Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.
Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’Posts Tagged 'community composition'
Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean
Published 17 August 2026 Science Leave a CommentTags: biological response, community composition, Indian, laboratory, otherprocess, photosynthesis, physiology, phytoplankton
Warming and acidification shape zooplankton community dynamics in Jiaozhou Bay: evidence from an Acid-Heat Vector Intensity Index
Published 10 August 2026 Science Leave a CommentTags: biological response, community composition, field, laboratory, North Pacific, otherprocess, zooplankton
Highlights
- Warming and coastal acidification shape Jiaozhou Bay zooplankton dynamics.
- AHIvec summarizes monitoring-oriented surface temperature-pH departure.
- GAMs showed nonlinear, zone-specific zooplankton response patterns.
Abstract
Ocean warming and coastal acidification often co-occur in nearshore embayments, yet their joint associations with zooplankton remain difficult to characterize because responses are frequently nonlinear and spatially heterogeneous. In this study, we developed an integrated quantitative framework for characterizing joint warming-acidification exposure in Jiaozhou Bay. Based on six cruises conducted at nine stations in May (spring) and August (summer) from 2022 to 2024, we characterized zooplankton communities using abundance, biomass, Shannon-Wiener diversity (H′), and Pielou’s evenness (J). We further introduced a joint-exposure indicator, the Acid-Heat Vector Intensity Index (AHIvec), which summarizes joint temperature-pH departure based on standardized anomalies of temperature and pH. Generalized additive models (GAMs) were then applied to examine nonlinear response patterns and zone-specific associations between environmental gradients and zooplankton community attributes. Within the 2022–2024 observation window, sea surface temperature was generally higher in 2024 than in 2022, whereas surface pH was generally lower; however, these patterns should be interpreted as short-term observations rather than formal long-term trend estimates. Zooplankton also showed pronounced spring-summer and spatial variability. Notably, abundance showed pronounced temporal variation and generally increased with temperature, whereas biomass peaked at intermediate temperatures (∼20–22 °C) and declined thereafter, indicating a mismatch between abundance and biomass. Although pH-related associations were weaker than temperature-related associations, they became more evident at the lower end of the observed pH range (approximately 7.7–7.9). The AHIvec gradient was associated with contrasting zone-specific patterns in zooplankton community attributes. Overall, recent temperature-pH variations were associated with changes in zooplankton abundance, biomass, and diversity in Jiaozhou Bay. The AHIvec + GAM framework provides a monitoring-oriented complement to direct temperature-pH analyses for characterizing joint exposure in coastal ecosystems.
Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea
Published 4 August 2026 Science ClosedTags: biological response, community composition, field, laboratory, mesocosms, North Pacific, otherprocess, physiology, phytoplankton, primary production, respiration
Anthropogenic CO2 emissions and their continuous dissolution into seawater lead to seawater pCO2 rise and ocean acidification (OA). Phytoplankton groups are known to be differentially affected by carbonate chemistry changes associated with OA in different regions of contrasting physical and chemical features. To explore responses of phytoplankton to OA in the Chinese coastal waters, we conducted a mesocosm experiment in a eutrophic bay of the southern East China Sea under ambient (410 µatm, AC) and elevated (1000 µatm, HC) pCO2 levels. The HC condition stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness in both pCO2 treatments were reduced during this stage due to the rapid nutrient consumption and diatom blooms, and the subsequent shift from diatoms to hetero-dinoflagellates led to a decline in primary production during the mid and later phases under nutrient depletion. HC treatment suppressed the diatom-to-dinoflagellate succession and enhanced the subsequent remineralization of organic matter, thereby facilitating smaller phytoplankton to dominant and sustaining primary production. Our findings indicate that, the impacts of OA on phytoplankton diversity in the coastal water of the southern East China Sea depend on availability of nutrients, with primary productivity and biodiversity of phytoplankton reduced in the eutrophicated coastal water.
