The co-cultivation of seaweeds with bivalve shellfish is a potential strategy for protecting bivalve crops against anthropogenic coastal acidification and hypoxia. We co-cultivated seaweeds and bivalves using a succession of seaweed species according to season (winter, Saccharina latissima → spring, Ulva spp. → summer, Gracilaria spp.) together with eastern oysters (Crassostrea virginica) and blue mussels (Mytilus edulis). Bivalves and seaweeds were deployed in two estuaries that contrasted in trophic state, one mesotrophic and one eutrophic. In all five experiments in the mesotrophic system, cocultivation with seaweeds significantly increased weight- and/or shell-based growth of bivalves (p < 0.05). Growth rate increases for C. virginica were modest, with weight-based growth improving by 17–21% and shell-based growth improving by 3–27% with seaweed co-culture of all macroalgal species. For M. edulis, the effect was large; co-culture with S. latissima caused 47% and 114% increases in shell- and weight-based growth rates, respectively. In the four experiments in the eutrophic estuary, co-culture with seaweeds did not significantly improve bivalve growth. Seaweed cultivation significantly improved water quality metrics (increased pH and dissolved oxygen (DO); p < 0.05 in all cases) in and around the seaweed sites at both locations, although increases in pH and DO were modest, and even in control treatments, there were no prolonged periods of harmful pH or DO levels. An abundance of macroalgal detritus may have bolstered the diets of co-cultivated bivalves in the mesotrophic estuary, a hypothesis supported by lower chlorophyll a concentration, and therefore lower planktonic food levels, at that site. Given that seaweeds display species-specific allelopathic effects against phytoplankton, it is also possible that the presence of seaweeds altered the phytoplankton community to the benefit of the bivalves. Regardless, the findings here demonstrate that co-cultivation with seaweeds can accelerate the growth of bivalves.
Continue reading ‘Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries’Posts Tagged 'algae'
Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries
Published 29 December 2025 Science Leave a CommentTags: algae, biological response, BRcommunity, chemistry, field, fisheries, mitigation, mollusks, morphology, North Atlantic
Impact of acidification and ultraviolet radiation on the physiology of Ulva fasciata
Published 19 December 2025 Science ClosedTags: adaptation, algae, biological response, laboratory, light, Mediterranean, multiple factors, otherprocess, photosynthesis, physiology
Ocean acidification and increased UVR exposure driven by factors such as global warming, ozone layer depletion and anthropogenic activities are impacting the physiology and ecology of macroalgae in species-specific, diverse and complex ways. This study aims to investigate the individual and combined effects of ocean acidification and ultraviolet radiation (UVR) on the physiological responses of the cosmopolitan macroalgae species Ulva fasciata. The algae samples were cultured under laboratory conditions at two different pH levels (8.2 and 7.7) and under either the presence or absence of UVR. In U. fasciata, the maximum quantum efficiency of photosystem II (Fv/Fm) decreased with low pH and UVR, and a synergistic stress response was observed when these two stressors were applied together. The relative electron transport rate (rETRmax) varied depending on pH, while UVR increased this rate. These findings indicated that U. fasciata samples were under physiological stress. The incubation period significantly affected rETRmax and showed that the organism developed time-dependent adaptation responses. Alpha, a photosynthetic efficiency indicator, was negatively affected by UVR, whereas the light saturation point (Ik) varied as a result of the interaction between incubation time, pH, and UVR. The findings suggest that UVR exerted a more pronounced inhibitory effect on the photosynthetic system and growth of U. fasciata than low pH. Furthermore, combined exposure to UVR and low pH resulted in stronger growth inhibition, and a significant interaction between the two stressors was observed. Low pH and UVR exposure caused increased carbonic anhydrase activity (CA), while high CO2 led to a decrease in nitrate reductase activity (NR). UV-absorbing compounds (UVACs) were significantly affected by low pH and culture duration, whereas the effect of UVR on these compounds became significant only through its interaction with the incubation period. This suggests that the effect of UVR emerges through temporal accumulation. The findings reveal that this species is capable of developing late-phase acclimation strategies in response to environmental stress factors and possesses a potential adaptive capacity to cope with future marine change scenarios.
