Posts Tagged 'community composition'

Ecological stability of late Maastrichtian benthic foraminifera amidst Deccan volcanism

Published 29 December 2025 Science Closed
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Highlights

  • Benthic foraminifera assemblage at Bidart reveal a stable, mesotrophic late Maastrichtian seafloor.
  • K/Pg boundary at Bidart shows signs of ecological stress and taphonomic dissolution.
  • Deccan-induced calcification stress was restricted to surface ocean and had minimal impact on benthic foraminifera.
  • Robust test ratio and fragmentation index together serve as effective taphonomic proxies.

Abstract

The late Maastrichtian witnessed profound disruptions in biogeochemical cycles, leading to the fifth mass extinction at the Cretaceous–Paleogene (K/Pg) boundary. At Bidart section (France), the final ∼60 kyr of the Maastrichtian coincide with mercury (Hg) peaks, low magnetic susceptibility, evidence of biological stress and taphonomic alteration in planktic foraminifera, indicative of an ocean acidification event. While this event primarily appears to be a surface-ocean phenomenon, previous studies also documented a minor rise in benthic foraminiferal test fragmentation beginning 0.5 m below the K/Pg boundary, with a pronounced spike at the boundary itself.

A detailed investigation of benthic foraminifera in biozone CF1 at Bidart section (France) reveals a diverse and balanced assemblage preceding the K/Pg boundary, with minimal taphonomic alterations. At the K/Pg boundary, infaunal populations diminished, diversity declined sharply, test fragmentation intensified, yet paradoxically, the absolute abundance of genera rose markedly. Preferential preservation is evident in the dominance of robust taxa (Cibicidoides spp., Coryphostoma spp.), while a high fragmentation index reflects strong taphonomic dissolution and time-averaging. A plausible explanation for this could be CO2-rich waters mixing into the ocean interior over 100–1,000 years, driving dissolution during the ∼10,000-year deposition of the K/Pg boundary red clay. The stark contrast between the planktic and benthic census and morphometric data at Bidart section clearly constrains any Deccan-related calcification stress to the surface mixed layer. Lastly, the integrated planktic and benthic considerations re-emphasize a need to carefully separate taphonomic signals from true ecological stress.

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Syntheses on taxonomic and functional biodiversity related to ocean acidification in a well-studied CO2 vents system: the Castello Aragonese of Ischia (Italy)

Published 22 December 2025 Science Closed
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Ocean acidification (OA) is considered a relevant additional threat to marine biodiversity and is linked to the increasing CO2 concentration in the atmosphere. Here, we provide a synthesis on the loss of both taxonomic and functional biodiversity, in the up to date best studied CO2 vents in the world, the Castello Aragonese of Ischia (Tyrrhenian Sea, Italy), analyzing a large data set available at this site and reporting qualitative taxonomic data along a gradient of OA from ambient normal conditions outside the vents (pH 8.1) to low pH conditions (pH 7.8–7.9) and extreme low pH conditions (pH < 7.4). A total of 618 taxa were recorded (micro- and macrophytes, benthic invertebrates, and fishes). A relevant loss of biodiversity (46% of the species) was documented from control/normal pH conditions to low pH, and up to 56% species loss from control of extreme low pH conditions. Functional groups analysis on the fauna (calcification, size, motility, feeding habit, and reproduction/development) allowed us to draw an identikit of the species which is able to better thrive under OA conditions. These are motile forms, small- or medium-sized, generalist feeders, at the low level of the food web (herbivores or detritivores), mainly brooders, or with indirect benthic development, and without calcification or weakly calcified.

