vents chemical-physical parameters affect ecological traits of calcifiers
  • Aphotoendosymbiotic solitary coral naturally inhabiting a CO2-rich gas environment.
  • Prolonged acidified conditions did not affect C. inornata growth rate
  • Shift towards an r-demographic strategy in response to acidified conditions

Abstract

Submarine CO2 volcanic vents represent peculiar environments with varying seawater chemical-physical parameters that may affect the ecological traits of calcifying organisms, such as growth and demographic characteristics. The present study focused on exploring the growth and population dynamics of a temperate, solitary and aphotoendosymbiotic coral Caryophyllia inornata (Duncan, 1878) living in a CO2 vent cave at 14 m depth. The volcanic emissions in and around the cave led high levels of pCO2, resulting in lower calcium carbonate saturation state (Ωa: 2.1–2.2) values compared to those observed in the ambient seawater of the Mediterranean Sea, not affected by venting activity. Prolonged acidified conditions (pHT: 7.5) did not affect C. inornata growth rate but resulted in a population with higher percentage of juvenile individuals, lower average ages and a lower age at maximum biomass percentage, thus suggesting a transition in its population dynamics towards an r-demographic strategy. This study provides a detailed characterization of a previously unexplored CO2 vent cave, highlighting the importance of these sites as natural laboratories to offer valuable insights into understanding the full ecological impact of aphotoendosymbiotic corals under ocean acidification.

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Depth-resolved vertical distribution of the pteropod Limacina helicina in the Northeast Pacific and its implications for exposure to ocean acidification

Published 27 October 2025 Science Closed
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The pteropod Limacina helicina has become an important bioindicator for the impacts of ocean acidification on marine ecosystems, yet its vertical distribution and diel vertical migration (DVM) patterns remain poorly understood. Understanding these behaviours is critical to accurately predict the risks of ocean acidification to pteropods since the depth ranges they inhabit strongly influence their exposure to water corrosive to aragonite shells (i.e. ΩAr⁠ <1), given the natural vertical gradients in pH and ΩAr⁠. To resolve the vertical distribution of L. helicina, we utilized an existing dataset consisting of 179 vertically stratified zooplankton net tows from the Northeast Pacific spanning 1983–2019. Using conventional observational analyses and Bayesian statistical models, we determine and compare the average day and night vertical distributions of two size ranges of L. helicina, plus those of the strong vertical migrator euphausiid Euphausia pacifica and a non-migratory control group of mollusc larvae. We show that the average day and night vertical distributions and mean depths of L. helicina do not differ and closely match those of the non-migratory control, indicating that L. helicina does not perform DVM in this region. Typical mean depths of L. helicina are ∼50–70 m, with ≥ 75% of the population occupying the upper ∼100 m, and ≥ 50% being found in the upper ∼50 m, regardless of body size and time of day. Given the typical shape of ΩAr profiles in the ocean, we estimate that pteropod exposure to low ΩAr may be overestimated if calculated using the standard vertically integrated approach (i.e. a homogeneous depth distribution) as opposed to our depth-resolved vertical distribution.

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Significant effects of temperature and pH on zooplankton dynamics: implications for ocean warming and acidification

Published 20 October 2025 Science Closed
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Highlights

  • The Yellow Sea coast showed a trend of warming and acidification of the sea water.
  • Zooplankton along the Yellow Sea coast were affected by temperature and pH.
  • Zooplankton showed significant spatial and temporal dynamics.

Abstract

Coastal ecosystems are increasingly affected by ocean warming and acidification, yet their combined impacts on zooplankton communities remain inadequately studied. Based on 11 ecological surveys conducted along the Yellow Sea coast between 2021 and 2023, we analyzed the responses of zooplankton communities to changes in seawater temperature and pH, which were accompanied by pronounced seasonal and spatial variation in community structure. Results revealed continuous warming and acidification trends. Copepods were the dominant group, followed by planktonic larvae, while Noctiluca scintillans and Centropages abdominalis exhibited clear seasonal outbreaks. Temperature showed a significantly negatively correlated with zooplankton abundance and biomass but positively with diversity and evenness, conversely, pH demonstrated the reverse pattern. Model analyses further indicated that the synergistic effects of warming and acidification were a major driver of dynamic and nonlinear fluctuations in zooplankton communities, pointing to the ecological instability of this coastal ecosystem. These findings provide observational evidence of climate-driven ecological change and highlight the importance of integrating zooplankton indicators into coastal monitoring and management strategies.

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The effects of ocean acidification on the epiphytic bacterial community of Sargassum thunbergii via high-throughput sequencing

Published 11 September 2025 Science Closed
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Marine macroalgae and their epiphytic bacteria have established a symbiotic relationship. Although the effects of ocean acidification (OA) on macroalgae have been extensively studied, its impact on these epiphytic bacteria remains unclear. This study investigated the OA-induced shifts in the epiphytic bacterial community of Sargassum thunbergii from Qingdao’s intertidal zone using 16S rDNA sequencing. The results indicated that elevated CO2 altered bacterial community structure and function, reducing diversity while maintaining dominant taxa but significantly changing their relative abundances. The abundances of Proteobacteria, Firmicutes, and Verrucomicrobiota declined, whereas Campylobacterota, Desulfobacterota, and Spirochaetota increased. The specific phyla like Cloacimonadota, Calditrichota and Entotheonellaeota also emerged. These shifts were linked to the environmental adaptability and stress resistance of epiphytic bacteria as well as the metabolic activities of the host algae, particularly in protein and fatty acid degradation.