Continue reading ‘Impact of acidification and ultraviolet radiation on the physiology of Ulva fasciata’Exploring structural integrity of coralline algae in response to the environmental changes associated with the PETM: a tale of functional resistance
Published 11 December 2025 Science ClosedTags: algae, biological response, field, Indian, morphology, paleo
Coralline algae are key benthic components of shallow-marine ecosystems globally and as habitat-formers they support high biodiversity levels. Experiments on living coralline algae show internal growth changes in response to warming and higher CO2. These growth changes are leading to weakened structural integrity and increased breakage impacting their ecological function of habitat formation. Short-term experiments, though, raise questions about long term acclimation over multiple generations. Coralline algae have an extensive fossil record across the Cenozoic. Analysing growth changes within the geological record, specifically across hyperthermals, geologically abrupt environmental changes in the Earth’s history characterized by rapid ocean warming, acidification and sea level rise, can complement modern experiments. This allows us to quantify the vulnerability and response of habitat formers, such as coralline algae, to long-term environmental change. We evaluated cellular structure and structural integrity in species of the genera Sporolithon and Lithothamnion from Meghalaya, NE India (Eastern Tethys) before and during the Paleocene-Eocene Thermal Maximum, PETM (~55.8 Ma), the most pronounced hyperthermal of the Cenozoic. Cellular structural changes were not uniform between species, some species showed increased stress and strain due to larger cell sizes during the PETM, while other species revealed negligible changes in cell sizes. Unexpectedly, stresses and strains experienced by these Palaeogene taxa are comparable to contemporary species of the study genera. These findings suggest a resilience to long term warming and lower pH conditions resulting in a resistance to breakage. However, species differences in environmental change responses potentially highlight variations in phenotypic plasticity.
Continue reading ‘Exploring structural integrity of coralline algae in response to the environmental changes associated with the PETM: a tale of functional resistance’Asymmetric effects of acidification and warming on foundation species and their predators in the California rocky intertidal zone
Published 11 December 2025 Science ClosedTags: algae, BRcommunity, calcification, laboratory, mesocosms, mollusks, morphology, multiple factors, North Pacific, performance, photosynthesis, respiration, temperature
The effects of climate change on marine organisms act through multiple pathways, as ocean warming and acidification can affect both their physiology and interspecies interactions. Asymmetries in species-specific physiological responses to climate change may alter the strength of interactions, such as those between predator and prey, which will have cascading effects on ecosystem structure. How foundation species and their interactions are affected by climate change will profoundly affect their community due to their dominance. I assessed the physiological responses of two common California rocky intertidal consumer–resource pairs across multiple trophic levels. I measured metabolic rates after four weeks of exposure to a range of nine pH levels (7.2–8.0) at two temperature levels (ambient, +4°C). At the lowest trophic level, I examined the effects of climate change on a primary producer foundation species, Silvetia compressa (golden rockweed), and its herbivore, Tegula eiseni, under differing upwelling regimes in early and late spring. Rockweed responded more to acidification than warming, decreasing photosynthetic rates in early spring and increasing rates during late spring. Their snail consumer, however, responded most strongly to temperature—increasing both respiration rates and calcification under warm conditions in late spring. In addition to species specific responses to climate stressors, the rockweed–snail pair had context-dependent responses based on background environmental conditions. Greater upwelling during late spring, combined with a younger snail population could explain differences in responses between early and late spring. Next, I examined asymmetries between a calcifying foundation species, Mytilus californianus, and its whelk predator, Nucella emarginata. Specifically, mussels were generally resistant to acute exposure to ocean warming and acidification, while whelks were highly sensitive to temperature. Whelks decreased their calcification, respiration, shell extension, and probability of drilling a mussel under warmer conditions. Across both experiments, I observed asymmetries in response to changes in pH and temperature between consumer and resource, which can shift ecosystems between bottom-up and top-down processes. Overall, I showed that mesopredators, such as herbivorous and carnivorous snails, appeared to be the most sensitive to changes in temperature relative to their foundation species prey. Climate change may reshape rocky intertidal communities by altering predation patterns on foundation species, which could either facilitate or threaten the survival of other associated species in a changing environment.
Continue reading ‘Asymmetric effects of acidification and warming on foundation species and their predators in the California rocky intertidal zone’Progressive changes in coral reef communities with increasing ocean acidification
Published 8 December 2025 Science ClosedTags: algae, BRcommunity, chemistry, community composition, corals, field, otherprocess, vents
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.
