Increasingly frequent large-scale pelagic Sargassum algae blooms in the Atlantic have become a problem for coastal ecosystems. The mass decay of these blooms reduces water quality for coastal flora and fauna. However, the effects of living Sargassum blooms on seawater quality and consequently coral reef ecosystems that rely on delicately balanced carbonate chemistry are more ambiguous. Future oceans are predicted to be more acidic as additional anthropogenic CO2 emissions are absorbed, potentially tipping the balance in favor of algal blooms at the cost of coral survival. This study aimed to simulate the indirect interaction between pelagic Sargassum spp. and Acropora cervicornis coral fragments from the Florida Reef in current-day and future ocean pH conditions over the course of 70 days in a mesocosm experimental system. Measurements of coral growth and health via buoyant weight and Pulse Amplitude Modulated (PAM) fluorescence measurements reveal an unexpected coral-algal interaction. After 1 month, coral growth was significantly reduced under ocean acidification conditions and exposure to Sargassum; at the same time quantum yield and maximum electron transport rate of photosynthesis were increased relative to control counterparts in ambient and future pH scenarios by up to 14% and 18% respectively. These improvements in photosynthetic efficiency did not translate to significant differences in growth by the final measurement time point. In addition, the presence of Sargassum spp. did not raise seawater pH in the system, raising questions about how it benefited photosynthetic efficiency in exposed corals. Heterotrophy of detrital algal matter is suspected to compensate for impaired photosynthesis of pH stressed corals. Therefore, despite their current negative reputation, Sargassum blooms could provide short term localized benefits to corals in present and future ocean conditions.
Continue reading ‘Quantifying coral-algal interactions in an acidified ocean: Sargassum spp. exposure mitigates low pH effects on Acropora cervicornis health’Posts Tagged 'mesocosms'
Quantifying coral-algal interactions in an acidified ocean: Sargassum spp. exposure mitigates low pH effects on Acropora cervicornis health
Published 3 March 2025 Science ClosedTags: algae, biological response, BRcommunity, corals, growth, laboratory, mesocosms, North Atlantic, physiology
Effect of seawater acidification on energy metabolism in the hydrocoral Millepora alcicornis: inhibition of citrate synthase activity indicates disruption in aerobic pathways
Published 10 February 2025 Science ClosedTags: biological response, cnidaria, laboratory, mesocosms, physiology, South Atlantic
Ocean acidification is a major threat to coral reefs worldwide, with reduced growth already reported in the hydrocoral Millepora alcicornis (Linnaeus, 1758) under these conditions. Inhibition of enzymes related to energy metabolism is hypothesized as one of the mechanisms associated with the physiological impacts of ocean acidification. Therefore, a mesocosm experiment was conducted to investigate whether three levels of decreasing seawater pH could alter the activity of key enzymes involved in the energy metabolism in M. alcicornis. Hydrocorals were acclimated to marine mesocosm conditions for 20 days and then exposed to different seawater pH levels [ambient pH (8.1) and experimental pH (7.8, 7.5 and 7.2)] for 16 and 30 days. Endpoints analyzed included the activity of key enzymes involved in the regulation of the glycolytic pathway (hexokinase and pyruvate kinase), aerobic energy production via the Krebs cycle (citrate synthase) and anaerobic energy production via lactate formation (lactate dehydrogenase). The results obtained show that only citrate synthase was affected by seawater acidification, as a marked reduction in its activity was observed at all experimental pH levels tested (7.8, 7.5 and 7.2). This finding indicates that reduced growth previously reported for M. alcicornis under seawater acidification conditions can be explained, at least in part, by a negative impact on the Krebs cycle, a major pathway involved in aerobic energy production.
Continue reading ‘Effect of seawater acidification on energy metabolism in the hydrocoral Millepora alcicornis: inhibition of citrate synthase activity indicates disruption in aerobic pathways’Seagrass influence on mitigating ocean acidification and warming impacts on tropical calcifying macroalgae
Published 28 January 2025 Science ClosedTags: algae, biological response, BRcommunity, laboratory, mesocosms, mitigation, multiple factors, phanerogams, temperature
Highlights
- OA and warming reduce calcium carbonate for marine calcifiers.
- Seagrass can capture excess carbon, possibly mitigating OA effects.
- 12-week study tested algae with/without seagrass under increasing stress.
- M. rosea was affected by OA and warming; H. opuntia by temperature alone.
- Mesophyllum sp. was resilient, and seagrass did not reduce OA impacts.
