Body size is a fundamental characteristic of all living organisms that determines physiological functions and life-history traits. Ecological theory predicts that ocean acidification can cause body size reductions, confirmed by several studies reporting miniaturization in ectotherms. Based on this prediction, we would expect a broad suite of species to show similar plastic body-size responses to elevated CO2. Using four natural climate change analogues of ocean acidification across the northern and southern hemispheres, we quantified body size alterations across 18 marine invertebrate and fish taxa to test for climate-driven miniaturization. Only three species consistently showed body-size reductions under ocean acidification: one urchin and two fish species. In contrast, 15 other species, ranging from highly calcified to non-calcified, displayed unchanged or increased body sizes or inconsistent miniaturization. If body-size miniaturization responses were consistently reproducible across taxa we would have observed it more frequently, suggesting that species responses to ocean acidification are more variable than previously thought and likely vary depending on a species’ physiology and life history. Thus, rather than entire communities undergoing miniaturization, species are likely to display a spectrum of responses, with some exhibiting size reductions, others demonstrating physiological resistance to elevated CO2, and others potentially benefiting from the indirect effects of ocean acidification.
Continue reading ‘Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification’Posts Tagged 'otherprocess'
Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification
Published 18 June 2026 Science Leave a CommentTags: algae, annelids, biological response, BRcommunity, bryozoa, cnidaria, community composition, corals, crustaceans, echinoderms, fish, Indian, laboratory, mollusks, morphology, North Pacific, otherprocess, physiology, vents
Shifts of tentacles-associated prokaryotes of Anemonia viridis along a natural pH gradient
Published 18 June 2026 Science Leave a CommentTags: biological response, BRcommunity, cnidaria, community composition, laboratory, Mediterranean, molecular biology, otherprocess, physiology, prokaryotes, sediment
Highlights
- A. viridis tentacle microbiomes were studied under changing natural pH conditions.
- Notable shifts in the abundance of specific taxa emerged in the acidified sites.
- Differences in seawater emphasized the host’s unique microbial signature.
- Rickettsiales predominance suggested a specialized ecological role in symbiosis.
- Further research is needed to discern the role of microbes for host resilience.
Abstract
Marine hydrothermal vents are extreme environments that naturally select for organisms with strong resistance and the ability to cope with special conditions of acidification. Sea anemones are an interesting example that are able to buffer intracellular pH conditions. In this study, the influence of a natural pH gradient on microbial communities associated with Anemonia viridis (Cnidaria, Anthozoa) tentacles was investigated. We hypothesized that exposure to a natural pH gradient would be associated with changes in the structure and activity of A. viridis-associated microbial communities, potentially contributing to the host’s resilience in hydrothermal environments. Microbial enzymatic activities within anemones’ tentacles were investigated by incubation with fluorogenic compounds. The leucine amino peptidase activity was highest in the tentacles of specimens living in more acidified sites. A microbial biodiversity loss was observed in bacterial symbionts from less acidified to more acidified sites, with a reduction of relative abundance in certain groups (i.e., Planctomycetota, Firmicutes, and Desulfobacterota). Results obtained by a metabarcoding approach provided interesting insights into the taxonomic shifts of the A. viridis holobiont system in naturally acidified environments.
Continue reading ‘Shifts of tentacles-associated prokaryotes of Anemonia viridis along a natural pH gradient’Response of HAB-forming microalgae competition to ocean acidification, warming, and changing light fields
Published 17 June 2026 Science Leave a CommentTags: algae, biological response, BRcommunity, community composition, growth, laboratory, light, multiple factors, otherprocess, phytoplankton, temperature
In recent years, the East China Sea (ECS) has experienced frequent harmful algal blooms (HABs), driven by the complex interplay of climate change—specifically ocean warming and acidification—and eutrophication-induced light attenuation. Despite their ecological significance, the interactive effects of these environmental stressors on the competitive dynamics between bloom-forming microalgae remain poorly understood. This study aimed to elucidate how warming, reduced light, and elevated CO2 influence the competition between two dominant diatoms. We conducted controlled monoculture and mixed-culture experiments using two key species: Skeletonema costatum and Chaetoceros curvisetus. The experimental design incorporated varying levels of CO2, temperature, and light intensity to simulate future coastal scenarios. Growth rates, peak cell densities, and successional patterns were monitored to assess competitive outcomes under multiple stressors. Monoculture results indicated that high temperature and low light intensity promoted the growth of both species. However, in mixed cultures, these conditions significantly accelerated the time to reach peak density and induced a definitive successional shift from S. costatum to C. curvisetus. Notably, while the general successional pattern was consistent, elevated CO2 further enhanced the competitive advantage of C. curvisetus, particularly when combined with high-temperature and low-light scenarios. These findings suggest that the synergy of future warming, declining light availability, and intensified ocean acidification in the ECS will likely favor C. curvisetus over S. costatum. This shift may increase the frequency of HAB events dominated by C. curvisetus, driving significant climate-related restructuring of phytoplankton communities in coastal ecosystems.
