Turf algal prevalence will increase in coral ecosystems under ocean acidification yet their contribution towards the ongoing and projected degradation of reefs is often overlooked. Turf algal settlement was induced on exposed coral skeleton adjacent to live coral tissue to investigate coral-turf algal interactions through a combination of laboratory and field transplantation (shallow volcanic CO2 seep) experiments across two temperature regimes. Here, we show that turf algae are competitively favored over corals under high pCO2 conditions. Turf algae-associated biological activity locally acidified the microenvironment overlying the exposed coral skeleton, leading to its bioerosion. Increases in coral-turf algal interactions could shift coral ecosystems towards net dissolution and should be integrated into global accretion models when considering future carbonate budgets under climate change.
Continue reading ‘Turf algae drives coral bioerosion under high CO2’Posts Tagged 'corals'
Turf algae drives coral bioerosion under high CO2
Published 20 February 2024 Science ClosedTags: abundance, algae, biogeochemistry, biological response, BRcommunity, calcification, chemistry, communityMF, corals, dissolution, field, laboratory, morphology, multiple factors, North Pacific, otherprocess, photosynthesis, respiration, temperature, vents
Effects of year-long exposure to elevated pCO2 on the metabolism of back reef and fore reef communities
Published 16 February 2024 Science ClosedTags: abundance, biological response, BRcommunity, calcification, corals, dissolution, field, otherprocess, primary production, South Pacific
The implications of ocean acidification are acute for calcifying organisms, notably tropical reef corals, for which accretion generally is depressed and dissolution enhanced at reduced seawater pH. We describe year-long experiments in which back reef and fore reef (17-m depth) communities from Moorea, French Polynesia, were incubated outdoors under pCO2 regimes reflecting endpoints of representative concentration pathways (RCPs) expected by the end the century. Incubations were completed in three to four flumes (5.0 × 0.3 m, 500 L) in which seawater was refreshed and circulated at 0.1 m s−1, and the response of the communities was evaluated monthly by measurements of net community calcification (NCC) and net community productivity (NCP). For both communities, NCC (but not NCP) was affected by treatments and time, with NCC declining with increasing pCO2, and for the fore reef, becoming negative (i.e., dissolution was occurring) at the highest pCO2 (1067–1433 μatm, RCP8.5). There was scant evidence of community adjustment to reduce the negative effects of ocean acidification, and inhibition of NCC intensified in the back reef as the abundance of massive Porites spp. declined. These results highlight the risks of dissolution under ocean acidification for coral reefs and suggest these effects will be most acute in fore reef habitats. Without signs of amelioration of the negative effects of ocean acidification during year-long experiments, it is reasonable to expect that the future of coral reefs in acidic seas can be predicted from their current known susceptibility to ocean acidification.
Continue reading ‘Effects of year-long exposure to elevated pCO2 on the metabolism of back reef and fore reef communities’Assessment of warm-water coral reef tipping point thresholds
Published 29 January 2024 Science ClosedTags: biological response, corals, performance, review
Warm-water coral reefs are facing unprecedented Anthropogenic driven threats to their continued existence as biodiverse, functional ecosystems upon which hundreds of millions of people rely. Determining the tipping point thresholds of coral reef ecosystems requires robust assessment of multiple stressors and their interactive effects. We draw upon a literature search and the recent Global Tipping Points Revision initiative to consider warm-water coral reef ecosystem tipping point threshold sensitivity. Considering observed and projected stressor impacts we recognise a global mean surface temperature (relative to pre-industrial) tipping point threshold of 1.2 °C (range 0.7–1.5 °C) and an atmospheric CO2 warming threshold of 350 ppm (range 326–400 ppm), whilst acknowledging that interacting stressors, ocean warming response time, overshoot and cascading impacts have yet to be sufficiently assessed but are likely to lower this threshold. These uncertainties around tipping point sensitivities for such a crucially important ecosystem underlines the imperative of robust assessment and, in the case of knowledge gaps, employing a precautionary principle favouring the lower range tipping point values.