- Light, flow, combining OA and warming, likely to impact coralline algae
Abstract
Ocean acidification (OA) and warming pose significant threats to marine ecosystems, particularly by reducing calcium carbonate availability for marine calcifiers. Given that seagrasses can capture and store excess carbon, this study aimed to investigate whether seagrasses can mitigate the impacts of OA and elevated temperatures on three calcifying macroalgae: Mastophora rosea, Halimeda opuntia, and Mesophyllum sp. A 12-week mesocosm experiment was conducted, where the algae were cultured with and without seagrass under gradually increasing stress conditions: ambient conditions, OA alone for four weeks, OA combined with elevated (but non-stressful) temperatures (28°C) for four weeks, and OA plus a stress-inducing temperature (31°C) for two weeks. Results indicated that OA and warming negatively affected M. rosea, while H. opuntia was more strongly impacted by temperature alone. Mesophyllum sp. exhibited resilience to both OA and elevated temperatures. Contrary to expectations, the presence of seagrass did not mitigate the negative effects of OA and warming on these calcifying macroalgae species.
Continue reading ‘Seagrass influence on mitigating ocean acidification and warming impacts on tropical calcifying macroalgae’The impact of climate change stressors on microbial respiration and community structure: ocean acidification and artificial upwellling
Published 14 January 2025 Science ClosedTags: biological response, BRcommunity, community composition, field, mesocosms, multiple factors, North Atlantic, nutrients, otherprocess, physiology, phytoplankton, prokaryotes, respiration
Microbial community respiration significantly influences the oceans capacity to sequester CO2 in marine ecosystems. Despite its pivotal role, there remains limited understanding of the variability and magnitude of community respiration in marine ecosystems, especially regarding its sensitivity to climate change stressors. This knowledge gap hinders a comprehensive grasp of its contribution to the global carbon cycle. Traditional in situ approaches for measuring community respiration are subject to several methodological limitations, particularly that of sensitivity in oligotrophic ecosystems, which cover more than 40% of the Earth’s ocean surface. These limitations thus contribute significantly to the uncertainty in global estimates of carbon budgets. To address these challenges, enzymatic techniques such as ETSvitro offer a fast and sensitive method to assess respiratory activity rates at spatial scales that are difficult to cover using conventional approaches. The method involves reducing the tetrazolium salt, INT, within the respiratory chain under substrate saturation levels (i.e., NADH, NADPH, and succinate). However, the reliability of the ETSvitro method has been questioned because it measures potential respiratory activity rather than actual respiration. In response to these concerns, another enzymatic technique, ETSvivo, emerged presumably as a more realistic estimate of actual respiration. Unlike ETSvitro, ETSvivo measures INT under in vivo conditions, utilizing substrates naturally available inside the cell. Nevertheless, before these methods can be considered feasible proxies for community respiration, further evaluation is needed to determine their universal applicability in marine ecosystems. In this thesis, our objective was to improve our understanding of community respiration by addressing its methodological limitations and investigating the drivers responsible for its variability. We paid particular attention to planktonic community structure and the impact of two climate change stressors: ocean acidification and changes in nutrient fertilization. Simulating a typical ETSvivo assay in eight independent experiments using surface coastal and open ocean waters from the Canary region, we observed that INT alone significantly influences the physiological status of bacteria. Bacteria are considered the primary contributors to respiration in oligotrophic environments, but their physiological status is largely affected by the inherent toxicity of INT. Consequently, we question the applicability of the ETSvivo method as a proxy for community respiration in oligotrophic regions. On the other hand, we explore the temporal variability of respiratory metabolism through two mesocosm experiments conducted in the oligotrophic waters of the subtropical Eastern North Atlantic. In the first mesocosms experiment, we investigated the impact of changing community structure and biomass on the temporal variability of community respiration measured through the Winkler method (R), ETS activity, and their ratio (R/ETS) in response to increasing CO2 concentrations and nutrient fertilization (e.g., due to local upwelling events). Our results suggest that community respiration and ETS activity do not respond to CO2 during oligotrophic conditions. However, following fertilization, community respiration increased in the two high CO2 mesocosms coinciding with an increase in microplankton, primarily diatoms. Simultaneously, the R/ETS ratio showed no correlation with community structure or biomass, indicating its variability makes it unsuitable for application with communities undergoing abrupt changes in trophic conditions. In light of these findings, the second mesocosm experiment explored the influence of different upwelling intensities and frequencies (singular pulse versus recurring upwelling) on community respiration. Our results demonstrate that community respiration is sensitive to changes in upwelling intensities but more significantly to the mode in which nutrients are supplied to oligotrophic waters. The planktonic community structure significantly influenced the observed variability in community respiration, revealing notable differences under varying upwelling intensities.The results of this thesis underscore the significance of mitigating methodological uncertainties to achieve precise measurements of respiration rates. It is crucial to adequately assess the impact of climate change-induced stressors, especially ocean acidification and changes in nutrient fertilization, along with planktonic community structure, as drivers of temporal variability. This thorough examination is essential for gaining a deeper understanding and, consequently, making more accurate predictions of community respiration in marine ecosystems.
Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes
Published 9 January 2025 Science ClosedTags: biogeochemistry, biological response, laboratory, mesocosms, morphology, multiple factors, North Atlantic, phanerogams, physiology, primary production, respiration, temperature
Highlights
- 45-days mesocosm experiment with whole-benthic community to mimic nature conditions
- Global warming (GW) and ocean acidification (OA) modify C dynamics on seagrasses.
- OA enhances GPP and NCP and synergistic effects when combined with GW.
- DOC production decreased with OA and GW separately, but increased when combined.
- Climate change potentially increases the blue carbon service of C. nodosa populations.
Abstract
Ocean acidification (OA) and global warming (GW) drive a variety of responses in seagrasses that may modify their carbon metabolism, including the dissolved organic carbon (DOC) fluxes and the organic carbon stocks in upper sediments. In a 45-day full-factorial mesocosm experiment simulating forecasted CO2 and temperature increase in a Cymodocea nodosa community, we found that net community production (NCP) was higher under OA conditions, particularly when combined with warming (i.e., synergistic effect). Moreover, under OA conditions, an increase in aboveground biomass and photosynthetic shoot area was recorded. Interestingly, DOC fluxes were reduced when exposed to OA; however, an increase occurred when both factors acted together (i.e., antagonistic effect), which was attributable to increased DOC release by plants. Our results suggest that C. nodosa populations in temperate latitude may favor blue carbon service in future scenarios of OA and GW by increasing the NCP, the DOC export with lower labile:recalcitrant ratio, and accumulating more organic carbon in upper sediments. These findings offer additional arguments for the urgent need to protect and conserve this valuable ecosystem.
Continue reading ‘Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes’Resource homogenisation drives niche convergence between generalists and specialists in a future ocean
Published 13 December 2024 Science ClosedTags: algae, biological response, community composition, laboratory, mesocosms, multiple factors, otherprocess, prokaryotes, temperature
Highlights
- Do marine herbivores adjust their trophic niches under climate change?.
- Specialist and generalist herbivore niches and their food were tested using stable isotopes.
- Food resources were dominated by turf algae and SOM under climate change.
- Niche breath of generalists narrowed under climate stress but widened in specialists.
- Generalists and specialists appear to converge their trophic niches under climate change.
Abstract
When humans drive rapid environmental change, is it favourable to be a generalist or specialist? To address this question, we compare how specialist and generalist marine herbivores adjust their isotopic niches (used as proxy for trophic niche) in response to predicted resource alterations under the simulated effects of ocean warming and acidification (based on a 6-month mesocosm experiment). Here, we show that when exposed to multiple climate stressors, food resources homogenized towards dominance of turf algae and suspended organic matter, with generalists and specialists adjusting their trophic niches in opposing ways. Whilst the niche breath of most generalists narrowed under climate stressors, those of specialists generally broadened, causing increasing overlap between their niches. The magnitude of this change was such that some generalists turned into specialists, and vice versa. Under ocean acidification, there was a greater probability of generalists increasing and specialists maintaining their biomass, respectively, but under warming the biomass of both specialists and generalists had a greater probability of collapse. For specialists, this collapse occurred even though they had adequate thermal tolerance and the capacity to expand their trophic niche. Climate change constrains or liberates resources, but where they are homogenized, generalists and specialists are likely to converge their trophic niches so they can exploit transforming environments for their survival or adaptive advantage.