Continue reading ‘Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea’Interplay between nutrient limitation and ocean acidification: plankton community shifts in the oligotrophic western Bay of Bengal
Published 30 July 2026 Science ClosedTags: biological response, community composition, Indian, morphology, multiple factors, nutrients, otherprocess, phytoplankton
Highlights
- Nutrient limits the phytoplankton growth in the Bay of Bengal due to stratification.
- Picoplankton dominated the phytoplankton community in the Bay.
- An increase in phytoplankton biomass was observed in response to ocean acidification (OA) in nutrient-rich regions.
- Decrease in phytoplankton biomass, bacteria and microzooplankton abundance was found in the nutrient-poor regions.
- Nutrient limitation overshadow the ocean acidification impact in the Bay of Bengal.
Abstract
The perennial rise in atmospheric carbon dioxide (CO2) from anthropogenic activities increased oceanic carbon uptake, thereby lowering seawater pH. Rapid ocean acidification (OA) by 2 to 3 times than other regions of the same latitudinal belts was reported in the Bay of Bengal (BoB) due to the deposition of atmospheric pollutants, in addition to the dissolution of atmospheric CO2. Therefore, the impact of OA on phytoplankton composition is hypothesized to be greater in the BoB than elsewhere in the globe. On the other hand, the BoB experiences intense oligotrophic conditions due to strong stratification driven by nutrient-poor freshwater discharge from major rivers, which is the primary bottleneck for phytoplankton growth, rather than carbon. It is hypothesized that nutrient limitation may overshadow OA’s impact on plankton in the BoB. To test this hypothesis, six microcosm experiments were conducted in the western BoB between 13 and 20°N with different nutrient levels in the surface waters. The pH of the surface water was adjusted by 0.2 units below the ambient pH using CO2 gas bubbling to simulate the projected OA scenario for the year 2100. Following pH adjustment, incubations were carried out for three days. Picoplankton dominated the phytoplankton community (∼96%) at all stations, with prochlorophytes as the dominant group. Among the phytoplankton, procholorophytes, diatoms, and prymeniophytes increased due to OA across all stations, while other groups of phytoplankton were declined. The increase in phytoplankton biomass was observed in the nutrient-rich stations, while a decrease in phytoplankton biomass, bacteria and microzooplankton abundance was found in the nutrient-poor stations, suggesting that nutrient availability dominated over the OA. Under a business-as-usual scenario, an increase in stratification due to melting Himalayan glaciers is projected, leading to strong stratification and reduced nutrient inputs through vertical mixing in the future in the BoB. Under such a scenario, nutrient limitation may possibly overshadow the OA impact in the future, despite a rapid decline in pH driven by increased CO2 dissolution and deposition of atmospheric pollutants.
Continue reading ‘Interplay between nutrient limitation and ocean acidification: plankton community shifts in the oligotrophic western Bay of Bengal’Experimental evidence of climate change effects on plankton community respiration in European coastal waters: current insights and knowledge gaps in tested disturbances and studied areas
Published 29 July 2026 Science ClosedTags: biological response, community composition, otherprocess, phytoplankton, respiration, review
Plankton community respiration (PCR) plays a central role in aquatic ecosystems, driving the breakdown of organic matter and influencing global carbon cycling through its contribution to the production and consumption of carbon and oxygen. Coastal areas are regarded as metabolic hotspots in the oceans, due to their intense biological and biogeochemical activities. This review synthesizes experimental evidence to explore how environmental constraints and climate drivers affect PCR in European coastal waters. In total, 46 studies were found in which PCR was measured during experiments testing the effects of one or multiple global climate change drivers in European coastal waters. Among them, the majority of experiments focused on changes in temperature, nutrient concentrations and stoichiometry, and/or pH, while other stressors were less studied. In addition to this qualitative synthesis, a quantitative meta-analysis was conducted on warming and acidification experiments, the only drivers for which comparable experimental designs were available. This analysis, based on 19 warming and 6 acidification studies, was used to perform a standardized comparison of effect sizes across studied areas and experimental set-ups. This review highlights critical knowledge gaps, notably regarding non- and understudied areas and understudied interactions between stressors that occurs jointly in ecosystems.