Continue reading ‘Response of HAB-forming microalgae competition to ocean acidification, warming, and changing light fields’Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island
Published 16 June 2026 Science Leave a CommentTags: biogeochemistry, biological response, chemistry, cnidaria, community composition, corals, field, Indian, otherprocess, vents
Gas hydrates modulate methane and carbon dioxide benthic fluxes into the ocean and usually occur embedded in the sediment. Here we use acoustic surveys alongside optical and geochemical observations from remotely operated vehicles to show that CO2 hydrate mounds are forming directly on the seafloor atop a large liquid CO2 vent field offshore Mayotte Island. The venting, which initiated following volcanic activity in 2018, deleteriously impacts surrounding coral communities due to local acidification.
Continue reading ‘Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island’Coastal phytoplankton response to acidification and warming under differing levels of nutrient availability
Published 12 June 2026 Science Leave a CommentTags: biological response, community composition, mesocosms, multiple factors, nutrients, otherprocess, photosynthesis, phytoplankton, South Pacific
Ocean acidification and warming will alter phytoplankton biomass and composition, yet despite numerous studies, there are few consistent responses on which to base predictions. To determine the responses of chlorophyll-a and phytoplankton size and composition to predicted lower pH (−0.33 to −0.5) alone, and also combined with elevated temperature (+2.5–3.5 °C), two mesocosm experiments were carried out in austral spring and autumn in temperate New Zealand coastal waters. Lower pH alone had no effect on chlorophyll-a in either experiment and, as the treatment pH was lower than the pH minimum recorded in a parallel four-year time series, this lack of response in chlorophyll-a was not attributable to prior in situ exposure. Conversely, chlorophyll-a increased under lower pH and warming in both experiments, with the large (>20 µm) phytoplankton size fraction showing opposing responses under nutrient deplete and replete conditions. Diatom biomass also increased in both treatments when nutrient availability was maintained, with a dominant pennate species Cylindrotheca clostridium emerging. The results highlight the value of contextual time series for experimental interpretation, and also the importance of assessing warming and acidification together using regionally representative nutrient concentrations, for prediction of coastal phytoplankton response to climate change.
Continue reading ‘Coastal phytoplankton response to acidification and warming under differing levels of nutrient availability’Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica
Published 3 June 2026 Science ClosedTags: algae, biological response, community composition, corals, echinoderms, field, modeling, North Pacific, otherprocess, photosynthesis, physiology, regionalmodeling
Reef-building corals form the calcium-carbonate frameworks that underpin tropical coral reefs, yet global coral cover has declined by ~50% in recent decades, due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that buffer stress, promote recovery, and enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photo-physiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and richer in chlorophyll a. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin cover, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp.. When significant, photophysiological measurements showed 9.7 – 44.5% higher photosynthetic efficiency (Fv’/Fm’) in Papagayo corals and 19.94 – 42.75 % higher maximum photosynthetic rates (Pmax) in Sámara corals. These results highlight how contrasting environmental regimes within a relatively small geographic area can shape distinct coral community compositions and photophysiological strategies, with implications for identifying areas of reef persistence or refugia.
Continue reading ‘Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica’Hydrodynamic control of coral metabolism: a coupled modeling approach linking flow, physiology, and reef-scale biogeochemistry
Published 2 June 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, corals, individualmodeling, modeling, otherprocess, physiology, South Pacific
Tropical coral reefs exhibit high variability in coral metabolism, driven by complex interactions among physical, chemical, and biological processes. Understanding the spatiotemporal patterns of coral metabolism and their drivers is critical, as such variability may underpin corals’ adaptive capacity to withstand a warming and acidifying ocean. Here, we use a coupled hydrodynamic–biogeochemical–physiological model to investigate spatial and diel variations in coral metabolic processes (photosynthesis, respiration, and calcification) across Moorea’s north shore reef system under three prevailing wave regimes. We find that photosynthesis varies little across the reef, whereas respiration and calcification show pronounced spatial heterogeneity. These spatial patterns closely mirror the ones in seawater carbonate chemistry and depend strongly on wave-driven flow. Hydrodynamics regulate diffusive exchanges between coral tissues and surrounding seawater, and eventually generate distinct internal chemical environments (in the coelenteron and calcifying fluid) across the reef. Landward reef regions exhibit the greatest spatial and diel variability in coral metabolism. Low-wave, slow-flow conditions amplify metabolic fluctuations throughout the reef, but more strongly in the landward regions. Overall, our results highlight how interactions among transport processes, carbonate chemistry, and coral physiology produce strong day-night fluctuations and spatially heterogeneous but structured metabolic patterns across the reef, which vary systematically with wave conditions.