Continue reading ‘Progressive changes in coral reef communities with increasing ocean acidification’Warming coupled with elevated pCO2 modulates microplastic inhibition in a commercial red alga Pyropia haitanensis
Published 5 December 2025 Science ClosedTags: algae, biological response, growth, laboratory, multiple factors, North Pacific, photosynthesis, physiology, plastics, temperature
Highlights
- Microplastics exert concentration-dependent negative effects on Pyropia haitanensis.
- Warming (24 °C) exacerbated microplastic-induced growth inhibition at ambient CO₂ level.
- High CO₂ inhibited growth at 20 °C but enhanced it at 24 °C under high microplastic stress.
Abstract
Ocean acidification, warming, and microplastics are pervasive stressors in coastal ocean, yet their combined effects on economically important seaweed Pyropia haitanensis remain unclear. To investigate how elevated pCO2, warming, and microplastics interact to affect physiology of P. haitanensis, we cultured thalli at ambient (418 μatm, AC) and elevated (1000 μatm, HC) CO2 levels with two temperatures (20 and 24 °C), and a gradient of microplastics (0.025, 2.5, 25, 50, 100 mg L−1) in a controlled indoor experiment. Our results indicate that microplastics imposed a strong, concentration-dependent stress on P. haitanensis, consistently reducing relative growth rate (RGR), Fv/Fm, photosynthetic pigments (chlorophyll a, carotenoids, and phycobiliproteins), and cellular reserves (soluble protein and carbohydrates), with the strongest inhibition observed at concentration of 100 mg L−1. However, while the increased temperature (24 °C) promoted the content of pigments and soluble protein of the thalli, it decreased the content of soluble carbohydrate among the microplastic concentrations regardless of pCO2 levels. It is noteworthy that under ambient pCO2 level, elevated temperature exacerbated the growth inhibition caused by microplastics, resulting in the highest inhibition rate of 57 % occurring at 100 mg L−1. In contrast, this temperature-aggravated microplastic toxicity was mitigated by high pCO2 levels, with the inhibition rate of 32 % at the highest microplastic concentration. These findings reveal that while elevated pCO2 and warming can modulate microplastic stress via physiological reallocation, persistent declines in photochemical efficiency and light-harvesting pigments may constrain yield and nutritional quality of P. haitanensis where microplastics are high in coastal aquaculture area.
Continue reading ‘Warming coupled with elevated pCO2 modulates microplastic inhibition in a commercial red alga Pyropia haitanensis’Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value
Published 1 December 2025 Science ClosedTags: algae, Antarctic, biological response, chemistry, field, physiology, vents
Highlights
- Chlorophyll a content in some seaweed species increased with latitude along the Antarctic Peninsula.
- Seaweeds from fumarole vent sites revealed variations in fatty acids and pigments.
- Lower nutritional value in Antarctic seaweeds from fumarole sites suggests potential responses to ocean warming and acidification.
- Species-specific biochemical shifts in Antarctic seaweeds are anticipated under global change scenarios.
Abstract
Global change is driving ocean warming (OW) and acidification (OA), impacting marine ecosystems worldwide, including polar regions. Seaweeds, as key primary producers in coastal ecosystems, synthesize a wide range of biochemical compounds that support higher trophic levels. Their biochemical composition is conditioned by local environmental factors, including seawater temperature, pH, and nutrient availability. However, how polar seaweeds respond to ongoing global change remains poorly understood. In this study, we examined the influence of local environmental changes on the biochemical composition – including fatty acids (FA), pigments, carbon, and nitrogen – of nine Antarctic brown and red seaweed species. Specifically, we considered a latitudinal gradient from the South Shetland Islands (⁓62°S) to Yalour Island (⁓65°S), and the presence of active fumarole vents at Deception Island. Our results reveal species-specific and location-dependent biochemical shifts in most species. While chlorophyll a concentrations tended to increase with latitude, specimens collected from fumarole vents exhibited a reduction in total FA content, PUFA:SFA (polyunsaturated to saturated fatty acid) ratios, PUFA omega-3, and pigment concentrations. These shifts under hydrothermal influence are likely driven by elevated seawater temperatures and acidic conditions, suggesting a potential decline in nutritional value under future global change scenarios. Additionally, higher magnesium content was found in the skeletons of crustose coralline algae from shallow waters than in those at 22 m depth. Our results highlight the species-specific nature of biochemical responses to environmental stressors, underlining the complexity of predicting the impacts of global change on seaweed physiology and the potential cascading effects on Antarctic food webs.