Continue reading ‘Resource homogenisation drives niche convergence between generalists and specialists in a future ocean’Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability
Published 6 December 2024 Science ClosedTags: adaptation, biological response, calcification, corals, field, laboratory, mesocosms, molecular biology, otherprocess, photosynthesis, physiology, South Pacific
Corals residing in habitats that experience high-frequency seawater pCO2 variability may possess an enhanced capacity to cope with ocean acidification, yet we lack a clear understanding of the molecular toolkit enabling acclimatisation to environmental extremes or how life-long exposure to pCO2 variability influences biomineralisation. Here, we examined the gene expression responses and micro-skeletal characteristics of Pocillopora damicornis originating from the reef flat and reef slope of Heron Island, southern Great Barrier Reef. The reef flat and reef slope had similar mean seawater pCO2, but the reef flat experienced twice the mean daily pCO2 amplitude (range of 797 v. 399 μatm day−1, respectively). A controlled mesocosm experiment was conducted over 8 weeks, exposing P. damicornis from the reef slope and reef flat to stable (218 ± 9) or variable (911 ± 31) diel pCO2 fluctuations (μatm; mean ± SE). At the end of the exposure, P. damicornis originating from the reef flat demonstrated frontloading of 25% of the expressed genes regardless of treatment conditions, suggesting constitutive upregulation. This included higher expression of critical biomineralisation-related genes such as carbonic anhydrases, skeletal organic matrix proteins, and bicarbonate transporters. The observed frontloading corresponded with a 40% increase of the fastest deposited areas of the skeleton in reef flat corals grown under non-native, stable pCO2 conditions compared to reef slope conspecifics, suggesting a compensatory response that stems from acclimatisation to environmental extremes and/or relief from stressful pCO2 fluctuations. Under escalating ocean warming and acidification, corals acclimated to environmental variability warrant focused investigation and represent ideal candidates for active interventions to build reef resilience while societies adopt strict policies to limit climate change.
Continue reading ‘Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability’The influence of macrophytes on diurnal pH variability in subtropical estuaries: a mesocosm study
Published 4 December 2024 Science ClosedTags: algae, biological response, BRcommunity, chemistry, Indian, laboratory, mesocosms, phanerogams
Highlights
- Macrophytes influence estuary water column pH levels.
- Floating macrophytes decrease pH and submerged macrophytes increase pH.
- Diurnal pH variability is more pronounced in submerged macroalgae.
- Floating macrophytes exhibit lower diurnal variability.
Abstract
Coastal ecosystems are increasingly threatened by anthropogenic impacts, particularly from land-based activities that drive eutrophication. This research investigated eutrophication and the unique challenges facing southern hemisphere coastal ecosystems. We used a mesocosm study to measure the influence of a macroalga (Rhizoclonium riparium) and a floating macrophyte (Pistia stratiotes), on diurnal pH variability. Diurnal pH variability was more pronounced in the presence of macroalgae due to the direct release of metabolic byproducts into the water column during photosynthesis and respiration. In contrast, floating macrophyte treatments had lower diurnal pH variability, as metabolic byproducts are released into the atmosphere through floating foliage. Floating macrophytes influenced overall water column pH levels, resulting in an acidification effect, becoming more pronounced as macrophyte biomass increased. The study highlighted the importance of nutrient management and its association with macrophytes, to preserve the delicate balance of estuaries, and ensure the sustainable functioning of these critical ecosystems. Further in situ research is recommended to validate and expand on the mesocosm findings.
Continue reading ‘The influence of macrophytes on diurnal pH variability in subtropical estuaries: a mesocosm study’Seawater warming rather than acidification profoundly affects coastal geochemical cycling mediated by marine microbiome
Published 28 November 2024 Science ClosedTags: BRcommunity, community composition, laboratory, mesocosms, molecular biology, multiple factors, otherprocess, prokaryotes, sediment, temperature
Highlights
- The structure and function of coastal microbial communities are influenced by ocean warming and acidification.
- Elevated temperature more profoundly impacts microbial communities than does acidification.
- Warming promotes denitrification that may increase nitrogen loss.
- The nitrogen, sulfur cycles, and carbon-fixation pathways exhibit distinct variation patterns under warming.
Abstract
The most concerning consequences of climate change include ocean acidification and warming, which can affect microbial communities and thus the biogeochemical cycling they mediate. Therefore, it is urgent to study the impact of ocean acidification and warming on microbial communities. In the current study, metagenomics was utilized to reveal how the structure and function of marine microorganisms respond to ocean warming and acidification. In terms of community structure, Non-metric Multidimensional Scaling analysis visualized the similarity or difference between the control and the warming or acidification treatments, but the inter-group differences were not significant. In terms of gene functionality, warming treatments showed greater effects on microbial communities than acidification. After treatment with warming, the relative abundance of genes associated with denitrification increased, suggesting that ocean nitrogen loss can increase with increased temperature. Conversely, acidification treatments apparently inhibited denitrification. Warming treatment also greatly affected sulfur-related microorganisms, increasing the relative abundance of certain sulfate-reducing prokaryote, and enriched microbial carbon-fixation pathways. These results provide information on the response strategies of coastal microorganisms in the changing marine environments.