Continue reading ‘Assessment of warm-water coral reef tipping point thresholds’Biochemical adaptability of the relationship between tropical hard corals and photosynthetic symbiotic algae under climate change
Published 23 January 2024 Science ClosedTags: adaptation, algae, BRcommunity, corals, otherprocess, performance, review
Tropical coral reefs, a vital component of the global marine ecosystem, are currently under threat from climate change factors such as rising temperatures, ocean acidification, and extreme weather events. High temperatures induce coral bleaching, resulting in the loss of their energy supply and an acceleration of metabolic rates, rendering them more vulnerable. Ocean acidification affects the formation of calcium carbonate skeletons in symbiotic algae and decreases photosynthetic efficiency, further exacerbating the risk of damage to the symbiotic algae in high-temperature conditions. Extreme weather events directly cause physical damage to corals and alter marine environments, reducing their chances of survival. This review focuses on the impact of climate change on the biochemical adaptability between tropical hard corals and photosynthetic symbiotic algae, exploring their ecological relationship, the influence of climate change on this relationship, and the adaptive mechanisms. Understanding the adaptive mechanisms between hard corals and symbiotic algae is crucial for developing conservation strategies and management plans to maintain the functionality and biodiversity of coral reef ecosystems. It also aids in ensuring the survival and prosperity of this delicate relationship under the challenges posed by climate change, allowing future generations to continue enjoying the magnificence of tropical coral reefs.
Continue reading ‘Biochemical adaptability of the relationship between tropical hard corals and photosynthetic symbiotic algae under climate change ‘Inferring the health of coral reefs on the Egyptian coast of the Gulf of Aqaba for three branching-coral species
Published 9 January 2024 Science ClosedTags: biological response, chemistry, corals, field, growth, Red Sea
Abstract
This investigation examined the vulnerability of three branching coral species (Acropora humilis, Pocillopora damicornis, and Stylophora pistillata) to environmental changes within the marine reserves of Taba, Nuweiba, and Dahab in the Gulf of Aqaba. Coral growth rates were assessed as a key indicator of coral reef vitality, reacting to shifting physicochemical parameters. A. humilis manifested the highest growth rate, followed by S. pistillata and P. damicornis. Site-specific data analysis found Dahab displayed the greatest coral proliferation, with Taba exhibiting the least. Accounting for seasonal changes, spring showed maximal coral growth. Statistical analysis revealed a positive correlation between salinity and coral growth rate, contrasted by a negative correlation with variables such as pH, PO4-P, and silicate (SiO4-Si). This work underscores the significant influence of environmental factors on coral growth rates, and by extension, the health of coral reef ecosystems. These findings are integral to coral reef management, suggesting mitigation of adverse environmental factors could enhance these ecosystems’ resilience against climatic shifts and human-induced stressors. By combining species, site, seasonal, and physicochemical variations, this research underlines the importance of localized conservation strategies.
Highlights
- Robust Reef Health: The paper’s findings reveal a remarkable resilience and overall good health of coral reefs in Egypt’s protected marine environments, even when compared to reefs in more polluted and anthropogenically impacted areas.
- Effective Protection Measures: The study underscores the importance of the protective measures implemented in these marine preserves, indicating that they have played a crucial role in maintaining the health and status of the intricate and invaluable reef ecosystems.
- Catalyst for Further Research: The research outcomes provide a strong foundation for future studies aimed at identifying and implementing effective protective measures and adaptive management strategies for coral reefs in diverse ecosystems, with the goal of ensuring their long-term health and preservation.
- Highlighting Environmental Challenges: The paper emphasizes the relative health of the studied coral reefs despite broader environmental challenges, shedding light on the potential success of conservation efforts within these specific marine regions.
Shallow-water carbonate facies herald the onset of the Palaeocene eocene thermal maximum (Hazara basin, Northern Pakistan)
Published 27 December 2023 Science ClosedTags: abundance, biological response, community composition, corals, otherprocess, paleo, protists, sediment
Highlights
- Pre-PETM-onset neritic carbonates show early signs of what will occur during PETM.
- Corals declined over the study period, whereas foraminifera and red algae increased.
- Similar patterns can be observed in most of the Neotethys.
- Quantitative data are crucial to better understanding palaeo-environmental changes.