Continue reading ‘Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value’Sargassum’s health under ocean acidification and nitrogen boost
Published 25 November 2025 Press releases ClosedTags: algae
Ocean acidification and nutrient loading present significant threats to marine ecosystems, particularly to critical species like Sargassum hemiphyllum var. chinense. A groundbreaking study led by Chen et al., published in BMC Genomics, investigates how these stressors affect the physiological and transcriptomic responses of this seaweed. Researchers are gaining new insights into how climate change and nutrient enrichment may disrupt marine life, offering a glimpse into the resilience of Sargassum hemiphyllum and highlighting its ecological importance.
The study reveals intricate details about the adaptability of Sargassum hemiphyllum var. chinense in response to increasing temperatures and acidification levels. As global temperatures rise and CO2 emissions lead to ocean acidification, understanding how marine organisms react to these conditions becomes crucial. The researchers conducted a series of experiments simulating these stressors, measuring physiological changes in the algae over time. The findings suggest that while Sargassum hemiphyllum endures these challenges, the responses are profound and affect growth and survival.
Moreover, the meticulous transcriptomic analysis conducted by the researchers provides a robust framework for interpreting the complex changes triggered by environmental stressors. The team utilized RNA sequencing technology to evaluate gene expression profiles, revealing key pathways that the algae activate in response to both acidification and nitrogen enrichment. This revelation underscores the adaptability of marine flora and suggests potential avenues for increasing resilience against climate changes.
The physiological changes noted in Sargassum hemiphyllum are equally fascinating. The team observed variations in biomass, muscle integrity, and reproduction rates, providing concrete evidence that environmental conditions directly influence the survival and proliferation of this species. The implications are staggering, considering Sargassum hemiphyllum‘s role as a critical habitat for various marine organisms. The study calls attention to the interconnectivity within marine ecosystems and the potential cascading effects that might distress entire food webs.
Continue reading ‘Sargassum’s health under ocean acidification and nitrogen boost’Physiological and transcriptomic responses of Sargassum hemiphyllum var. chinense to ocean acidification and nitrogen enrichment
Published 21 November 2025 Science ClosedTags: algae, biological response, laboratory, molecular biology, multiple factors, North Pacific, nutrients, physiology
Sargassum hemiphyllum var. chinense is a major brown macroalga and has important ecological and economic significance. Ocean acidification and nitrogen enrichment are serious threats to marine ecosystems primarily by altering the physiology of organisms. However, the response of S. hemiphyllum var. chinense to the combined effects of ocean acidification and elevated nitrogen levels remains unclear. This study conducted a 7-day dual-factor experiment to investigate the physiological and transcriptional responses of S. hemiphyllum var. chinense under two CO2 levels (400 μatm and 1000 μatm) and two NO3⁻ levels (50 μmol/L and 300 μmol/L). The results showed that high CO2 and NO3− concentrations promoted the synthesis of photosynthetic pigments including qN and NPQ. Physiological results showed that high CO2 and the combined high NO3− and CO2 treatments enhanced growth rate and NO3− uptake rate, but NR activity was significantly decreased. Transcriptome analysis identified differentially expressed genes involved in oxidative phosphorylation, carbon metabolism, the TCA cycle, and nitrogen metabolic pathways. Notably, genes related to oxidative phosphorylation and TCA cycle were significantly up-regulated under high NO3− and dual-factor treatments, suggesting that carbohydrate metabolism and energy metabolism of S. hemiphyllum var. chinense were significantly enhanced. The qRT-PCR analysis revealed that the expression levels of key genes involved in carbon fixation and nitrogen metabolism, including PFK, PRK, GAPDH, Rubisco, NR, and MDH, were significantly downregulated. These findings elucidate the molecular mechanisms by which S. hemiphyllum var. chinense adapts to ocean acidification and nitrogen enrichment, offering valuable insights for understanding its capacity to withstand changing marine environments.