Continue reading ‘Seawater warming rather than acidification profoundly affects coastal geochemical cycling mediated by marine microbiome’Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification
Published 31 October 2024 Science ClosedTags: biological response, BRcommunity, calcification, community composition, corals, laboratory, mesocosms, mitigation, molecular biology, mortality, multiple factors, otherprocess, temperature
Significance
Coral reefs are exceptional ecosystems and support hundreds of millions of people around the world, yet they are under severe threat due to ocean warming and acidification. Reefs are predicted to collapse over the next few decades under these climate change stressors, with grave consequences for society. Contrary to predictions of near total destruction, this study shows that with effective climate change mitigation, coral reefs will continue to change, but global reef collapse may still be avoidable.
Abstract
Coral reefs are among the most sensitive ecosystems affected by ocean warming and acidification, and are predicted to collapse over the next few decades. Reefs are predicted to shift from net accreting calcifier-dominated systems with exceptionally high biodiversity to net eroding algal-dominated systems with dramatically reduced biodiversity. Here, we present a two-year experimental study examining the responses of entire mesocosm coral reef communities to warming (+2 °C), acidification (−0.2 pH units), and combined future ocean (+2 °C, −0.2 pH) treatments. Contrary to modeled projections, we show that under future ocean conditions, these communities shift structure and composition yet persist as novel calcifying ecosystems with high biodiversity. Our results suggest that if climate change is limited to Paris Climate Agreement targets, coral reefs could persist in an altered state rather than collapse.
Continue reading ‘Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification’Shifting seagrass-oyster interactions alter species response to ocean warming and acidification
Published 16 October 2024 Science ClosedTags: biological response, BRcommunity, community composition, mesocosms, mollusks, morphology, multiple factors, otherprocess, phanerogams, physiology, temperature
- A major challenge in biodiversity research is the incorporation of species interactions into frameworks describing population and community response to global edfnmental change (GEC). Mutualisms are a type of species interaction especially sensitive to changing environmental conditions, and the breakdown of facilitative species interactions could amplify the negative impacts of novel climate regimes on focal species.
- Here, we investigate how reciprocal interactions between two coastal foundation species, the eastern oyster (Crassostrea virginica) and eelgrass (Zostera marina) shift in sign and magnitude in response to ocean warming (+1.5°C) and acidification (−0.4 pH) via a manipulative co-culture experiment in mesocosms.
- Under ambient environmental conditions, oysters facilitated eelgrass leaf growth and clonal reproduction by 35% and 38%, respectively. Simultaneously, eelgrass decreased the oyster condition index (the ratio of tissue to shell biomass) by 35%, indicating greater allocation of energy to shell growth instead of soft tissues at ambient conditions. Varying sensitivities of each species to ocean warming and/or acidification treatments led to complex shifts in species interactions that were trait dependent. As such, community outcomes under future conditions were influenced by species interactions that amplified and mitigated species response to environmental change.
- Synthesis: Given that species interaction effect sizes were similar in magnitude to effect sizes of warming or pH treatments, our results underscore the need to identify key species and interaction types that strongly influence community response to GEC. Specifically, for macrophyte-bivalve interactions, understanding how physiological limitations on growth are impacted by environmental heterogeneity and co-culture will support the successful restoration of natural populations and the rapid expansion of aquaculture.
Shifting seagrass-oyster interactions alter species response to ocean warming and acidification
Published 30 September 2024 Science ClosedTags: algae, biological response, BRcommunity, mesocosms, mollusks, morphology, physiology
- A major challenge in biodiversity research is the incorporation of species interactions into frameworks describing population and community response to global edfnmental change (GEC). Mutualisms are a type of species interaction especially sensitive to changing environmental conditions, and the breakdown of facilitative species interactions could amplify the negative impacts of novel climate regimes on focal species.
- Here, we investigate how reciprocal interactions between two coastal foundation species, the eastern oyster (Crassostrea virginica) and eelgrass (Zostera marina) shift in sign and magnitude in response to ocean warming (+1.5°C) and acidification (−0.4 pH) via a manipulative co-culture experiment in mesocosms.
- Under ambient environmental conditions, oysters facilitated eelgrass leaf growth and clonal reproduction by 35% and 38%, respectively. Simultaneously, eelgrass decreased the oyster condition index (the ratio of tissue to shell biomass) by 35%, indicating greater allocation of energy to shell growth instead of soft tissues at ambient conditions. Varying sensitivities of each species to ocean warming and/or acidification treatments led to complex shifts in species interactions that were trait dependent. As such, community outcomes under future conditions were influenced by species interactions that amplified and mitigated species response to environmental change.
- Synthesis: Given that species interaction effect sizes were similar in magnitude to effect sizes of warming or pH treatments, our results underscore the need to identify key species and interaction types that strongly influence community response to GEC. Specifically, for macrophyte-bivalve interactions, understanding how physiological limitations on growth are impacted by environmental heterogeneity and co-culture will support the successful restoration of natural populations and the rapid expansion of aquaculture.