Continue reading ‘Hydrodynamic control of coral metabolism: a coupled modeling approach linking flow, physiology, and reef-scale biogeochemistry’Feeding and excreting ecology in coastal systems
Published 26 May 2026 Science ClosedTags: biological response, community composition, growth, laboratory, mollusks, morphology, mortality, otherprocess, performance, physiology
Oysters (Crassostrea virginica) are critical foundation species in estuaries, providing numerous ecological and economic benefits. However, oyster populations have diminished worldwide. Effective oyster restoration and aquaculture require a mechanistic understanding of the physiological and environmental factors that govern oyster feeding, growth, and resilience under changing coastal conditions. We investigated how oyster ploidy and environmental conditions influenced oyster feeding and investigated how changes in abiotic conditions affected behavioral performance of oyster drills (Stramonita spp.), a key oyster predator. To better understand feeding responses and behaviors of both predator and prey we 1) used in-situ filter feeding assays to determine feeding differences existed amongst diploid and triploid oysters, 2) gathered a baseline for growth and in-situ feeding rates of oysters across Mississippi Sound in the Northern Gulf in the Spring, Summer, and Fall, 3) simulated present-day and projected future pH conditions (7.0-8.8) to analyze oyster feeding responses, and 4) introduced oyster drills to acidified conditions (7.0-8.8) to monitor behavior and foraging rates. Diploid oysters exhibited higher overall feeding rates, yet equivalent absorption efficiency between ploidies demonstrates a difference in energy allocation which might be the key to triploids’ ability to grow quickly. These findings highlight the role of intrinsic genetic and physiological traits in shaping oyster performance and provide a baseline for interpreting responses to environmental variability. Across spatial and seasonal variation in oyster in-situ feeding and growth across three contrasting sites in Mobile Bay and Mississippi Sound, in the Northern Gulf on the western border of Alabama and Mississippi, results revealed strong spatial and seasonal variability in feeding and growth. This was driven primarily by seston composition and salinity. Under present-day and projected future ocean acidification conditions, overall oyster feeding rates declined with lower pH’s, absorption efficiency remained stable, suggesting partial physiological compensation. These results indicate that pH can impose sublethal constraints on energy acquisition and growth, with individual variability at extreme pH highlighting potential acclimation or tolerance thresholds. When subjecting the oyster’s predator, the oyster drill, to similar pH conditions (7.0-8.8) experimental results indicate that decreased pH may increase drill foraging times. Behaviors like inactivity and climbing out of the water indicate a stress response under both high and low pH, demonstrating the complexity of predicting predator-prey outcomes under more acidic conditions. Collectively, these chapters demonstrate that oyster feeding, growth, and survival are shaped by both intrinsic traits, such as ploidy, and extrinsic factors including environmental variability and ocean acidification. Understanding the interplay between physiological plasticity, seston quality, and predator-prey interactions is essential for informing restoration and aquaculture strategies that sustain ecological function and the ecosystem services oysters provide.
Continue reading ‘Feeding and excreting ecology in coastal systems’Microbial communities associated with two populations of the sponge Chondrilla nucula under present and projected climate conditions in the Aegean Sea
Published 25 May 2026 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, Mediterranean, molecular biology, otherprocess, porifera, prokaryotes
This data paper describes bacterial and fungal communities associated with the sponge Chondrilla nucula collected from two Eastern Mediterranean populations (North and South Aegean Sea) and maintained under controlled common-garden conditions simulating present and projected climate scenarios over a period of 3 months. Microbial composition was characterised using two complementary ribosomal marker approaches: Illumina (MiSeq) sequencing of the 16S rRNA gene for Bacteria and Oxford Nanopore (MinION) sequencing of a long 18S-ITS-28S rRNA fragment for Fungi. A total of 24 sponge libraries (3 climate conditions x 2 populations x 4 biological replicates) along with six control libraries (water from three experimental tanks, extraction and PCR blanks) were constructed for each group of microsymbionts. The resulting reads were processed using custom and publicly available bioinformatic pipelines and databases, followed by initial taxonomic assignment. This dataset represents the first fungal community associated with C. nucula and the first bacterial community for this species from the Aegean Sea.