Continue reading ‘Physiological and transcriptomic responses of Sargassum hemiphyllum var. chinense to ocean acidification and nitrogen enrichment’Impact of seawater acidification on the growth, nutritional composition, sensory profile, and antioxidant activity of Caulerpa racemosa in laboratory culture
Published 20 November 2025 Science ClosedTags: algae, biological response, growth, laboratory, morphology, physiology, South Pacific
Fluctuations in coastal water pH, driven by ocean acidification, can strongly influence photosynthetic marine species, including seaweeds. This study investigated the effects of seawater acidification on the growth, nutritional composition, sensory profile, and antioxidant activity of the green alga Caulerpa racemosa. Cultured under varying pH levels (8.25, 8.00, 7.75, and 7.50) adjusted using HCl, C. racemosa exhibited significant morphological and biochemical changes. Lower pH conditions caused bleaching and textural brittleness, with pH levels between 7.50 and 7.75 showing the most pronounced impacts. Conversely, pH 8.25 supported optimal growth, with superior morphometric performance (absolute growth of 138.30 ± 3.70 g; specific growth rate of 3.08 ± 0.04% day⁻1). Acidification decreased chlorophyll content but enhanced carotenoids, indicating reduced photosynthetic efficiency. Protein content declined under acidic conditions, while lipid and carbohydrate levels increased. Notably, antioxidant activity peaked under pH 7.50 (15.09 ± 0.04%; IC50 275.04 ± 0.85 ppm), suggesting an adaptive physiological response. Sensory evaluation revealed that C. racemosa cultured at pH 8.25 achieved the highest overall acceptability, supporting its potential for culinary and nutritional use. These findings highlight the capacity of C. racemosa to acclimate to acidified environments, providing insights into its adaptive mechanisms and applications in food, pharmaceuticals, and sustainable aquaculture.
Continue reading ‘Impact of seawater acidification on the growth, nutritional composition, sensory profile, and antioxidant activity of Caulerpa racemosa in laboratory culture’Impact of crustose coralline algae, ocean acidification, and ocean warming on larval pinto abalone settlement and juvenile survival
Published 11 November 2025 Science ClosedTags: algae, biological response, BRcommunity, communityMF, laboratory, mollusks, morphology, mortality, multiple factors, North Pacific, reproduction, temperature
Highlights
- Ocean acidification reduced pinto abalone settlement and survival in the hatchery.
- Ocean acidification is likely a greater threat than warming to Washington pinto abalone.
- Use of a natural settlement inducer improves abalone settlement and survival.
- Coralline algae may improve survival of pinto abalone under ocean acidification.
Abstract
Since 1994, Washington State (USA) has experienced a 97 % drop in the native pinto abalone population. Since 2007, conservation aquaculture initiatives have been underway to return the population to a self-sustaining level. Successful restoration, however, depends on both the ability to successfully raise juveniles in hatchery settings and the capacity of outplanted pinto abalone to survive and reproduce in the wild as threats of ocean acidification and warming continue to increase. Crustose coralline algae (CCA) can play an important role in restoration efforts by acting as natural inducers of larval settlement. Additionally, studies have shown that CCA can create a boundary layer with elevated pH, potentially providing a refuge for benthic species. We examined the settlement of pinto abalone under different environmental conditions (7.90 pH/14 °C (ambient), 7.90 pH/18 °C, 7.55 pH/14 °C; and 7.55 pH/18 °C) using two substrates: CCA-covered rocks and clean rocks with GABA (a chemical settlement inducer). Low pH negatively impacted larval settlement. Though settlement was higher with CCA than with GABA, this difference was not statistically significant. Juvenile survival was negatively impacted by low pH, but positively impacted by CCA presence, demonstrating the potential of CCA to increase juvenile pinto abalone survival and ameliorate the negative effects of low pH. Using CCA in hatchery culture and selecting sites with CCA cover for pinto abalone outplants may improve the efficiency of restoration in Washington.
Continue reading ‘Impact of crustose coralline algae, ocean acidification, and ocean warming on larval pinto abalone settlement and juvenile survival’Biogeochemical properties of shallow-water CO2 seeps on Himeshima Island and Showa Iwojima Island, Japan
Published 7 November 2025 Science ClosedTags: algae, biological response, BRcommunity, chemistry, community composition, field, North Pacific, otherprocess, vents
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.