Long-term study of the combined effects of ocean acidification and warming on the mottled brittle star Ophionereis fasciata
Published 27 September 2024 Science ClosedTags: biological response, BRcommunity, calcification, dissolution, echinoderms, growth, mesocosms, mortality, multiple factors, physiology, respiration, temperature
The global ocean is rapidly changing, posing a substantial threat to the viability of marine populations due to the co-occurrence of multiple drivers, such as ocean warming (OW) and ocean acidification (OA). To persist, marine species must undergo some combination of acclimation and adaptation in response to these changes. Understanding such responses is essential to measure and project the magnitude and direction of current and future vulnerabilities in marine ecosystems. Echinoderms have been recognised as a model in studying of OW-OA effects on marine biota. However, despite their global diversity, vulnerability, and ecological importance in most marine habitats, brittle stars (ophiuroids) are poorly studied. A long-term mesocosm experiment was conducted on adult mottled brittle star (Ophionereis fasciata) as a case study to investigate the physiological response and trade-offs of marine organisms to ocean acidification, ocean warming and the combined effect of both drivers. Long-term exposure of O. fasciata to high temperature and low pH affected survival, respiration and regeneration rates, growth rate, calcification/dissolution, and righting response. Higher temperatures increased stress and respiration and decreased regeneration and growth rates as well as survival. Conversely, changes in pH had more subtle or no effect affecting only respiration and calcification. Our results indicate that exposure to a combination of high temperature and low pH produces complex responses for respiration, righting response and calcification. We address the knowledge gap of the impact of a changing ocean on ophiuroids in the context of echinoderm studies, proposing this class as an ideal alternative echinoderm for future research.
Continue reading ‘Long-term study of the combined effects of ocean acidification and warming on the mottled brittle star Ophionereis fasciata’Widespread scope for coral adaptation under combined ocean warming and acidification
Published 27 September 2024 Science ClosedTags: biological response, BRcommunity, calcification, corals, mesocosms, molecular biology, mortality, multiple factors, North Pacific, temperature
Reef-building coral populations are at serious risk of collapse due to the combined effects of ocean warming and acidification. Nonetheless, many corals show potential to adapt to the changing ocean conditions. Here we examine the broad sense heritability (H2) of coral calcification rates across an ecologically and phylogenetically diverse sampling of eight of the primary reef-building corals across the Indo-Pacific. We show that all eight species exhibit relatively high heritability of calcification rates under combined warming and acidification (0.23–0.56). Furthermore, tolerance to each factor is positively correlated and the two factors do not interact in most of the species, contrary to the idea of trade-offs between temperature and pH sensitivity, and all eight species can co-evolve tolerance to elevated temperature and reduced pH. Using these values together with historical data, we estimate potential increases in thermal tolerance of 1.0–1.7°C over the next 50 years, depending on species. None of these species are probably capable of keeping up with a high global change scenario and climate change mitigation is essential if reefs are to persist. Such estimates are critical for our understanding of how corals may respond to global change, accurately parametrizing modelled responses, and predicting rapid evolution.
Continue reading ‘Widespread scope for coral adaptation under combined ocean warming and acidification’Key benthic species are affected by predicted warming in winter but show resistance to ocean acidification
Published 20 September 2024 Science ClosedTags: algae, biological response, BRcommunity, community composition, laboratory, mesocosms, mollusks, mortality, multiple factors, otherprocess, photosynthesis, physiology, temperature
The effects of climate change on coastal biodiversity are a major concern because altered community compositions may change associated rates of ecosystem functioning and services. Whilst responses of single species or taxa have been studied extensively, it remains challenging to estimate responses to climate change across different levels of biological organisation. Studies that consider the effects of moderate realistic near-future levels of ocean warming and acidification are needed to identify and quantify the gradual responses of species to change. Also, studies including different levels of biological complexity may reveal opportunities for amelioration or facilitation under changing environmental conditions. To test experimentally for independent and combined effects of predicted near-future warming and acidification on key benthic species, we manipulated three levels of temperature (winter ambient, +0.8 and +2°C) and two levels of pCO2 (ambient at 450 ppm and elevated at 645 ppm) and quantified their effects on mussels and algae growing separately and together (to also test for inter-specific interactions). Warming increased mussel clearance and mortality rates simultaneously, which meant that total biomass peaked at +0.8°C. Surprisingly, however, no effects of elevated pCO2 were identified on mussels or algae. Moreover, when kept together, mussels and algae had mutually positive effects on each other’s performance (i.e. mussel survival and condition index, mussel and algal biomass and proxies for algal productivity including relative maximum electron transport rate [rETRmax], saturating light intensity [Ik] and maximum quantum yield [Fv/Fm]), independent of warming and acidification. Our results show that even moderate warming affected the functioning of key benthic species, and we identified a level of resistance to predicted ocean acidification. Importantly, we show that the presence of a second functional group enhanced the functioning of both groups (mussels and algae), independent of changing environmental conditions, which highlights the ecological and potential economic benefits of conserving biodiversity in marine ecosystems.