Continue reading ‘Microbial communities associated with two populations of the sponge Chondrilla nucula under present and projected climate conditions in the Aegean Sea’Carbon allocation strategy of Thalassiosira weissflogii in response to elevated pCO2
Published 25 May 2026 Science ClosedTags: adaptation, biological response, laboratory, molecular biology, otherprocess, photosynthesis, physiology, phytoplankton
Diatoms are of significance in the marine ecosystem, playing a pivotal role in the sustenance of marine life and the transfer of carbon from the surface ocean to deeper waters. Although numerous studies have investigated the effects of elevated carbon dioxide (CO2) on marine diatoms across both short- and long-term adaptation scales, the molecular mechanisms governing chitin metabolism in response to ocean acidification remain poorly understood. In this study, we employed an integrated approach combining transcriptomic, metabolomic, and physiological analyses to examine the marine diatom Thalassiosira weissflogii following 40-day acclimation to high-CO2 conditions. Physiological studies have demonstrated that ocean acidification has the capacity to result in an augmentation of the C/N ratio, chitin content, maximum PSII quantum yield (Fv/Fm), and photosynthetic pigment content of T. weissflogii. Analysis of chlorophyll fluorescence dynamics further demonstrated enhanced primary photochemical efficiency of PSII in the acidified treatment group. Consistent with this, the transcriptome results also showed that the photosynthesis-related pathways were upregulated to meet the increased material and energy requirements after adaptation to elevated CO2 levels. More importantly, it was determined that acidification treatment resulted in the upregulation of chitin synthesis and the downregulation of chitin degradation in T. weissflogii, consequently leading to an augmentation in chitin content. These findings indicate that ocean acidification (high CO2, low pH) prompts T. weissflogii to prioritize the allocation of carbon resources to the synthesis of chitin. The synthesis of chitin may reinforce cell wall formation as an adaptive response to ocean acidification. Our research provides new insights into the marine acidification adaptation strategies of T. weissflogii.
Continue reading ‘Carbon allocation strategy of Thalassiosira weissflogii in response to elevated pCO2’High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning
Published 14 May 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, corals, field, laboratory, North Pacific, otherprocess, phanerogams, physiology, reproduction
Highlights
- Seagrass-coral habitats act as CO2 sources driven by intense nighttime respiration
- High-resolution data enable predictive modeling of DIC, DOC, and POC dynamics
- Metabolic cues govern DIC, while temperature and alkalinity regulate POC and DOC
- Episodic coral spawning and rainfall trigger rapid ocean acidification
- Short-term disturbances dramatically shift organic and inorganic nutrient loads
Abstract
Seagrass meadows and coral reefs are global hotspots for productivity, yet they are often studied in isolation despite their intense biogeochemical connectivity. Significant gaps remain in understanding how coupled inorganic and organic processes within the water column drive blue carbon services in such mixed habitats, particularly during rapid environmental disturbances. Here, we investigated a unique, intertwined ecosystem in the Dongsha Atoll, where massive Porites corals are distributed on seagrass meadows, creating a natural laboratory for studying water column carbon biogeochemistry. During a 10-day sampling period, we collected continuous hydrological and discrete biogeochemical data at two- to four-hour intervals. Our results reveal that the dissolved inorganic carbon (DIC) covaried with dissolved oxygen and pH in strong diurnal patterns, which were governed by photosynthesis and respiration. As an outcome, variable but mostly high pCO2 values (141–2070 μatm) indicate the seagrass meadow was a source of CO2 to the atmosphere due to strong night-time respiration. Particulate organic carbon (POC) increased with temperature but showed no diurnal pattern. Dissolved organic carbon (DOC) showed a weak diurnal pattern and was linked to variations in POC and total alkalinity, highlighting the tight coupling between the organic production of the meadow and the inorganic chemistry of the calcification framework. Additionally, coral spawning led to a surge in organic content and changed inorganic nutrient levels. Rainfall events significantly acidified the ocean and enhanced submarine groundwater discharge to the seagrass-coral habitat. The distinctive contributions of this study are the extremely high temporal resolution of discrete samples, allowing the simultaneous tracking of multiple organic and inorganic pools during natural disturbances. The high-resolution data provide fundamental information for parametrizing models that explain DIC, POC, and DOC, which yield insights into organic carbon cycling in seagrass meadow-coral habitats.
Continue reading ‘High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning’Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae
Published 29 April 2026 Science ClosedTags: algae, biological response, community composition, laboratory, mollusks, mortality, North Atlantic, otherprocess, reproduction
While harmful algal blooms (HABs) and ocean acidification (OA) are environmental factors that can impair bivalves, the manner in which these two stressors may act and interact to impact bivalve larvae is poorly understood. This study exposed larvae of hard clams (Mercenaria mercenaria) and Eastern oysters (Crassostrea virginica) to a range of pCO2 levels found in estuaries (400–3,000 µatm) and three harmful algae, Alexandrium catenella, Dinophysis acuminata, and Margalefidinium polykrikoides, at densities found during HABs (500–7,000 cells mL-1), with one HAB species exposure per experiment. The combined OA and HAB treatment significantly reduced larval survival in all 21 experiments by 91 ± 4.6% (SE) compared to controls and reduced larval sizes in 92% of experiments by 40 ± 3.5%. Cultured M. polykrikoides had a stronger negative effect on larvae than cellular equivalent bloom populations. Densities of D. acuminata >750 cells mL-1 reduced larval survival and size (p < 0.01), but the addition of OA to D. acuminata did not suppress survival further. While the combined A. catenella and OA treatment reduced larval growth and survival at all densities (p < 0.01), A. catenella alone did not impact M. mercenaria survival or size at or below 1,000 cells mL-1 and did not impact C. virginica at any density. Oyster larvae were less impacted than hard clams by OA (33 vs. 67% of experiments) and by HABs (67 vs. 100% of experiments). Given the very low survival of bivalve larvae when exposed to combined HABs and OA in all experiments (<0.1–5%), bivalve restoration and conservation efforts should seek to avoid regions that experience these co-stressors.