Abstract
We investigate the Palaeocene succession of the Hazara Basin (Northern Pakistan) to better understand the impact of climate change on marine carbonate-producing organisms. These shallow-water carbonates, deposited during the Late Palaeocene, before the onset of the Palaeocene-Eocene Thermal Maximum, were studied using a quantitative approach to highlight changes in the skeletal assemblage. We recognise a decrease in the abundance of colonial corals and green calcareous algae and an increase in larger benthic foraminifera and red calcareous algae from the early Thanetian to the late Thanetian. Increasing temperatures may represent a plausible cause for the decline of the more sensitive colonial corals in favor of the more tolerant larger benthic foraminifera. A similar pattern is observed in most successions deposited along the margins of the Neotethys Ocean, suggesting a connection with the Late Palaeocene environmental changes that heralded the PETM hyperthermal event. Our stratigraphic analysis of the Hazara Basin strata suggests that the biotic turnovers occurred during the Palaeocene – Eocene transition started already before the onset of the Palaeocene Eocene Thermal Maximum as recorded by the geochemical proxies.
Continue reading ‘Shallow-water carbonate facies herald the onset of the Palaeocene eocene thermal maximum (Hazara basin, Northern Pakistan)’Evaluating the effects of climate change and chemical, physical and biological stressors on nearshore coral reefs: a case study in the Great Barrier Reef, Australia
Published 15 December 2023 Science ClosedTags: biological response, communitymodeling, corals, modeling, South Pacific
An understanding of the combined effects of climate change and other anthropogenic stressors, such as chemical exposures, is essential for improving ecological risk assessments of vulnerable ecosystems. In the Great Barrier Reef, coral reefs are under increasingly severe duress from increasing ocean temperatures, acidification and cyclone intensities associated with climate change. In addition to these stressors, inshore reef systems, such as the Mackay Whitsunday coastal zone are being impacted by other anthropogenic stressors, including chemical, nutrient and sediment exposures related to more intense rainfall events that increase catchment runoff of contaminated waters. To illustrate an approach for incorporating climate change into ecological risk assessment frameworks, we developed an adverse outcome pathway network to conceptually delineate effects of climate variables and PSII herbicide (diuron) exposures on scleractinian corals. This informed the development of a Bayesian network to quantitatively compare the effects of historical (1975-2005) and future projected climate on inshore hard coral bleaching, mortality, and cover. This Bayesian network demonstrated how risk may be predicted for multiple physical and biological stressors including temperature, ocean acidification, cyclones, sediments, macroalgae competition, and crown of thorns starfish predation, as well as chemical stressors such as nitrogen and herbicides. Climate scenarios included an ensemble of 16 downscaled models encompassing current and future conditions based on multiple emission scenarios for two thirty-year periods. It was found that both climate-related and catchment-related stressors pose a risk to these inshore reef systems, with projected increases in coral bleaching and coral mortality under all future climate scenarios. This modelling exercise can support the identification of risk drivers for the prioritisation of management interventions to build future resilient reefs.
Continue reading ‘Evaluating the effects of climate change and chemical, physical and biological stressors on nearshore coral reefs: a case study in the Great Barrier Reef, Australia’Porites’ coral calcifying fluid chemistry regulation under normal- and low-pH seawater conditions in Palau Archipelago: impacts on growth properties
Published 28 November 2023 Science ClosedTags: biological response, calcification, corals, field, morphology, physiology, South Pacific
Highlights
- •Palau’s reef has a long-term naturally acidified inshore seawater (pH ~ 7.85).
- •Porites corals up-regulate calcifying fluid pH (~8.41) at normal- and low-pH sites.
- •Porites corals adapt calcifying fluid chemistry to long-term low-pH conditions.
- •Porites shows 15 % lower skeletal density under low-pH (~7.85) vs. open-ocean (~8.03).
Abstract
Ongoing ocean acidification is known to be a major threat to tropical coral reefs. To date, only few studies have evaluated the impacts of natural long-term exposure to low-pH seawater on the chemical regulation and growth of reef-building corals. This work investigated the different responses of the massive Porites coral living at normal (pHsw ~ 8.03) and naturally low-pH (pHsw ~ 7.85) seawater conditions at Palau over the last decades. Our results show that both Porites colonies maintained similar carbonate properties (pHcf, [CO32−]cf, DICcf, and Ωcf) within their calcifying fluid since 1972. However, the Porites skeleton of the more acidified conditions revealed a significantly lower density (~ 1.21 ± 0.09 g·cm−3) than the skeleton from the open-ocean site (~ 1.41 ± 0.07 g·cm−3). Overall, both Porites colonies exerted a strong biological control to maintain stable calcifying fluid carbonate chemistry that favored the calcification process, especially under low-pH conditions. However, the decline in skeletal density observed at low pH provides critical insights into Porites vulnerability to future global change.