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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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Progressive changes in coral reef communities with increasing ocean acidification

Published 8 December 2025 Science Closed
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Ocean acidification from increasing atmospheric CO2 is progressively affecting seawater chemistry, but predicting ongoing and near-future consequences for marine ecosystems is challenging without empirical field data. Here we quantify tropical coral reef benthic communities at 37 stations with varying exposure to submarine volcanic CO2 seeping, and determine the aragonite saturation state (ΩAr) where significant changes occur in situ. With declining ΩAr, reef communities displayed progressive retractions of most reef-building taxa and a proliferation in the biomass and cover of non-calcareous brown and red algae, without clear tipping points. The percent cover of all complex habitat-forming corals, crustose coralline algae (CCA) and articulate coralline Rhodophyta declined by over 50% as ΩAr levels declined from present-day to 2, and importantly, the cover of some of these groups was already significantly altered at an ΩAr of 3.2. The diversity of adult and juvenile coral also rapidly declined. We further quantitatively predict coral reef community metrics for the year 2100 for a range of emissions scenarios, especially shared socio-economic pathways SSP2-4.5 and SSP3-7.0. The response curves show that due to ocean acidification alone, reef states will directly depend on CO2 emissions, with higher emissions causing larger deviations from the reefs of today.

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Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea

Published 5 December 2025 Science Closed
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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.

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Impact of ocean acidification on the intestinal microflora of Sinonovacula constricta

Published 20 November 2025 Science Closed
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The intestinal microflora, which is vital for nutrient absorption and immune regulation, can experience dysbiosis under environmental stress, potentially enhancing host susceptibility to pathogenic invasion. The impact of ocean acidification on bivalves is substantial, but its effects on their intestinal microflora remain poorly understood. To explore the impact of ocean acidification on the intestinal microflora of Sinonovacula constricta, this study used high-throughput 16S rRNA sequencing technology to investigate the variations in the intestinal microflora communities of S. constricta during ocean acidification across different time points. After exposure to ocean acidification, changes in the composition of the intestinal microflora of S. constricta were observed, with no significant difference in α-diversity between the acidified and control groups. The abundance of Proteobacteria in the acidification group increased, whereas that of Cyanobacteria decreased. The abundance of Firmicutes initially decreased and then increased. At the genus level, the relative abundance of Pseudomonas was lower than that in the control group, whereas the relative abundance of Photobacterium, Acinetobacter, and Enterobacter gradually increased. LEfSe analysis identified Serpens as the discriminative biomarker at 7 days of acidification, Enterobacteriales, Rhodobacteraceae, and Martvita at 14 days of acidification, and Serpens, Acidibacteria, and Aeromonadaceae at 35 days of acidification. Functional prediction analysis indicated significant stimulation in various metabolic pathways at different time points following acidification stress. Specifically, pathways involved in biosynthesis were significantly stimulated at 14 days of acidification, while those related to sucrose degradation were disrupted at 35 days. The results further indicated that ocean acidification stress can influence the intestinal microflora of S. constricta, but no severe dysbiosis or digestive system impairment was observed at the microbial level. This study provides new insights into the effects of ocean acidification on the intestinal microflora of marine bivalves.

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Sediment topography enhances the response of coral reef carbonate sediment dissolution to ocean acidification

Published 13 November 2025 Science Closed
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The interaction between water flow and sediment topography (e.g., surface ripples) in shallow, permeable coral reef carbonate sediments establishes pressure gradients that increase the rate of sediment–water solute exchange relative to water flow along a flat bottom. It is unknown how this effect from surface ripples may modify the rate at which the sediment porewater is exposed to future chemical changes in the overlying water column, such as elevated pCO2 that is causing ocean acidification (OA). To address this question, this study used a series of 22-h incubations in flume aquaria with live permeable calcium carbonate sediment communities and examined the interactive effect of pCO2 (400 and 1000 µatm) and surface topography (flat and rippled sediments) on invertebrate infaunal activity, carbonate sediment microbial metabolism, and inorganic carbonate dissolution. Results show that the introduction of oxygen into flat sediments was largely driven by infaunal activity, whereas introduction of oxygen into rippled sediments was largely driven by physical flow processes. Rippled sediments exhibited rates of respiration and gross primary production that were ~ 45% and ~ 50% higher, respectively, than flat sediments. An increase in pCO2 shifted the sediments in the flat flumes from net calcifying to net dissolving, an effect that was amplified an additional ~ 60% in rippled sediments. These results suggest that current estimates of coral reef carbonate sediment calcification may be underestimating the dissolution response to OA where the carbonate sediment environment exhibits ripples in the topography.