Continue reading ‘Biogeochemical properties of shallow-water CO2 seeps on Himeshima Island and Showa Iwojima Island, Japan’Elevated carbon dioxide does not increase macroalgal community photosynthesis
Published 4 November 2025 Science ClosedTags: algae, biological response, community composition, field, North Pacific, otherprocess, photosynthesis, vents
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.
Continue reading ‘Elevated carbon dioxide does not increase macroalgal community photosynthesis’The negative responses and acclimation mechanisms of Neopyropia yezoensis conchocelis filaments to short- and long-term ocean acidification
Published 30 October 2025 Science ClosedTags: adaptation, algae, biological response, growth, laboratory, molecular biology, North Pacific, otherprocess, photosynthesis, physiology
Background
Ocean acidification (OA) significantly alters the carbonate chemistry of seawater, leading to a decrease of seawater pH to impact the physiological and biochemical processes of those intertidal macroalgae. Previous studies have focused on the response of macroalgae to OA at thallus stage, while the effects at filamentous stage remain insufficiently explored.
Results
This study investigated the physiological-biochemical and molecular mechanisms of the filamentous conchocelis stage (the diploid sporophyte) of Neopyropia yezoensis responding to short- (5 days) and long-term (20 days) OA (2000 ppm CO2, pH 7.53). The results showed that short-term OA rapidly inhibited the growth and photosynthesis, suppressed chlorophyll synthesis and nitrogen assimilation, and down-regulated genes associated with photosynthesis, Calvin cycle, and carbohydrate metabolism of N. yezoensis conchocelis filaments. However, N. yezoensis conchocelis filaments showed acclimation strategies under long-term OA, in terms of metabolic reorganization, prioritizing stress tolerance over growth. Further weighted gene co-expression network analysis (WGCNA) based on the metabolomic and transcriptomic results under long-term OA showed that the strategy was manifested by the accumulation of soluble sugars as osmolytes, lipid β-oxidation compensating for energy deficits, and H+ extrusion mediated via ABC transporters.
Conclusions
This study suggested time-depended responses of N. yezoensis conchocelis filaments to OA, proving the pronounced negative effects of OA on N. yezoensis conchocelis filaments, revealing N. yezoensis conchocelis filaments could acclimate to long-term OA by resource reallocation. These findings provide new insight into the survival of N. yezoensis conchocelis filaments under OA, and facilitate the development of technologies and breeding strategies for improved acidification tolerance in N. yezoensis.
Continue reading ‘The negative responses and acclimation mechanisms of Neopyropia yezoensis conchocelis filaments to short- and long-term ocean acidification’Dulse seaweed Devaleraea mollis mitigates effects of ocean acidification on larval Pacific oysters Magallana gigas
Published 21 October 2025 Science ClosedTags: algae, biological response, BRcommunity, chemistry, laboratory, mitigation, molecular biology, mollusks, morphology, North Pacific, reproduction
Ocean acidification (OA), driven by upwelling and climate change, can negatively impact the ecological and economic contribution of marine calcifiers along coasts worldwide. OA interferes with calcification, particularly in early life stages, causing mortality, reduced growth, and morphological abnormalities in shellfish such as the Pacific oyster (Magallana gigas). This issue is gaining traction as climate change intensifies, placing shellfish in wild populations and farms alike at risk. Macroalgal photosynthesis by seaweed such as Pacific dulse (Devaleraea mollis) has been proposed to provide small-scale OA refuges, but few controlled experiments quantify this effect, and none have focused on larval shellfish. This study examines the potential for Pacific dulse to mitigate OA and its effects on Pacific oyster larvae. Under continuous light for 23 days, the presence of dulse resulted in a consistent increase in seawater aragonite saturation state by 0.1-0.9, and pH by 0.1-0.5 units, depending on OA condition. Newly fertilized oysters were reared for 48 hours in the absence or presence of dulse under treatments corresponding to ambient (pH 7.8, 450 μatm CO₂), future OA (pH 7.6, 800 μatm CO₂), and future OA + upwelling (pH 7.4, 1200 μatm CO₂) seawater conditions. Dulse fully mitigated OA effects on larval size that ranged from decreases of 5% to 10%. Under the future OA + upwelling treatment, dulse presence reduced the odds of underdeveloped oyster larvae at 14 hours post fertilization (hpf), and larvae with hinge abnormalities at 24 hpf, by over 50%. Dulse induced minor changes to immune response gene expression at 48 hpf. These findings highlight the benefits of seaweed when adjacent to organisms sensitive to OA. These findings will be particularly useful for shellfish farms, habitat restoration efforts, and ocean stewardship practices as a potential mitigation strategy under the changing climate.