Continue reading ‘Porites’ coral calcifying fluid chemistry regulation under normal- and low-pH seawater conditions in Palau Archipelago: impacts on growth properties’Editorial: the changing carbonate systems in coastal, estuarine, shelf areas and marginal seas
Published 23 November 2023 Science ClosedTags: Antarctic, Arctic, biogeochemistry, biological response, chemistry, corals, North Pacific, review
Editorial on the Research Topic
The changing carbonate systems in coastal, estuarine, shelf areas and marginal seas
Global atmospheric CO2 concentrations have increased from 320 ppm in the 1960s to the present-day value of 420 ppm, primarily due to anthropogenic activities. This increase influences the seawater carbonate system, impacting the marine ecosystem. There are still gaps that need to be resolved for predicting how these marine systems respond to current and future CO2 levels. Any actions to mitigate the change in pH will require adaptive management of multiple stressors across several spatial scales. Combined, these perspectives yield a more comprehensive picture of events during ocean acidification (OA).
This Research Topic brings together articles from different regions, including coastal, estuarine, and shelf areas and marginal seas, all susceptible to changing atmospheric conditions, riverine inputs, air-sea CO2 exchanges, and multiple acid-base reactions that can alter carbonate chemistry. Articles on the long-term trends of CO2 system descriptors and the interactions with calcifying organisms were also sought. The present Research Topic is primarily based on original articles devoted to carbonate systems in the marginal seas, but it is a pity that some interesting papers dealing with freshwater inflows, estuaries, and related coastal areas were not accepted.
Fransson et al. examined the effects of glacial and sea-ice meltwater on ocean acidification in the waters near the 79 North Glacier (79 NG) and the northeast Greenland shelf. The researchers investigated various ocean acidification factors and the influence of freshening, primary production, and air-sea CO2 exchange. One of the key findings was that the biological removal of CO2 through primary production played a crucial role in offsetting the negative impact of freshwater dilution on the aragonite saturation state (ΩAr), which is a measure of ocean acidification. This compensation effect was most pronounced in 2012, especially in the vicinity of the 79 NG front, where there was a significant presence of glacial meltwater and surface stratification. In 2016, a different scenario was observed, with a more homogenized water column due to sea-ice meltwater. In this case, the compensation effect of biological CO2 removal on ΩAr was weaker compared to 2012. The study also suggests that in the future, with ongoing climate and ocean chemistry changes, the increasing influence of meltwater may surpass the mitigating effects of biological CO2 removal. This could lead to unfavorable conditions for organisms that rely on calcium carbonate for their shells and skeletons. Thus, all the proposed factors need to be closely monitored as they could have significant implications for marine ecosystems and calcifying organisms in the face of ongoing environmental changes.
Continue reading ‘Editorial: the changing carbonate systems in coastal, estuarine, shelf areas and marginal seas’Short-term ocean acidification decreases pulsation and growth of the widespread soft coral Xenia umbellata
Published 20 November 2023 Science ClosedTags: abundance, biological response, corals, growth, laboratory, morphology, mortality, otherprocess, performance, photosynthesis, physiology, protists, respiration
Coral reefs may experience lower pH values as a result of ocean acidification (OA), which has negative consequences, particularly for calcifying organisms. Thus far, the effects of this global factor have been mainly investigated on hard corals, while the effects on soft corals remain relatively understudied. We therefore carried out a manipulative aquarium experiment for 21 days to study the response of the widespread pulsating soft coral Xenia umbellata to simulated OA conditions. We gradually decreased the pH from ambient (~8.3) to three consecutive 7-day long pH treatments of 8.0, 7.8, and 7.6, using a CO2 dosing system. Monitored response variables included pulsation rate, specific growth rate, visual coloration, survival, Symbiodiniaceae cell densities and chlorophyll a content, photosynthesis and respiration, and finally stable isotopes of carbon (C) and nitrogen (N) as well as CN content. Pulsation decreased compared to controls with each consecutive lowering of the pH, i.e., 17% at pH 8.0, 26% at pH 7.8 and 32% at pH 7.6, accompanied by an initial decrease in growth rates of ~60% at pH 8.0, not decreasing further at lower pH. An 8.3 ‰ decrease of δ13C confirmed that OA exposed colonies had a higher uptake and availability of atmospheric CO2. Coral productivity, i.e., photosynthesis, was not affected by higher dissolved inorganic C availability and none of the remaining response variables showed any significant differences. Our findings suggest that pulsation is a phenotypically plastic mechanism for X. umbellata to adjust to different pH values, resulting in reduced growth rates only, while maintaining high productivity. Consequently, pulsation may allow X. umbellata to inhabit a broad pH range with minimal effects on its overall health. This resilience may contribute to the competitive advantage that soft corals, particularly X. umbellata, have over hard corals.