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Biogeochemical properties of shallow-water CO2 seeps on Himeshima Island and Showa Iwojima Island, Japan

Published 7 November 2025 Science Closed
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Volcanic gases erupt from the seafloor in several regions around Japan. Volcanological and geochemical gas seep studies have mainly focused on coastal shallow-water areas that are relatively accessible and important to human society. Shallow-water CO2 seeps are thought to foreshadow future marine environments that may develop if CO2 emissions are not drastically reduced. Thus, CO2 seeps provide important insights for assessing and projecting the impacts of ocean acidification on marine ecosystems. This study is the first to investigate two shallow-water CO2 seeps near Japan from the perspective of ocean acidification. We observed biotic transitions and reduced biodiversity around these CO2 seeps, as well as high CO2 concentrations, low pH, and low calcium carbonate saturation—conditions expected to occur by the end of this century unless anthropogenic CO2 emissions are significantly reduced. These results suggest that, from a marine life conservation perspective, it is essential to mitigate ocean acidification through substantial reductions in anthropogenic CO2. Shallow-water CO2 seeps serve as natural experimental sites that illustrate ocean acidification and its effects on marine ecosystems. Given that the shallow-water CO2 seeps examined in this study are both located in geoparks, study tours and ecotourism field trips should utilize these sites to enhance awareness of the consequences of ocean acidification and climate change.

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Elevated carbon dioxide does not increase macroalgal community photosynthesis

Published 4 November 2025 Science Closed
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Ocean acidification, driven by rising atmospheric carbon dioxide levels, has impacts on marine ecosystems. While elevated carbon dioxide concentrations have the potential to enhance Blue Carbon fixation and storage, the response of community photosynthesis in macroalgal-dominated ecosystems remains poorly understood. Here, we investigated the effects of elevated carbon dioxide on macroalgal communities using volcanic carbon dioxide vents as a natural analogue of ocean acidification. Net community photosynthesis was assessed using chambers positioned on the seafloor as well as water mass dynamics monitoring. Despite a shift in algal community composition, only minimal differences in net community photosynthesis were observed between reference and high carbon dioxide sites. The high carbon dioxide site had a lower abundance of algal species with carbon dioxide concentrating mechanisms, based on δ13C isotope measurements. Carbon dioxide concentrating mechanisms facilitate photosynthesis under present-day levels of carbon dioxide in seawater, resulting in a negligible effect of elevated carbon dioxide on macroalgal community photosynthesis. These results challenge the assumption that ocean acidification will enhance Blue Carbon uptake and storage, necessitating a reevaluation of this perspective.

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Gut microbial community plasticity as a climate shield mediating sea cucumber resilience to ocean acidification and warming

Published 28 October 2025 Science Closed
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Ocean acidification (OA) and ocean warming (OW) pose escalating threats to marine ecosystems, particularly to benthic organisms, such as sea cucumbers, that play pivotal roles in nutrient cycling and sediment health. Existing studies have mostly focused on the physiological responses of sea cucumbers, yet overlooked the critical roles of both gut microbial communities and metabolites in the host’s responses under environmental stress. Herein, a mesocosm experiment was constructed and analyzed by using integrated gut microbiome and metabolomics approaches to investigate the responses of sea cucumbers Apostichopus japonicus to OA and OW. Results revealed that microbial community plasticity underpins holobiont adaptation, with warming restructuring gut microbiota toward thermotolerant taxa, whereas acidification enriches alkalinity-modulating Rhodobacteraceae and Halioglobus sp.. Metabolomic profiling identified 43 amino acid derivatives that exhibit significantly increased concentrations in the OA and OW groups. These derivatives include upregulated N-methyl-aspartic acid and γ-glutamyl peptides, which stabilize macromolecules and enhance redox homeostasis. Conversely, antioxidative metabolites, such as ergothioneine and L-homocystine, are suppressed, reflecting trade-offs between energy allocation and stress protection. In OW group, the antioxidant synthesis pathway is shifted to energy metabolism related to heat tolerance, whereas in OA group, energy is preferentially used for alkalinity regulation pathways rather than oxidative stress defense. Changes in microbial community structure mechanistically explain the trends in metabolite concentrations, as the proliferation of Vibrio spp. in the OW group drives lysine catabolism, leading to a significant increase in L-saccharopine levels. The reduction of Bacteroidetes in the OA group is correlated with the downregulation of L-homocystine, suggesting that pH-driven microbial interactions are disrupted. These findings demonstrate that gut microbiota reconfigure community structure and metabolic landscapes to buffer hosts against climate stress synergies, highlighting the importance of microbiome-mediated resilience in marine ecosystems under global climate change.