Continue reading ‘Experimental evidence of climate change effects on plankton community respiration in European coastal waters: current insights and knowledge gaps in tested disturbances and studied areas’Response of Zostera japonica rhizosphere bacteria to ocean acidification
Published 24 July 2026 Science ClosedTags: biological response, community composition, laboratory, molecular biology, North Pacific, otherprocess, phanerogams, photosynthesis, prokaryotes
Abstract
Amidst global climate change, the escalating atmospheric CO2 levels have intensified ocean acidification (OA), significantly impacting the structure and function of marine ecosystems. Seagrass beds, representative nearshore ecosystems, play a pivotal role in carbon sequestration, biodiversity preservation, and nearshore environmental equilibrium. Rhizosphere microorganisms within seagrass beds, essential components of the ecosystem, drive material cycling and energy flow. Their community structure and functions demonstrate heightened sensitivity to environmental variations. While previous studies have primarily focused on the effects of ocean acidification on seagrass hosts, limited attention has been given to the rhizosphere. Therefore, this study selected Zostera japonica as the focal species and systematically evaluated changes in the structure and function of the rhizosphere bacterial community across varying acidification levels (400 ppm, 1,000 ppm, 2,000 ppm CO2) within an ocean acidification context. The results revealed a significant decline in the richness and diversity of the rhizosphere bacterial community under acidification, accompanied by shifts in community composition characterized by an increase in the relative abundance of Bacteroidota and Tenacibaculum with escalating acidification levels. In high acidification conditions, bacterial network interactions exhibited a trend toward simplification; yet the number of key taxonomic units increases, and there was a shift in community assembly from stochastic to deterministic processes. Functional predictions indicated the enhancement of microbial carbon sequestration and nitrogen fixation under acidification, while denitrification and specific sulfur metabolism pathways were inhibited. This implies that in acidified environments, the rhizosphere bacterial community may enhance carbon and nitrogen fixation to uphold nutrient supply.
Importance
Against the background of escalating global climate change and ocean acidification, seagrass beds, as crucial blue carbon sink ecosystems, face formidable challenges to their ecological functions and stability. Rhizosphere microorganisms of seagrasses, serving as the “second genome” of the seagrass host, play a central role in material cycling, nutrient supply, and system stability within seagrass beds. They are a key biological component that supports seagrass adaptation to environmental changes. Therefore, investigating the response and adaptation mechanisms of seagrass rhizosphere bacterial communities under ocean acidification is essential for deepening our understanding of the stability and resilience of seagrass bed ecosystems.
Continue reading ‘Response of Zostera japonica rhizosphere bacteria to ocean acidification’Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait
Published 23 July 2026 Science ClosedTags: Arctic, biological response, community composition, field, laboratory, modeling, multiple factors, otherprocess, oxygen, photosynthesis, primary production, prokaryotes, regionalmodeling, respiration
Highlights
- Remote sensing indicates declining bloom in cold and developing bloom in warm water
- Primary production peaks in polar and arctic surface water masses
- Bacterial production is coupled to primary production despite thermal sensitivity
- Oxygen-based community respiration is highest in warmer water masses
- Oxygen-based and INT-based respiration estimates differ by an order of magnitude
Abstract
The Fram Strait is the primary oceanic gateway to the Arctic Ocean and has highly dynamic oceanographic conditions. Oceanographic conditions can shape community compositions, which is increasingly shown using molecular studies, but rate measurements remain scarce, especially for respiration in the Arctic Ocean. Here, we assessed primary production (PP), bacterial production (BP), bacterial abundances (BA), and community respiration (CR) using Winkler titrations and in vivo Iodo-Nitro-Tetrazolium (INT) reduction within the upper 50 m across water masses of the Fram Strait that had varying bloom conditions in spring 2021. We complemented in situ observations with remote sensing of sea surface temperature (SST) and chlorophyll-a (SSC) to infer bloom phenology in warm (θ>2°C), intermediate (2>θ>0°C), and cold (θ<0°C) waters using remote sensing machine-learning. In the cold, nutrient-rich surface waters, a subsiding spring bloom was associated with elevated PP, BP, and BA alongside a high temperature sensitivity (Q10) that indicates active microbial turnover. In contrast, the warm Atlantic-influenced waters exhibit a relatively lower PP but moderate cell-specific BP, suggesting bacterial maintenance metabolism under pre-bloom conditions. Notably, bacterial respiration (BR) estimates differed by 5- to 80-fold between the Winkler and in vivo INT methods. Although the true BR likely lies between these estimates, our results highlight the substantial microbial activity and underscore the need for more accurate BR measurements in Arctic studies.