Continue reading ‘Short-term ocean acidification decreases pulsation and growth of the widespread soft coral Xenia umbellata’Impact of ocean acidification on coral reefs and the marine ecosystems in Phillipines
Published 17 November 2023 Science ClosedTags: biological response, corals, policy, review, South Pacific
Purpose: The aim of the study was to investigate the impact of ocean acidification on coral reefs and the marine ecosystems in phillipines
Methodology: The study adopted a desktop methodology. Desk research refers to secondary data or that which can be collected without fieldwork. Desk research is basically involved in collecting data from existing resources hence it is often considered a low cost technique as compared to field research, as the main cost is involved in executive’s time, telephone charges and directories. Thus, the study relied on already published studies, reports and statistics. This secondary data was easily accessed through the online journals and library
Findings: Ocean acidification reduces the density and growth of coral skeletons, making them more vulnerable to erosion. This threatens coral reefs and the marine life that depends on them. It also affects human benefits from coral reefs, such as fisheries, tourism and storm protection.
Unique Contribution to Theory, Practice and Policy: Theory of Ocean Acidification and Coral Calcification, Theory of Ocean Acidification and Biodiversity Loss and Theory of Adaptation and Resilience of Coral Reefs may be used to anchor future studies on impact of ocean acidification on coral reefs and the marine ecosystems in Philippines. Philippine government should actively participate in global climate agreements and implement policies to reduce carbon emissions at the domestic level. The Philippine government should integrate ocean acidification considerations into national environmental policies and action plans, such as the Philippine Coral Reef Protection Program.
Continue reading ‘Impact of ocean acidification on coral reefs and the marine ecosystems in Phillipines’Complex dynamics of coral gene expression responses to low pH across species
Published 15 November 2023 Science ClosedTags: adaptation, biological response, BRcommunity, calcification, chemistry, community composition, corals, laboratory, molecular biology, morphology, mortality, North Atlantic, otherprocess, performance, physiology, protists
Coral capacity to tolerate low pH affects coral community composition and, ultimately, reef ecosystem function. Low pH submarine discharges (‘Ojo’; Yucatán, México) represent a natural laboratory to study plasticity and acclimatization to low pH in relation to ocean acidification. A previous >2-year coral transplant experiment to ambient and low pH common garden sites revealed differential survivorship across species and sites, providing a framework to compare mechanistic responses to differential pH exposures. Here, we examined gene expression responses of transplants of three species of reef-building corals (Porites astreoides, Porites porites and Siderastrea siderea) and their algal endosymbiont communities (Symbiodiniaceae) originating from low pH (Ojo) and ambient pH native origins (Lagoon or Reef). Transplant pH environment had the greatest effect on gene expression of Porites astreoides hosts and symbionts and P. porites hosts. Host P. astreoides Ojo natives transplanted to ambient pH showed a similar gene expression profile to Lagoon natives remaining in ambient pH, providing evidence of plasticity in response to ambient pH conditions. Although origin had a larger effect on host S. siderea gene expression due to differences in symbiont genera within Reef and Lagoon/Ojo natives, subtle effects of low pH on all origins demonstrated acclimatization potential. All corals responded to low pH by differentially expressing genes related to pH regulation, ion transport, calcification, cell adhesion and stress/immune response. This study demonstrates that the magnitude of coral gene expression responses to pH varies considerably among populations, species and holobionts, which could differentially affect acclimatization to and impacts of ocean acidification.