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Seasonal and interannual variability of Atlantidae heteropods along the west coast of Baja California, Mexico

Published 23 October 2025 Science Closed
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Highlights

  • Atlantid species richness was higher in winter than in spring.
  • Maximum species diversity was associated with the 2013–2016 anomalous warm period.
  • Distribution associated with seawater masses, hypoxia, and aragonite saturation.
  • Atlantid species are potential biological indicators of environmental changes.

Abstract

The Atlantidae are holoplanktonic gastropods with aragonitic shells that inhabit the epipelagic habitat primarily in tropical and subtropical oceans, as well as in certain transitional and temperate regions, such as the California Current System. However, there is limited knowledge about how their diversity, distribution, and abundance respond to environmental changes over different time scales. The strongest seasonal changes of zooplankton species composition and environmental conditions in the southern California Current System occur between winter and spring. El Niño Southern Oscillation and marine heat waves are two additional environmental change drivers of interannual scale. Our aim was to infer the effect of the seasonal (winter-spring) and interannual (2012–2016) environmental variability on the diversity, distribution, and abundance of the Atlantidae species assemblage along the Pacific coast off the Baja California peninsula, Mexico. Atlantidae diversity was higher during winters than during springs. Their horizontal distribution recorded during winter was statistically correlated with temperature, salinity, and the seawater masses distribution, and during spring was correlated with the depth of hypoxic conditions (<60 μmol O2/kg oxyline) and the depth of Ω aragonite saturation horizon. Atlanta californiensis was the most abundant species, mainly during spring and its relative abundance decreased during anomalously warm periods, while tropical/subtropical species showed an opposite abundance pattern. The maximum species richness was associated with the 2013–2015 marine heat wave and El Niño 2015–2016 events, when tropical species were observed in the study area. Differences in the species community structure, their response to Ω aragonite undersaturated waters and hypoxia, and their seawater mass affinity showed that atlantids are useful biological indicators of environmental changes, ocean acidification, and deoxygenation conditions.

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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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Coupled acidification-nitrification dynamics in eutrophic estuarine waters

Published 20 October 2025 Science Closed
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Highlights

  • Mid-estuary emerges as a hotspot for coupled acidification-nitrification, intensified by hydrology.
  • Nitrifier community structure adapts to acidification stress, while responds differently.
  • AOB is more sensitive to acidification in estuarine water compared to AOA.
  • Future climate change scenarios project intensified acidification and nitrification coupling in mid-estuary.

Abstract

The interplay between acidification and nitrification in estuarine systems could have profound effects on coastal biogeochemistry and ecosystem health. However, the lack of integrated field research risks oversimplifying their relationships in complex ecosystem dynamics. This study investigates the spatiotemporal covariations of acidification sensitivity and nitrification rates derived from observed inorganic carbon and nutrients data along a land-sea continuum. In the middle estuary, estuarine pH exhibited the highest sensitivity to ammonium concentration, coinciding with maximum nitrification rates. The coupling effect intensified by 40% during the transition from dry to wet hydrological conditions. Despite that microbial network complexity generally decreased with increased acidification sensitivity, ammonia-oxidizing bacterial communities are more sensitive to acidification in estuarine water compared to ammonia-oxidizing archaea. Conversely, in the lower estuary, acidification was associated with a decline in nitrification activities. Machine learning-based models suggest that climate change scenarios could exacerbate acidification and nitrification in the Pearl River Estuary, potentially amplifying their coupling effect in the middle estuary. This holistic approach not only advances our fundamental understanding of estuarine processes, also provides critical insights for policymakers and coastal managers striving to maintain the ecological integrity of these vital ecosystems in an era of rapid global change.