Functional predictions revealed that OA primarily affected nitrogen and sulfur metabolism in the epiphytic bacterial community, with effects intensifying over time. Specifically, nitrogen fixation increased, while dark oxidation of sulfur compounds, dark sulfite oxidation, and dark sulfur oxidation decreased. In conclusion, ocean acidification directly induced changes in the abundance of epiphytic bacterial taxa with varying stress resistance and adaptability. Simultaneously, it promoted shifts in bacterial taxa closely associated with the host algal metabolic activities, ultimately reshaping the epiphytic bacterial community on S. thunbergii. These findings provided new insights into the macroalgae-epiphytic bacteria interactions under ocean acidification and provided important guidance for macroalgal cultivation.

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Decreasing foraminiferal flux in response to ongoing climate change in the Santa Barbara Basin, California

Published 2 September 2025 Science Closed
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The rapid response of foraminiferal assemblages to changing climate makes their shells an invaluable geological record of the past. However, the time frame over which foraminifera respond to climatic signals and the specific drivers influencing assemblage composition and abundance remain obscure. We focus on the impact of ongoing, anthropogenic climate change on planktic foraminifera in the California Current ecosystem, which would appear as a nearly instantaneous event in the sediment record. The Santa Barbara Basin sediment trap, located off the coast of California, USA since 1993, provides a record of more than 30 years of particulate and foraminiferal flux in the basin. The sediment trap captures the superposition of the annual cycle of seasonal upwelling, Pacific multiannual El Niño–Southern Oscillation-driven temperature changes, and anthropogenically forced climate change. We present data on planktic foraminiferal flux collected between 2014–2021, at two-week intervals (164 samples, 60 006 individuals) and compare results to previously published data from 1993–1998. Consistent with previous studies, the most abundant species from 2014–2021 were Globigerina bulloides, Neogloboquadrina incompta, and Turborotalita quinqueloba, with peak fluxes occurring in the spring and summer. Lower fluxes and an increase in the abundance of N. incompta and subtropical species characterize the winter season. We find a 37.9 % decrease in total foraminiferal flux relative to the 1990s, primarily driven by a decrease in G. bulloides abundance. This decrease is accompanied by a 21.0 % overall reduction in calcium carbonate flux. We also find a decrease in the relative abundance of subtropical species (Globigerinoides ruber, Orbulina universa, and Neogloboquadrina dutertrei) and their fluxes compared to the 1990s, opposite expectations if assemblages and fluxes were to follow anthropogenic warming signals. We hypothesize that the observed decrease in subtropical species abundance and flux is likely related to an increase in acidification and in the timing and magnitude of upwelling along the California coast. The extremely rapid responses of foraminifera to ongoing changes in carbonate chemistry and temperature suggest that climate change is already having a meaningful impact on coastal carbon cycling. The observed decrease in particulate inorganic carbon (PIC) flux relative to particulate organic carbon (POC) flux may facilitate increased oceanic uptake of atmospheric CO2.

Continue reading ‘Decreasing foraminiferal flux in response to ongoing climate change in the Santa Barbara Basin, California’

Pteropods reliably record the aragonite compensation depth in the western Bay of Bengal

Published 21 August 2025 Science Closed
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Anthropogenic greenhouse gas emissions have a detrimental impact on the carbon sequestration by the oceans. Pteropods, a crucial component of the ocean’s planktic community, secrete aragonite shells that are sensitive to increasing atmospheric carbon dioxide levels, making them the first indicators of ocean acidification. Therefore, pteropods are often used to observe the changes in aragonite compensation depth (ACD). Intriguingly, in the major parts of the northern Indian Ocean, the chemically defined ACD is < 800 m, but pteropods have been reported in surface sediments collected from much deeper depths in the same region, which raises questions about the use of pteropods to trace ACD in this area. To address this ambiguity, we conducted a systematic and detailed evaluation of pteropods to trace the changes in ACD in the western Bay of Bengal, which is the first-ever such study. The pteropods population dominated by Heliconoides inflatus was low on the inner shelf, and isolated pockets of high pteropod abundance were restricted to the upper slope. Based on the pteropod abundance in the surface sediments and the ratio of pteropods to planktic foraminifera, we report the baseline ACD in the western Bay of Bengal at ~ 500 m. The aragonite compensation depth based on the pteropod abundance in the surface sediments correlates well with the chemically defined ACD in this region. These findings will help to assess the impact of ocean acidification on aragonite compensation depth in the western Bay of Bengal.

Continue reading ‘Pteropods reliably record the aragonite compensation depth in the western Bay of Bengal’

Interactive effects of ocean acidification and warming disrupt calcification and microbiome composition in bryozoans

Published 12 August 2025 Science Closed
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Marine habitat-forming species provide crucial ecosystem functions and services worldwide. Still, the individual and combined long-term effects of ocean acidification and warming on bryozoan populations, structures, and microbiomes remain unexplored. Here, we investigate the skeletal properties, microbiome shifts, and population trends of two bryozoan species living inside and outside a volcanic CO2 vent, a natural analog to future ocean acidification conditions. We show that bryozoans can acclimatize to acidification by adjusting skeletal properties and maintaining stable microbiomes. However, we document a decrease in microbial genera playing essential functions under acidified conditions. Moreover, we show that ocean acidification exacerbates bryozoan cover loss and mortality caused by ocean warming. The observed shifts in the microbiome and cover suggest that, despite their morphological plasticity, bryozoan species will be heavily impacted by future ocean conditions, posing a threat to many benthic ecosystems in which they play a pivotal role.

Continue reading ‘Interactive effects of ocean acidification and warming disrupt calcification and microbiome composition in bryozoans’

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