Continue reading ‘Complex dynamics of coral gene expression responses to low pH across species’Dive industry perspectives on threats to coral reefs: a comparative study across four Asia-Pacific countries
Published 15 November 2023 Science ClosedTags: corals, mitigation, North Pacific, policy, socio-economy, South Pacific
The combined effects of climate change, marine tourism and other stressors threaten the ecological and economic sustainability of coral reefs. This study investigates dive industry stakeholder awareness of the threats to coral reefs through structured interviews with Dive Masters, company managers and marine management agencies in Vietnam, Australia, Malaysia and Indonesia. Stakeholders from all locations have observed degradation of local reefs. Destructive fishing was identified as the principal threat in all regions except Australia. Most participants identified threats from climate change and marine tourism. There was a lack of awareness about ocean acidification by all participants from Maluku, Indonesia. However, ocean acidification could make coral more fragile and, therefore, vulnerable to diver-induced damage. The majority of Dive Masters across all regions provide pre-dive briefings to reduce diver impacts and participate in environmental activities to protect local reefs. Stakeholders in three regions thought there was capacity to expand the local dive industry. However, in Nha Trang Vietnam, most industry stakeholders thought they were at, or exceeded, carrying capacity, whereas marine management employees thought there was room to expand. This study highlights an opportunity to improve diver education on the vulnerability of coral to damage in acidifying oceans. This study also identifies various non-regulatory and regulatory strategies used to reduce diver impacts, emphasising the value of multi-national knowledge sharing between the dive industry and regulatory agencies for adaptive management.
HIGHLIGHTS
- Dive industry stakeholders are concerned about threats to coral reefs.
- Impacts from diving activities were recognised in three of four regions.
- There was great discrepancy between regions in the awareness of ocean acidification.
- Most dive industry stakeholders are engaged in marine conservation activities.
- Some marine managers and industry stakeholders had discrepant views on diver carrying capacity
Assessing the impact of ocean acidification on coral health and reef resilience
Published 10 November 2023 Science ClosedTags: biological response, corals, review
The potential effects of ocean acidification on marine ecosystems, especially coral reefs, have brought the topic to the forefront of environmental concerns. The purpose of this study is to evaluate how ocean acidification has affected coral wellness and reef resistance. The consequences of ocean acidification on coral physiology, growth, calcification, and symbiotic interactions are summarized in this article by reviewing the existing scientific literature and research results. The research also delves into what these repercussions mean for coral reefs’ overall resilience and considers possible mitigation techniques to lessen the blow ocean acidification deals to the ecosystem.
Continue reading ‘Assessing the impact of ocean acidification on coral health and reef resilience’Ocean warming and acidification detrimentally affect coral tissue regeneration at a Mediterranean CO2 vent
Published 19 October 2023 Science ClosedTags: biological response, corals, field, Mediterranean, physiology, vents
Highlights
- This is the first transplant experiment investigating coral tissue regeneration with decreasing pH and increasing temperature
- Increasing temperature and decreasing pH could detrimentally impact coral tissue regeneration following injury
- Zooxanthellate corals might be particularly impacted by ocean warming and acidification in terms of lesion recovery
Abstract
Among the main phenomena that are causing significant changes in ocean waters are warming and acidification, largely due to anthropogenic activities. Growing evidence suggests that climate change is having more substantial and rapid effects on marine communities than on terrestrial ones, triggering several physiological responses in these organisms, including in corals. Here we investigated, for first time in the field, the combined effect of increasing seawater acidification and warming on tissue regeneration rate of three Mediterranean scleractinian coral species characterized by different trophic strategies and growth modes. Balanophyllia europaea (solitary, zooxanthellate), Leptopsammia pruvoti (solitary, non-zooxanthellate) and Astroides calycularis (colonial, non-zooxanthellate) specimens were transplanted, during a cold, intermediate, and warm period, along a natural pH gradient generated by an underwater volcanic crater at Panarea Island (Mediterranean Sea, Italy), characterized by continuous and localized CO2 emissions at ambient temperature. Our results show a decrease in regenerative capacity, especially in the zooxanthellate species, with increasing seawater temperature and acidification, with demonstrated species-specific differences. This finding suggests that increasing seawater temperature and acidification could have a compounding effect on coral regeneration following injury, potentially hindering the capacity of corals to recover following physical disturbance under predicted climate change.