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The bacterial community composition of American lobster (Homarus americanus) embryos and recently hatched larvae held under different temperature and acidification conditions

Published 16 October 2025 Science Closed
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Previous research investigating the microbial community of American lobster embryos has long led researchers to believe this habitat comprised only a select few bacterial taxa. However, using 16S rRNA gene sequencing, we show this community to be more diverse than previously thought. We investigated how the bacterial communities of American lobster embryos and larvae change over embryogenesis and hatching in response to two environmental variables. Ovigerous female lobsters caught from Maine and Massachusetts were held under varying temperature and pH regimes that approximated observed and predicted warming and ocean acidification conditions in the Gulf of Maine (GoM) and Southern New England (SNE). The bacterial microbiome associated with the lobster embryos was quantified from two-time points during the experiment, and larvae were collected within 12 hours of hatching. Alpha diversity increased with each life history stage, and embryo and larvae microbiomes shared little community overlap with that in the surrounding tank water. Neither environmental conditions nor lobster origin significantly altered bacterial communities, with life history stage driving alpha and beta diversity. Embryos and larvae shared three core bacterial members identified as members of the genera Rubritalea, Delftia, and Stenotrophomonas. American lobster embryos and larvae appear to have a highly selective microhabitat for bacteria that is not altered by environmental conditions. This leads us to wonder what role the microbiome may have on a developing lobster, and where the microbiome is originating if not from the surrounding seawater.

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Environmental conditions and carbonate chemistry variability influencing coral reef composition along the Pacific coast of Costa Rica

Published 10 October 2025 Science Closed
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Coral reef development is influenced by a wide variety of factors, including temperature, salinity, nutrient concentrations, and carbonate chemistry. Studies focusing on physicochemical drivers of coral reef distribution and composition in the Eastern Tropical Pacific (ETP) are scarce, and carbonate chemistry and nutrient data for this region are limited. This study measured coral reef composition and physicochemical parameters along the Pacific coast of Costa Rica, over a one-year period at three locations: Santa Elena and Matapalo in the north, and Parque Nacional Marino Ballena in the south. Our results show high seasonal and spatial variability of physicochemical conditions with significant differences mainly explained by inorganic nutrient concentrations, with driving processes also having a strong influence on the variability of carbonate chemistry parameters. Coastal upwelling is the main driver of the seasonal variability in Santa Elena. Comparison of seasonal dissimilarity within locations confirms the presence of a geographical gradient, with stronger influence of the upwelling in Santa Elena relative to Matapalo, where several parameters displayed a lower seasonality and a carbonate system that supports reef development throughout the year. Conversely, in Marino Ballena the river discharges during rainy season exerted a strong control on the seasonal variability. The integrated analysis of coral reef composition and physicochemical parameters suggests that in addition to inorganic nutrients carbonate chemistry also plays a key role in coral distribution. Analyzing the spatial distribution of the main reef builders provides insights into the species-specific tolerance to varying conditions. Pavona clavus is widely distributed in both the northern and southern locations, suggesting that this massive coral is very tolerant to the high variability of physicochemical conditions. The dominant corals in the north (Pavona gigantea and Pocillopora spp.) are highly tolerant to nutrient-enriched cold waters with low aragonite saturation, while one of the main reef-builders in southern locations (Porites cf. lobata) cope better with low salinity, low aragonite saturation and low light intensity caused by river discharges. Understanding the preferences of individual coral species at our study locations can shed light on the environmental factors driving coral reef distribution in other locations of the ETP.