Continue reading ‘Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait’Ocean acidification changes diet effects and differentially impacts two populations of red abalone (Haliotis rufescens)
Published 14 July 2026 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, mollusks, morphology, mortality, multiple factors, nutrients, otherprocess, performance, reproduction
Absorption of CO2 by global oceans is decreasing pH resulting in ocean acidification (OA). Impacts on shellfish have been documented in ecologically and commercially important species. We examined the influence of diet and OA between two populations of red abalone (Haliotis rufescens) a species of aquaculture importance and declining wild populations. Populations experience different exposure histories: strong upwelling (Van Damme, California [VD]) historically exposed to low-pH conditions and weak-intermittent upwelling (Santa Barbara, California [SB]). Abalone were cultured under control-pH or OA-conditions and fed crustose coralline algae (CCA) or diatoms used in aquaculture. We tested treatment effects of population, settlement diet, and OA-exposure on survival as influenced by larval-energy stores. Survival in both populations was enhanced by CCA when cultured under both treatment conditions; however, by later stages, this effect remained only for SB. SB had reduced post-settlement survival when cultured under OA-conditions, whereas post-settlement survival of VD was not. Diet affected the relationship between larval-energy and post-settlement survival; a positive relationship when fed diatoms and a negative relationship with CCA. The relationship between larval energy and post-settlement survival was stronger in VD. CCA enhanced juvenile growth in SB cultured abalone at both three-months and one-year post-settlement. Settlement diets can reduce the impacts of OA on early-life stages of abalone, but population differences driven by underlying energetics affect the consistency of this outcome. These findings illuminate the impacts from OA, suggesting populations may be at risk, and inform strategies for developing and sustaining shellfish aquaculture in the face of changing ocean conditions.
Continue reading ‘Ocean acidification changes diet effects and differentially impacts two populations of red abalone (Haliotis rufescens)’Brown algae as winners: divergent resilience to high light under acidified conditions shapes macroalgal communities around a carbon dioxide vent
Published 14 July 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, field, laboratory, light, multiple factors, North Pacific, otherprocess, physiology, vents
To investigate the effects of ocean acidification (OA) on macroalgae, we conducted in situ surveys along a natural CO2 vent gradient in Shikine Island, Japan, together with complementary laboratory culture experiments. The in-situ surveys revealed that near the CO2 vent (where pH dropped by 0.37), macroalgal diversity and species-richness were less than half those at the reference sites under ambient pH conditions. Nevertheless, the rates of CO2 assimilation of several common macroalgae increased from the reference site to the areas near the CO2 vent. This enhancement coincided with decreased photosynthetic CO2 affinity, reflecting that the acidified area down-regulated CO2-concentrating mechanisms in the algae. Measured photosystem II activity revealed that macroalgae at reference sites had lower electron transport rate and light utilization efficiency. The laboratory culture experiments, in which the dominant species (Gelidium elegans and Dictyopteris undulata), were cross-exposed to ambient and elevated CO2 conditions, further demonstrated that the stress near the CO2 vent significantly exacerbated photoinhibition under high light stress. Our results demonstrate that reduced pH and high sunlight act synergistically to impair macroalgal photosynthesis through exacerbated photoinhibition. This effect was more pronounced in red algae (e.g., G. elegans) than in brown algae (e.g., D. undulata). These different physiological responses provide a mechanistic explanation for an observed community shift, from red algal dominance in ambient pCO2 areas to brown algal dominance near the vent. Our findings imply that future OA, when combined with high-light stress, may selectively disadvantage high-light-sensitive species, thereby altering macroalgal community structure in coastal waters.