Continue reading ‘Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae’Nonlinear responses of phytoplankton size, diversity, and chlorophyll a to environmental forcing along the Yellow Sea
Published 20 April 2026 Science ClosedTags: biological response, community composition, field, morphology, North Pacific, otherprocess, physiology, phytoplankton
Highlights
- Miniaturization coincides with reduced species diversity and elevated chlorophyll a.
- Declining pH and reduced dissolved inorganic nitrogen are key drivers for smaller cells.
- Salinity, dissolved oxygen and cooling jointly reshape phytoplankton community structure.
Abstract
Phytoplankton are tiny drifting photosynthetic organisms that support marine food webs and help control the global carbon cycle. However, it remains unclear how ongoing environmental changes are altering their cell size, species diversity, and chlorophyll a concentration in coastal seas. In this study, we investigated changes in phytoplankton cell size, species diversity, and chlorophyll a concentration along the Yellow Sea coast of China from 2021 to 2024, based on fourteen research cruises conducted at twenty-six coastal stations. We then employed statistical models to explore how individual and combined environmental factors were related to those biological features. We observed a clear shift to predominance of smaller cells, a reduction in species diversity, and an increase in chlorophyll a concentration. pH and reduced dissolved inorganic nitrogen were strongly associated with smaller cell size, while higher salinity and higher oxygen were associated with lower diversity. Lower surface water temperature and higher dissolved oxygen were associated with higher chlorophyll a concentrations. Overall, our findings suggest that interacting changes in pH, nutrient supply, temperature, salinity, and oxygen are associated with a simpler phytoplankton community structure, smaller mean cell size, and higher biomass levels in the Yellow Sea coastal region, with potential consequences for local food webs and carbon cycling.
Continue reading ‘Nonlinear responses of phytoplankton size, diversity, and chlorophyll a to environmental forcing along the Yellow Sea’Effects of pH on phytoplankton growth and diversity in a tropical coastal ay: an experimental study
Published 14 April 2026 Science ClosedTags: biological response, BRcommunity, community composition, growth, Indian, laboratory, otherprocess, phytoplankton
This research was intended to investigate the effects of reduced pH on the growth rates and diversity of phytoplankton in the coastal waters of Visakhapatnam in the Bay of Bengal. A short-term (six days) microcosm experiment was conducted with different pH conditions such as ambient (control-in situ pH), pH 8.0 (0.2 pH units drop from in situ pH) and pH 7.8 (0.4 pH units drop from in situ pH) corresponding to low, medium, and high future pH decline scenarios, respectively, to study the direct acidification impact on phytoplankton. The results revealed that the phytoplankton communities exhibit a wide range of responses including changes in growth rate during incubation. From the two treatments, a more pronounced response was observed in pH 7.8 conditions compared to the present pH scenario. Some phytoplankton communities exhibited positive growth responses to acidification, while others showed negative reactions in terms of biodiversity. Notably, Pseudo-nitzschia sp. became dominant during acidification, whereas larger centric diatoms such as Skeletonema spp., Chaetoceros spp., Rhizosolenia sp., Dactyliosolen fragilissimus, and Ditylum brightwellii showed no significant growth response to upcoming acidified conditions. This indicates a diverse array of physiological tolerance among the plankton species to environmental shifts. This study recommends further research to explore the impact of ocean acidification on other planktonic species in the coastal waters of Bay of Bengal.
Continue reading ‘Effects of pH on phytoplankton growth and diversity in a tropical coastal ay: an experimental study’Unravelling marine benthic functioning shifts under ocean acidification
Published 10 April 2026 Science ClosedTags: algae, biological response, BRcommunity, calcification, community composition, crustaceans, field, Mediterranean, mollusks, morphology, otherprocess, photosynthesis, physiology, porifera, respiration, vents
Ocean acidification (OA) driven by increasing atmospheric CO2 is altering marine biodiversity. However, impacts of OA on ecosystem functioning at the community level, including calcification, primary production and nutrient uptake, remain largely unknown. Here, we conducted community transplant experiments at natural CO2 vents to assess how declining pH affects marine community species composition, biomass, and key ecosystem processes over time. Our results indicate that community shifts caused by declining pH lead to decreased biomass and calcification rates, while photosynthesis and nutrient uptake rates increased. By leveraging OA field model systems and in situ measurements of ecosystem functioning, this study provides critical insights into how OA-induced biodiversity loss reshapes the structure and functioning of temperate marine coastal ecosystems.