Continue reading ‘Dulse seaweed Devaleraea mollis mitigates effects of ocean acidification on larval Pacific oysters Magallana gigas’Macroalgae farming increases DO and pH, reduces pCO2 and nutrients, and enhances blue carbon potential
Published 17 October 2025 Science ClosedTags: algae, biogeochemistry, biological response, chemistry, field, fisheries, mitigation, North Pacific
Edible macroalgal cultivation is increasingly promoted as a nature-based solution to mitigate coastal eutrophication and improve seawater quality. However, the species-specific impacts and spatial extent of these ecological effects remain poorly understood, particularly in semi-enclosed bays with complex hydrodynamics. This study aims to quantify the biogeochemical influence of two widely cultivated species—Porphyra haitanensis and Hizikia fusiformis—on seawater carbonate chemistry and nutrient levels in Yueqing Bay, eastern China. High-resolution field surveys were conducted at 52 stations, enabling direct comparisons between cultivated and non-cultivated waters. Geostatistical modeling, including spherical semivariograms and Empirical Bayesian Kriging, was applied to delineate species-specific influence zones and quantify changes in key water quality parameters. P. haitanensis farming induced broad, kilometer-scale improvements in seawater chemistry, including elevated dissolved oxygen (DO) (+ 2.72%) and pH (+ 0.09 units), and significantly lower partial pressure of CO2 (pCO2) (− 118 µatm), relative to distant reference sites (all p < 0.05). A slight increase in total phosphorus (TP) (+ 0.007 mg L− 1) was also observed, likely reflecting nearby riverine inputs. In contrast, H. fusiformis cultivation produced more localized (< 100 m) but significant changes, including reductions in dissolved inorganic carbon (DIC) (− 1.84 mg L− 1) and pCO2 (− 82.6 µatm), alongside increases in DO (+ 1.72%), pH (+ 0.02 units), and chlorophyll-a (Chl-a) (+ 0.72 µg L− 1) (all p < 0.05). These results provide the first fine-scale, species-resolved spatial assessment of macroalgal farming effects on water quality in a semi-enclosed bay. By quantifying distance-dependent ecological responses, this study offers science-based guidance for spatial planning, nutrient management, and blue carbon integration—particularly as the routine harvest of biomass facilitates net carbon export from coastal waters. These findings highlight the potential of macroalgal farming as a scalable, multifunctional nature-based solution for sustainable aquaculture and climate mitigation.
Continue reading ‘Macroalgae farming increases DO and pH, reduces pCO2 and nutrients, and enhances blue carbon potential’Global meta-analysis reveals the impacts of ocean warming and acidification on kelps
Published 9 October 2025 Science ClosedTags: algae, biological response, multiple factors, physiology, reproduction, review, temperature
Kelp forests are among the most diverse and productive ecosystems in the world, providing critical habitat for numerous ecologically and economically important species. However, kelps are at risk from climate change, and declining populations worldwide demonstrate the need to characterize and quantify the effects of anthropogenic stressors on kelp physiology. Here, we performed a meta-analysis on true kelps (order Laminariales) in response to ocean warming and acidification based on a global synthesis of 7000 data points from 143 experimental studies. Our results show that ocean warming has a strong negative impact on kelps at all life stages and across various physiological levels, including growth, reproduction, and survival. In contrast, ocean acidification generally has no effect, except for its negative impact on reproduction. In most cases, co-occurring warming and acidification acted synergistically. Response to warming, acidification, and multiple driver scenarios increased as the intensity and duration of exposure increased. In our analyses, the genera Eualaria, Hedophyllum, Lessonia, and Postelsia were among the most vulnerable to warming. Studies conducted in the temperate northern Pacific showed extreme negative effects of warming. We also identify key gaps in our understanding of kelp responses to climate change, such as the impacts on microscopic spores and the combined effects of warming and acidification. This analysis synthesizes trends in a rapidly expanding field of literature and provides a deeper understanding of how kelps will respond to a rapidly changing ocean.