Continue reading ‘Brown algae as winners: divergent resilience to high light under acidified conditions shapes macroalgal communities around a carbon dioxide vent’Climate assessment report for the Central Arctic Ocean (CAO) [Suppl. to ICES Scientific Reports 8(25)]
Published 9 July 2026 Science ClosedTags: Arctic, chemistry, community composition, fish, mammals, zooplankton
Climate change is transforming the Central Arctic Ocean (CAO) at an unprecedented pace. Sea ice is rapidly declining in extent, thickness, and age, with projections indicating an ice-free summer Arctic by mid-century, possibly earlier. This loss of ice amplifies warming, alters stratification and circulation, and accelerates ocean acidification—occurring up to four times faster than the global average—threatening calcifying organisms and ecosystem stability.
Biological impacts are profound: shifts in microbial and primary producer communities, reduced ice-associated biodiversity, and boreal species moving northward disrupt food webs. Benthic ecosystems show signs of long-term decline in biodiversity and organic carbon supply, while fish, seabirds, and marine mammals face habitat loss, changing prey availability, and new stressors such as increased predation and contaminants. Some species may benefit from enhanced productivity, but cumulative effects of warming, acidification, and ice loss remain uncertain. These changes interact with other pressures—pollution, invasive species, and human activities—creating complex, compounding stress on the CAO ecosystem. Knowledge gaps on tipping points and resilience underscore the urgent need for research on circulation, carbon dynamics, and species adaptation to inform conservation and management strategies.
Continue reading ‘Climate assessment report for the Central Arctic Ocean (CAO) [Suppl. to ICES Scientific Reports 8(25)]’Physical-chemical gradients, CO2 venting dynamics and microbial community composition in a shallow Mediterranean CO2-rich hydrothermal system
Published 19 June 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, Mediterranean, otherprocess, physiology, prokaryotes, vents
Shallow-water CO2-rich hydrothermal systems provide natural laboratories for studying localized ocean acidification under realistic environmental conditions. Here, we present a multidisciplinary characterization of the Calent mound CO2-rich system (Columbretes Islands, Western Mediterranean), based on oceanographic surveys conducted in 2020 and 2021. Localized pH anomalies were detected directly above active vents, reaching maximum reductions of 1.12 pH units, whereas water-column temperature anomalies were minimal and subsurface sediment temperatures exceeded ambient seawater by 5.67 °C. Gas analyses indicated high CO2 concentrations (0.094 ± 0.008 mol L− 1), with heterogeneous degassing regimes, ranging from sporadic to continuous emissions and an average flux of 189.4 ± 15.4 kg CO2 m− 2 yr− 1 at the active vent field. Vent fluids were significantly enriched in dissolved inorganic nutrients, particularly silicate, phosphate, nitrate+nitrite, and ammonium. Benthic microbial mats hosted metabolically diverse prokaryotic and eukaryotic communities, including hydrothermal-associated taxa such as Zetaproteobacteria, Campylobacterota, and Nitrosophaeria, consistent with iron, sulfur, and ammonia oxididation metabolisms. Several microbial core taxa persisted across years despite shifts in relative abundance. These findings demonstrate that Calent mound sustains an intense yet highly localized biogeochemical environment within the photic zone, where CO2 venting and nutrient inputs jointly influence carbonate chemistry and microbial community structure.
Continue reading ‘Physical-chemical gradients, CO2 venting dynamics and microbial community composition in a shallow Mediterranean CO2-rich hydrothermal system’Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification
Published 18 June 2026 Science ClosedTags: algae, annelids, biological response, BRcommunity, bryozoa, cnidaria, community composition, corals, crustaceans, echinoderms, fish, Indian, laboratory, mollusks, morphology, North Pacific, otherprocess, physiology, vents
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’Shifts of tentacles-associated prokaryotes of Anemonia viridis along a natural pH gradient
Published 18 June 2026 Science ClosedTags: 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 ClosedTags: 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 ClosedTags: 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 ClosedTags: 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’