Continue reading ‘Ocean warming and acidification detrimentally affect coral tissue regeneration at a Mediterranean CO2 vent’Long-term coral microbial community acclimatization is associated with coral survival in a changing climate
Published 4 October 2023 Science ClosedTags: abundance, adaptation, biological response, BRcommunity, community composition, corals, laboratory, mesocosms, mortality, North Pacific, otherprocess, prokaryotes
The plasticity of some coral-associated microbial communities under stressors like warming and ocean acidification suggests the microbiome has a role in the acclimatization of corals to future ocean conditions. Here, we evaluated the acclimatization potential of coral-associated microbial communities of four Hawaiian coral species (Porites compressa, Porites lobata, Montipora capitata, and Pocillopora acuta) over 22-month mesocosm experiment. The corals were exposed to one of four treatments: control, ocean acidification, ocean warming, or combined future ocean conditions. Over the 22-month study, 33–67% of corals died or experienced a loss of most live tissue coverage in the ocean warming and future ocean treatments while only 0–10% died in the ocean acidification and control. Among the survivors, coral-associated microbial communities responded to the chronic future ocean treatment in one of two ways: (1) microbial communities differed between the control and future ocean treatment, suggesting the potential capacity for acclimatization, or (2) microbial communities did not significantly differ between the control and future ocean treatment. The first strategy was observed in both Porites species and was associated with higher survivorship compared to M. capitata and P. acuta which exhibited the second strategy. Interestingly, the microbial community responses to chronic stressors were independent of coral physiology. These findings indicate acclimatization of microbial communities may confer resilience in some species of corals to chronic warming associated with climate change. However, M. capitata genets that survived the future ocean treatment hosted significantly different microbial communities from those that died, suggesting the microbial communities of the survivors conferred some resilience. Thus, even among coral species with inflexible microbial communities, some individuals may already be tolerant to future ocean conditions. These findings suggest that coral-associated microbial communities could play an important role in the persistence of some corals and underlie climate change-driven shifts in coral community composition.
Continue reading ‘Long-term coral microbial community acclimatization is associated with coral survival in a changing climate’The synergistic negative effects of combined acidification and warming on the coral host and its symbiotic association with Symbiodiniaceae indicated by RNA-Seq differential expression analysis
Published 21 September 2023 Science ClosedTags: algae, biological response, corals, laboratory, molecular biology, multiple factors, North Pacific, temperature
Global warming and ocean acidification represent major threats to coral reefs, the combination of these stressors may have concomitant impacts on coral holobionts. However, the molecular mechanisms of the impacts and synergistic effects of acidification and warming on coral holobionts are rarely known, particularly from the point of coral-Symbiodiniaceae symbioses. In this study, using branching Acropora valida and massive Galaxea fascicularis as representatives in a laboratory system simulating acidification (pH 7.7) and/or warming (32 °C), the response of coral host, Symbiodiniaceae and their symbiotic association were investigated by high-throughput transcriptome sequencing (RNA-Seq) with pH 8.1 and 26 °C as controls. Based on differentially expressed genes (DEGs) analysis, acidification and/or warming show greater impacts on the gene expression of coral host than its symbiotic Symbiodiniaceae. Synergistic effects of combined acidification and warming are suggested by comparison with single stress, especially the synergistic negative effects on coral-Symbiodiniaceae symbioses are suggested, because the expression of most of the genes related to photosynthesis, nutrient metabolism and transfer, and the symbionts recognition are downregulated indicating the instability of the coral-Symbiodiniaceae symbioses. This study provides molecular evidence for the synergy of acidification and warming on coral holobionts. In particular, the synergistic negative effects on the nutrients and symbionts recognition-based coral-Symbiodiniaceae symbioses are highlighted, which is helpful for predicting the response of coral holobionts to future global climate changes.