Continue reading ‘Global meta-analysis reveals the impacts of ocean warming and acidification on kelps’Editorial: impacts of climate change on seaweeds
Published 6 October 2025 Science ClosedTags: algae, biological response, review
Climate change is drastically altering the composition and abundance of seaweed-dominated ecosystems throughout our oceans. Ocean warming and associated intensifying marine heatwaves (Wernberg et al., 2016; Bunting et al., Trautmann et al., Gendall et al., Khen et al.), ocean acidification (Koch et al., 2013; Comeau and Cornwall, 2016), and deoxygenation (Altieri et al., 2021) can all impact the physiology of seaweeds and the ecological roles that they play. Ocean warming can cause long-term shifts in the ranges of seaweed species, usually in the form of range retractions at warm edges and expansions at cool edges (Straub et al., 2016). Marine heatwaves can elicit acute heat stress in seaweeds, drive subsequent mortality, and result in phase shifts from one ecosystem type to another (Wernberg et al., 2016, 2024). Ocean acidification causes the slow transformation of ecosystems from those dominated by coralline algal substrate to those characterised by a variety of turfing seaweeds or microalgae (Cornwall et al., 2024). Increasing intensity of ocean deoxygenation and frequency of acute localized events will likely exacerbate the effects of localized threats, but the effects of deoxygenation on seaweed communities remain poorly understood compared to other climate change-linked stressors (Altieri et al., 2021). Additionally, increased sedimentation caused by land use changes and increased storm frequencies brought on by climate change (termed ‘coastal darkening’), is also an important stressor of seaweed communities (Blain et al., 2021). Increased sedimentation can interact with other stressors (e.g., temperature) or act on its own to alter the composition and function of seaweed-dominated ecosystems (Wernberg et al., 2024). To better predict and project how seaweed-dominated ecosystems will fare in the future, we require extensive further evidence regarding how the effects of climate change will manifest on seaweeds of all types across temperate, tropical, and polar regions.
Continue reading ‘Editorial: impacts of climate change on seaweeds’The effects of ocean acidification on the epiphytic bacterial community of Sargassum thunbergii via high-throughput sequencing
Published 11 September 2025 Science ClosedTags: abundance, adaptation, algae, biological response, BRcommunity, community composition, laboratory, molecular biology, nitrogen fixation, North Pacific, otherprocess, physiology, prokaryotes
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’Influence of intensified upwelling on two different Corallina officinalis Linneo 1758 populations by exploring direct and indirect effects
Published 26 August 2025 Science ClosedTags: adaptation, algae, biological response, laboratory, otherprocess, photosynthesis, physiology, South Pacific
In the perspective of a future ocean, climate change can alter upwelling systems globally. Along the Chilean coast, upwelling becomes intensified, leading to cool temperatures and low pH, which can affect common and widespread calcifying seaweed species such as Corallina officinalis. We measured physiological, biomineralogical, and palatability responses in two distinct populations originating from contrasting upwelling regimes, one from an upwelling area and the other from an upwelling shadow, by exposing them to current and future upwelling conditions. After 20 days of experimentation, photosynthetic responses such as maximum quantum yield (Fv/Fm) remained high (> 0.5) across populations. In contrast, maximal photosynthetic efficiency (rETRmax), light saturation point (Ek) and pigment content were higher in individuals exposed to future conditions, while alpha (electron transport efficiency) decreased over time. The carbonate content was higher in individuals exposed to future conditions, while the organic matter content differed between populations, with lower contents in the population originating from the site with higher environmental variability (-1.1%). Individuals exposed to future upwelling conditions presented higher soluble protein contents (2-3 mg/g wet weight) and were also more consumed by sea urchins (+162.7%). Our results indicate that the two C. officinalis populations possess strategies that confer tolerance to projected increases in upwelling, demonstrating their capacity to adapt to changing environmental conditions. However, rising herbivory pressure associated with intensified upwelling may exert a stronger influence on ecosystem dynamics, potentially altering future community composition.
Continue reading ‘Influence of intensified upwelling on two different Corallina officinalis Linneo 1758 populations by exploring direct and indirect effects’