Continue reading ‘Unravelling marine benthic functioning shifts under ocean acidification’Climate-driven restructuring of phytoplankton productivity and community composition in the south-eastern Black Sea: insights from seasonal CO2-temperature manipulation experiments
Published 9 April 2026 Science ClosedTags: biological response, Black Sea, community composition, laboratory, multiple factors, otherprocess, physiology, phytoplankton, temperature
Semi-enclosed marine systems with low buffering capacity, such as the Black Sea, are expected to experience amplified impacts of ocean acidification and warming, yet experimental evidence on their combined short-term effects on natural phytoplankton assemblages remains limited. Here, we present a seasonally resolved one-year study (four experiments conducted between 2022 and 2023) based on 48 h short-term microcosm incubation experiments using natural phytoplankton communities collected from coastal and offshore stations in the south-eastern Black Sea. CO2 concentrations (360, 600, and 760 ppm) and temperature (ambient and +3 °C) were manipulated to examine short-term physiological and compositional responses under projected climate scenarios. We hypothesised that CO2 and warming would exert both independent and interactive effects on short-term particulate organic carbon production (14C uptake rates) and relative community composition, with responses varying seasonally and being most pronounced during summer stratification.
Short-term particulate primary production increased by ∼22% and ∼36% at 600 and 760 ppm CO2, respectively (p<0.05), while warming provided an additional 14–22% enhancement depending on season, with significant CO2 × temperature interaction terms detected for total production (two-way ANOVA, p<0.05), indicating synergistic CO2–temperature effects. Warming and moderate CO2 enrichment were associated with increased relative contributions of nano- and picophytoplankton (by ∼6–10%), whereas high CO2 reduced the warming-driven shift toward smaller cells by maintaining microphytoplankton contributions ∼10–15% higher than in the warming-only treatment. Carbonate chemistry responded strongly to CO2 manipulation, with pH declining from in-situ values of 8.09–8.21 to 7.06–7.52 during incubations and minor reductions in total alkalinity, reflecting the weak buffering capacity of the system. Pigment composition and microscopy indicated short-term increases in dinoflagellate relative abundance (∼12–18%) and concurrent declines in diatom markers, accompanied by accelerated nitrate depletion and reduced nitrogen-to-phosphorus (N:P) ratios, consistent with enhanced nitrogen limitation.
Overall, these findings demonstrate pronounced short-term sensitivity of natural phytoplankton assemblages in the south-eastern Black Sea to combined CO2 and warming under controlled incubation conditions. Because these results derive from 48 h microcosm experiments, they represent short-term physiological and compositional responses rather than direct evidence of long-term ecosystem restructuring, yet the observed patterns suggest potential implications for trophic efficiency, harmful algal bloom development, and carbon cycling in this low-buffer, stratified basin under future climate forcing.
Continue reading ‘Climate-driven restructuring of phytoplankton productivity and community composition in the south-eastern Black Sea: insights from seasonal CO2-temperature manipulation experiments’Responses of reef fish populations to similar environmental changes across distant oceanic islands
Published 9 April 2026 Science ClosedTags: abundance, adaptation, biological response, chemistry, field, fish, otherprocess, South Atlantic
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.