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Interactions of multiple abiotic stresses exacerbate mollusk diversity loss in a high-discharge coastal mangrove wetland

Published 9 October 2025 Science Closed
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Highlights

  • A long-term study of mangrove water and mollusk diversity in Chinses Daya Bay
  • Water temperature, chlorophyll-a, total nitrogen and phosphorus rise significantly
  • Water pH, salinity, dissolved oxygen and mollusk diversity reduce greatly
  • Long-term high emission cause multiple stressors and biodiversity loss
  • Interactions between multi-water factors exacerbate mollusk diversity loss

Abstract

Coastal regions, as a hotspot region of biodiversity and the most densely populated areas in the world, are increasingly threatened by anthropogenic disturbances, including warming, acidification, eutrophication, salinity fluctuation, and oxygen loss. Although massive single-factor studies have revealed the ecological catastrophe caused by these impacts, how these impact stressors interact to endanger coastal biodiversity that is critical for ecosystem stability and human well-being is still poorly understood. To investigate whether and how water warming, acidification, eutrophication, salinity fluctuation and oxygen loss interact with each other to impact the mangrove mollusk diversity, a long-term study was conducted in the mangroves of Chinese Daya Bay from 1987–1993 to 2017–2021. We found that water temperature, chlorophyll-a, total nitrogen (TN) and total phosphorus (TP) increased significantly, while the water pH, salinity, dissolved oxygen (DO) and mollusk species richness decreased obviously, reflecting water warming, eutrophication, acidification, salinity fluctuation, oxygen loss and biodiversity loss occurred in the Daya Bay. The mangrove mollusk diversity had a significant response to the water warming, eutrophication, acidification, salinity fluctuation, oxygen loss (p < 0.001). The average incidences of mollusk diversity loss due to the changes in water pH, temperature, TP, TN, chlorophyll-a, salinity and DO were 47.11 %, 35.56 %, 35.53 %, 34.48 %, 34.22 %, 34.15 % and 33.05 %, respectively. Moreover, the average effect of interactions between any two water factors on the mollusk diversity was 0.998, which was 22.5 % larger than their single effect on biodiversity of 0.814. The findings suggest that interactions between global change stressors can exacerbate biodiversity loss in coastal wetlands. Quantifying those effects in terms of multi-factor interactions will contribute to the coastal management and restoration based upon combined evidence rather than a one-sided single perspective.

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Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario

Published 7 October 2025 Science Closed
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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.

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Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression

Published 18 September 2025 Science Closed
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Highlights

  • OA stimulates the colonization of the pathogenic bacterium Mycoplasma.
  • Microbiota dysbiosis and oxidative damage trigger intestinal inflammation.
  • OA causes significant epithelial damage to the intestines of C. nobilis.
  • Physiological suppression of C. nobilis is decreased in a pH-dependent manner.

Abstract

Ocean acidification (OA) poses significant threats to marine calcifiers through multifaceted physiological disruptions. While bivalve mollusks are particularly vulnerable, the intestinal defense mechanisms against OA-induced stress remain poorly characterized. This study systematically investigated the intimate associations between the organismal physiological toxicity responses and intestinal homeostasis of Chlamys nobilis (C. nobilis) under simulated OA situations (pH 7.3–8.0) to reveal the potential physiological and biochemical damage. The results revealed that acidification stimulated pathogenic bacteria(Mycoplasma)colonization, disrupted microbiota homeostasis, and induced oxidative responses, thereby triggering intestinal inflammation and epithelial damage. Furthermore, the filtration rates and oxygen consumption rates of C. nobilis were significantly decreased in a pH-dependent manner across all the treatments, which might result from the intestinal dysfunction and the inhibition of acetylcholinesterase activities. These findings establish a link between OA-induced intestinal dysbiosis and organismal physiology, providing novel insights into the interplay between physiological performance and intestinal homeostasis under OA scenarios. The results advance our understanding of bivalve mollusk adaptation strategies and inform predictive models for its sustainability in acidifying marine ecosystems.

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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.

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

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’

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