Continue reading ‘Key benthic species are affected by predicted warming in winter but show resistance to ocean acidification’Toward an ecologically realistic experimental system to investigate the multigenerational effects of ocean warming and acidification on benthic invertebrates
Published 19 July 2024 Science ClosedTags: biological response, BRcommunity, chemistry, Mediterranean, mesocosms, methods, mollusks, North Atlantic
Human activities over the past 150 yr have led to significant carbon dioxide (CO2) emissions, causing global warming and ocean acidification. Surface ocean temperature has risen by 0.93°C since 1850, with projections of an additional +1.42°C to 3.47°C by 2080–2099. Ocean acidification, driven by CO2 absorption, has already lowered seawater pH by 0.1 units, affecting calcifying organisms, including shelled mollusks. Long-term multigenerational studies on mollusk responses to both ocean acidification and warming, under realistic environmental conditions, are scarce. To address this knowledge gap, two mobile experimental units that can be deployed at the vicinity of shellfish farming areas were developed within the framework of the CocoriCO2 project. The experimental systems were designed to manipulate temperature and pH as offsets from ambient conditions. The experimental units have shown their effectiveness in terms of controlling and maintaining pH and temperature to assess the multigenerational effects of ocean warming and acidification on benthic invertebrates. Finally, the developed experimental systems can be modified easily to provide an educated assessment of the impact of other relevant environmental changes such as deoxygenation and changes in salinity.
Continue reading ‘Toward an ecologically realistic experimental system to investigate the multigenerational effects of ocean warming and acidification on benthic invertebrates’“Quantifying the Impacts of Multiple Stressors” (QIMS)—a new experimental platform for robust multifactorial experiments in benthic ecosystems
Published 16 July 2024 Science ClosedTags: chemistry, laboratory, mesocosms, methods, multiple factors, temperature
To predict the ecological consequences of expected global change, we need to understand the independent and combined effects of multiple stressors. Multiple experimental treatments are required to simultaneously test for effects of multiple stressors at different levels of intensity, independently and combined, and at different levels of biological organization. Most marine multiple stressors studies to date are conducted on assembled communities in mesocosms with a low number of treatments or low replication of treatments or both. These limitations prevent (1) robust data analyses, (2) characterization of single and combined effects of multiple stressors, and (3) identification of mechanisms underpinning biological responses. We present a new mesocosm-based experimental platform for benthic communities: Quantifying the Impacts of Multiple Stressors (QIMS). Here, 96 independent mesocosms facilitate multifactorial and multilevel experimental designs with the high replication required for robust tests of multiple stressors and biological interactions. For example, three distinct pH levels are achieved by manipulating CO2 concentrations in the air supply, and three water temperature levels are provided by a cooling system in a fully crossed design that is required to identify all potential interactions, from which all combinations can be replicated 10 times (i.e., 90 experimental units). We demonstrate clearly how different levels of temperature and pCO2/pH can be manipulated precisely and maintained for at least 7 weeks. QIMS complements the limited number of permanently installed marine mesocosm facilities worldwide that simulate ocean warming and/or acidification and expedites multiple stressor research by providing an unprecedented level of replication for statistical robustness.
Continue reading ‘“Quantifying the Impacts of Multiple Stressors” (QIMS)—a new experimental platform for robust multifactorial experiments in benthic ecosystems’Predictable patterns within the kelp forest can indirectly create temporary refugia from ocean acidification
Published 20 June 2024 Science ClosedTags: algae, biological response, BRcommunity, chemistry, dissolution, growth, mesocosms, mollusks, morphology, North Pacific
Highlights
- Potential of kelp as ocean acidification refugia has been addressed through an integration of observations, modelling and mesocosm work.
- Kelp did not have a direct mitigating effect against OA in the low retentive habitats.
- Improved biological responses were observed in investigated calcifiers.
- Positive responses were related to increased predictability in pH autocorrelation signal and improved habitat provisioning through resource utilization.