Continue reading ‘Responses of reef fish populations to similar environmental changes across distant oceanic islands’Investigation of the adaptive mechanisms to ocean acidification in Patella species from CO2 vent systems of the Mediterranean Sea
Published 7 April 2026 Science ClosedTags: adaptation, biological response, field, Mediterranean, molecular biology, mollusks, morphology, otherprocess, physiology, respiration, vents
The continuous increase in anthropogenic carbon dioxide (CO2) emissions into the atmosphere is one of the main factors contributing to ocean acidification (OA). In fact, CO2 is partially absorbed by the oceans, where it alters carbonate chemistry and seawater pH, which is expected to decrease from the current level of 8.1 to 7.7 by 2100. OA exerts harmful impacts primarily on calcifying organisms, as it affects the availability of carbonates, which makes their calcareous structures thinner and more fragile. Moreover, several studies have described the detrimental effects of OA across many marine taxa, affecting important physiological and metabolic mechanisms. On the other hand, research conducted at CO2 vent systems, which are volcanic naturally acidified sites, showed that several organisms can survive under acidified conditions through specific tolerance and/or adaptive strategies. Among these organisms, the gastropod Patella spp. is one of the few calcifiers capable of inhabiting naturally acidified sites, such as the Castello Aragonese vent systems at Ischia Island and the San Giorgio vent systems at Sicily Island. Nonetheless, the complex mechanisms that allow survival and potential adaptation of these organisms to natural OA conditions need to be understood. Therefore, this PhD study aimed at investigating the potential molecular, physiological, metabolic, genetic, and epigenetic mechanisms that enable these organisms to tolerate and survive under OA conditions through a stepwise approach. Specifically, this PhD research attempted to answer the following questions: • Does OA entail a stressful condition in resident populations of Patella spp. living at reduced pH conditions, thereby affecting their overall well-being and health status? • Are there specific physiological, metabolic, and biochemical mechanisms that contribute in defining tolerance to OA? • Are limpets genetically adapted to OA? • Is DNA methylation contributing to promote tolerance to OA in limpets? • What is the role of environmental conditions in shaping the response to OA? The first chapter of this thesis considered three Patella species (P. caerulea, P. rustica, and P. ulyssiponensis) collected from the CO2 vent systems of the Castello Aragonese (Ischia Island). This vent system exhibits a natural acidification gradient ranging from ambient pH (N1: pH = 8.1), to intermediate pH (N2: pH = 7.7), and to extremely low pH (N3: pH < 7.4). Resident populations were collected along the gradient and at San Pietro, an additional ambient pH site (pH = 8.1), located at a distance of 4 km from the Castello vent. In addition, a 30-day in situ transplant experiment was conducted using P. caerulea, in order to evaluate the short-term responses induced by OA. Morphometric traits, such as shell length, height, width, and soft-tissue weight, were measured, and a set of biomarkers related to antioxidant system, energy metabolism, neurotoxicity, and biomineralization was applied. For resident populations, P. caerulea showed increased size and energy reserves at the extremely acidified site, likely related to a shift from erect calcified algae to biofilm, or to reduced competition and/or predatory pressure under acidified conditions. Biochemical endpoints measured in both P. caerulea and P. ulyssiponensis were not modified by OA. Conversely, P. rustica exhibited significant modulation of nearly all biochemical parameters, likely due to its different position on the rocky shore, which makes this species more exposed to tidal fluctuations and therefore to an additional source of disturbance, besides OA. Short-term exposure of P. caerulea to OA resulted in a decrease in protein content and an increase in glycogen content at the extremely acidified site, with the induction of superoxide dismutase and glutathione-S-transferase activities at intermediate pH, suggesting the activation of compensatory mechanisms to cope with reduced pH conditions. Overall, results revealed a distinct response to OA of the three species of Patella. Moreover, the increased size and energy-related endpoints observed in P. caerulea and P. rustica highlighted the need to further investigate energy metabolism aspects, in order to better understand the trade-offs between compensatory mechanisms and the energetic cost underlying tolerance to OA. Based on these evidences, the second chapter focused exclusively on P. caerulea, with the aim of deeply investigating metabolic and physiological stress-responses, comparing resident populations of the Castello Aragonese vent systems and transplanted organisms, similarly to the first chapter. Respiration and ammonia excretion rates were measured four times across the year. Additionally, untargeted metabolomics analyses were performed to investigate metabolic pathways potentially involved in response to OA. Only during summer, OA increased respiration rate in limpets from the most acidified site, while simultaneously reduced excretion rates, likely to allocate more energy resources to face the increasing temperature, besides OA. Furthermore, both resident and transplanted populations up-regulated carnitine metabolism, suggesting that OA induced an increase of energy production through β-oxidation and subsequent Krebs cycles. Moreover, several metabolites involved in osmoregulation, oxidative stress, and nucleic acid mechanisms were increased. Overall, results seem to confirm the presence of negative effects and of an energetic cost underpinning tolerance to OA. The third and final chapter investigated the potential influence of phenotypic plasticity, genetic adaptation, and DNA methylation in tolerance to OA in adult and juvenile populations of P. caerulea collected from two CO2 vent systems of the Mediterranean Sea. Adult and juvenile specimens were sampled along the acidification gradient of the Castello Aragonese vent systems of Ischia Island (San Pietro/N1: pH = 8.1; N2: pH = 7.7; N3: pH < 7.4) and from the San Giorgio vent systems of Sicily Island (Patti: pH = 8.1; San Giorgio: pH = 7.8). Following genomic DNA extractions from foot tissue and individual libraries preparation with the NEB Next® Enzymatic Methyl-seq Kit, samples were sequenced on the Illumina NovaSeq 6000 sequencer. Data processing and analyses were conducted on Euler platform mainly using biscuit tool, which enabled to simultaneously extract genomic and epigenomic information from DNA methylation sequencing. Population genomics and epigenomics analyses revealed divergent patterns between the Ischia and Sicily populations. Populations from the Ischia vent revealed marked signs of genomic differentiation, particularly in adults from the intermediate and extremely low pH sites, while reduced differences in DNA methylation levels were detected, especially in adults. These findings suggest a strong signature of purifying selection acting on standing genetic variation, through a within-generation response, likely driven by the more pronounced pH fluctuations occurring at these sites. Conversely, no genomic differentiation was observed between the Sicily populations, but greater differences in DNA methylation were detected between acidified and non-acidified sites at both adult and juvenile stages. These results revealed that this epigenetic mechanism, rather than genomic changes, may play a key role in the response to the milder pH variations of this vent and potentially enhance organisms’ tolerance to OA. In conclusion, this PhD project investigated tolerance to OA in limpets through a holistic approach that, for the first time, integrated morphological, physiological, metabolic, biochemical, genetic, and epigenetic analyses. Overall, findings revealed that Patella spp. has the ability to survive under acidified conditions even though with a physiological and metabolic cost, which could be partially compensated by more favorable environmental conditions. This study further highlights the importance of conducting research in naturally acidified environments, since it allows to formulate more realistic hypotheses about the ability of marine organisms to persist in future changing oceans.
Continue reading ‘Investigation of the adaptive mechanisms to ocean acidification in Patella species from CO2 vent systems of the Mediterranean Sea’Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish
Published 2 April 2026 Science ClosedTags: adaptation, biological response, fish, laboratory, morphology, mortality, North Atlantic, otherprocess, reproduction
Ocean acidification (OA) is a major climate-related threat to fish that can disrupt the regulation of the reproductive axis of fish, impacting reproductive success. However, previous studies have only focused on a single reproductive cycle and reported increased fecundity in some species exposed to OA. Since acclimation over several reproductive cycles can occur, it is necessary to evaluate successive reproductive cycles for predicting the actual resilience of species to OA. In this study we assessed the impact of lifetime exposure to different ocean pH/pCO2 levels (Current condition, Moderate OA and High OA) on the sexual maturation and spawning phenology of the European sea bass, over its two first reproductive periods. We tested the hypothesis that OA would exert its greatest impact at the onset of puberty (first reproduction). Accordingly, High OA exposure induced an earlier onset of puberty in both sexes, resulting in a longer spawning period and an increased fecundity. These effects were reduced during the second reproductive season. However, OA affected egg quality and sperm motility profile during the second reproductive season, leading to a total mortality at hatching of embryos spontaneously produced. This mortality was not observed in embryos produced through hormone-induced oocyte maturation and in vitro fertilisation. These results suggest that OA affects the regulation of oocyte maturation and/or the synchronisation of eggs and sperm release. The OA-driven shift in spawning may misalign with optimal environmental conditions for offspring survival. This increases the population’s vulnerability and could favour species whose reproduction is more resilient to OA.
Continue reading ‘Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish’Impacts of ocean acidification on marine zooplankton: a review of physiological, developmental, and reproductive responses
Published 31 March 2026 Science ClosedTags: adaptation, biological response, otherprocess, physiology, reproduction, review, zooplankton
Acidification. The increasing levels of carbon dioxide CO₂ in the atmosphere are leading to ocean acidification, and this is altering the chemical content of marine water and is endangering life in the oceans. The examples of marine zooplankton, including Copepods, Pteropods, krill, and larvae of invertebrates are essential to the pelagic food webs and carbon cycles, even though they differ in their tolerance to low PH concentration and high pCO₂ levels. Early developmental phases are particularly vulnerable, with them showing retardation in developmental stages, reduced hatch rates, physical deformities as well as a lack of calcification. Higher carbon dioxide CO₂ levels interfere with the acid-base balance, increase oxidative stress and alter the allocation of metabolism, leading to trade-offs that lower growth, reproduction and survival rates. Calcifying organisms such as the pteropods are highly susceptible whereas some of the non-calcifying copepods exhibit a level of physiological resilience. Negative effects of other stressors may be affected by increased temperature, oxygen depletion, and nutrient enrichment which may further compound negative effects. There is some evidence that there is some possible acclimation in the short term and that there might be transgenerational plasticity but we do not understand adaptive capacity in the long term. Knowledge gaps exist in regard to multigenerational response, non-calcifying and gelatinous species and how physiological plasticity occurs. Species-specific responses are an important aspect of predictive models to estimate the impact of the ecosystem and guide conservation efforts. To ensure marine ecosystems remain stable as ocean acidification continues, vulnerable zooplankton should be safeguarded to preserve tropic structure, nutrient cycling, and nutrient stability.
Continue reading ‘Impacts of ocean acidification on marine zooplankton: a review of physiological, developmental, and reproductive responses’