- Kelp can improve ecosystem services
Abstract
Kelps are recognized for providing many ecosystem services in coastal areas and considered in ocean acidification (OA) mitigation. However, assessing OA modification requires an understanding of the multiple parameters involved in carbonate chemistry, especially in highly dynamic systems. We studied the effects of sugar kelp (Saccharina latissima) on an experimental farm at the north end of Hood Canal, Washington—a low retentive coastal system. In this field mesocosm study, two oyster species (Magallana gigas, Ostrea lurida) were exposed at locations in the mid, edge, and outside the kelp array. The Hood Head Sugar Kelp Farm Model outputs were used to identify dominating factors in spatial and temporal kelp dynamics, while wavelet spectrum analyses helped in understanding predictability patterns. This was linked to the measured biological responses (dissolution, growth, isotopes) of the exposed organisms. Positioned in an area of high (sub)-diel tidal fluxes with low retention potential, there were no measurable alterations of the seawater pH at the study site, demonstrating that the kelp array could not induce a direct mitigating effect against OA. However, beneficial responses in calcifiers were still observed, which are linked to two causes: increased pH predictability and improved provisioning through kelp-derived particulate organic resource utilization and as such, kelp improved habitat suitability and indirectly created refugia against OA. This study can serve as an analogue for many coastal bay habitats where prevailing physical forcing drives chemical changes. Future macrophyte studies that investigate OA mitigating effects should focus also on the importance of predictability patterns, which can additionally improve the conditions for marine calcifiers and ecosystem services vulnerable to or compromised by OA, including aquaculture sustainability.
Continue reading ‘Predictable patterns within the kelp forest can indirectly create temporary refugia from ocean acidification’Macroalgal presence decreases coral calcification rates more than ocean acidification
Published 12 June 2024 Science ClosedTags: algae, biological response, BRcommunity, calcification, chemistry, corals, growth, laboratory, mesocosms, morphology, Red Sea
Global coral reef degradation has precipitated phase shifts toward macroalgal-dominated communities. Despite the negative repercussions for reefscapes, higher abundances of primary producers have the potential to positively impact the physicochemical environment and mitigate negative impacts of ocean acidification (OA). In this study, we investigated the influence of macroalgal (cf. Sargassum vulgare) density on coral (Acropora millepora and A. hemprichii) calcification rates under current and future OA conditions. Corals were resistant to OA up to ~ 1100 µatm, with no changes in calcification rates. However, the presence of (low and high density) algae reduced calcification rates by ~ 41.8%, suggesting either a chemical defense response due to algal metabolites or potential physical impacts from shading or abrasion. Documented beneficial buffering effects of macroalgae in OA may also elicit negative impacts on coral calcification, suggesting further work is needed to elucidate how species interactions influence responses to projected climate change.
Continue reading ‘Macroalgal presence decreases coral calcification rates more than ocean acidification’Ocean acidification alters microeukaryotic and bacterial food web interactions in a eutrophic subtropical mesocosm
Published 4 June 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, mesocosms, otherprocess, photosynthesis, phytoplankton, prokaryotes, zooplankton
Highlights
- The communities were strongly affected by phytoplankton bloom stages.
- Ocean acidification (OA) affected some taxa as the phytoplankton bloom stages progressed.
- OA changed the co-occurrence network complexity and stability of microeukaryotes.
- OA altered the proportions of potential interactions between phytoplankton and their predators.
Abstract
Ocean acidification (OA) is known to influence biological and ecological processes, mainly focusing on its impacts on single species, but little has been documented on how OA may alter plankton community interactions. Here, we conducted a mesocosm experiment with ambient (∼410 ppmv) and high (1000 ppmv) CO2 concentrations in a subtropical eutrophic region of the East China Sea and examined the community dynamics of microeukaryotes, bacterioplankton and microeukaryote-attached bacteria in the enclosed coastal seawater. The OA treatment with elevated CO2 affected taxa as the phytoplankton bloom stages progressed, with a 72.89% decrease in relative abundance of the protist Cercozoa on day 10 and a 322% increase in relative abundance of Stramenopile dominated by diatoms, accompanied by a 29.54% decrease in relative abundance of attached Alphaproteobacteria on day 28. Our study revealed that protozoans with different prey preferences had differing sensitivity to high CO2, and attached bacteria were more significantly affected by high CO2 compared to bacterioplankton. Our findings indicate that high CO2 changed the co-occurrence network complexity and stability of microeukaryotes more than those of bacteria. Furthermore, high CO2 was found to alter the proportions of potential interactions between phytoplankton and their predators, as well as microeukaryotes and their attached bacteria in the networks. The changes in the relative abundances and interactions of microeukaryotes between their predators in response to high CO2 revealed in our study suggest that high CO2 may have profound impacts on marine food webs.
Continue reading ‘Ocean acidification alters microeukaryotic and bacterial food web interactions in a eutrophic subtropical mesocosm’