Continue reading ‘The synergistic negative effects of combined acidification and warming on the coral host and its symbiotic association with Symbiodiniaceae indicated by RNA-Seq differential expression analysis’Elucidating the mechanisms of stress tolerance in reef-building coral holobionts
Published 21 September 2023 Science ClosedTags: abundance, algae, biological response, corals, growth, laboratory, molecular biology, mortality, multiple factors, otherprocess, photosynthesis, physiology, temperature
Coral reefs worldwide are threatened by climate change effects like increasing ocean warming and ocean acidification. These increased pressures cause a dysbiosis between the coral host, algal endosymbionts, and associated coral microbiome that results in the coral host expelling algal endosymbionts, leaving the coral host with a stark white ‘bleached’ appearance. Without their endosymbionts, coral hosts are forced to sustain themselves energetically with heterotrophy instead of relying on the autotrophic carbon and energy sources that once came from the algal endosymbionts. When this response, termed ‘coral bleaching’, happens reef-wide during an extreme wave of increased ocean temperatures, this is called a mass Coral Bleaching Event. The frequency and intensity of mass Coral Bleaching events are increasing around the world, forcing corals to acclimatize to survive. This dissertation investigates the physiological and genomic mechanisms underlying acclimatization and increased stress tolerance in two common, reef-building corals: Montipora capitata and Pocillopora acuta. In three chapters, I present findings that support phenotypic plasticity and increased stress tolerance in M. capitata and hypothesize the mechanisms contributing to this. In Chapter 1, I conducted an ex-situ experiment that mimicked an environmentally realistic, extended heatwave and ocean acidification scenario in a factorial design of increased temperature and increased pCO2 conditions for a two-month stress period and a two-month recovery period. Both species’ physiological states were significantly challenged but M. capitata displayed a more favorable photosynthetic rate to antioxidant capacity ratio and associated with more thermally tolerant symbionts. Although M. capitata survived at higher rates than P. acuta, physiological state was still significantly impacted after two months of recovery, suggesting that marine heatwaves likely induce physiological legacies that may impact performance during the next, inevitable heatwave. In Chapter 2, I further investigated P. acuta’s stress response from Chapter 1 at a genomic level. We sought to test the effects of environmental stressors on gene body DNA methylation patterns to elucidate how environmentally sensitive and dynamic DNA methylation changes are in invertebrates. However, when analyzing gene expression data, our team found that polyploidy was prevalent in our samples, which convoluted our ability to test environmental effect in addition to polyploidy structure. We found that DNA methylation patterns followed polyploidy genetic lineage with diploid corals exhibiting the highest levels of DNA methylation despite lower gene expression levels of epigenetic machinery proteins. Despite significant DNA methylation pattern differences between polyploidies, P. acuta populations still severely declined in increased stress conditions (outlined in Chapter 1), suggesting that regardless of differential gene body methylation and ploidy status, this species may be ultimately too sensitive to future ocean conditions. In Chapter 3, I further investigated the genomic mechanisms underlying stress response in Montipora capitata, by directly comparing bleached (‘Susceptible’) and non-bleached (‘Resistant’) phenotypes of conspecific pairs. We found very little genetic diversity among our samples suggesting there is no effect of genetic structure on phenotypic variation in this context. ‘Resistant’ corals were characterized by association with more thermally tolerant symbionts, lower gene expression variability, higher gene body methylation levels on genes involved in death and stress response, and a more robust cellular stress response. The results of all three chapters suggest that both physiological and genomic stats impact bleaching susceptibility and phenotype and that not one mechanism may act alone to produce a particular phenotype. This dissertation aids in elucidating the mechanisms of stress response in reef-building corals, ultimately guiding our current knowledge of phenotypic variation in the face of climate change.
Continue reading ‘Elucidating the mechanisms of stress tolerance in reef-building coral holobionts’Long-term preconditioning of the coral Pocillopora acuta does not restore performance in future ocean conditions
Published 28 August 2023 Science ClosedTags: abundance, algae, biological response, corals, laboratory, multiple factors, otherprocess, photosynthesis, physiology, South Pacific, temperature
There is overwhelming evidence that tropical coral reefs are severely impacted by human induced climate change. Assessing the capability of reef-building corals to expand their tolerance limits to survive projected climate trajectories is critical for their protection and management. Acclimation mechanisms such as developmental plasticity may provide one means by which corals could cope with projected ocean warming and acidification. To assess the potential of preconditioning to enhance thermal tolerance in the coral Pocillopora acuta, colonies were kept under three different scenarios from settlement to 17 months old: present day (0.9 °C-weeks (Degree Heating Weeks), + 0.75 °C annual, 400 ppm pCO2) mid-century (2.5 °C-weeks, + 1.5 °C annual, 685 ppm pCO2) and end of century (5 °C-weeks, + 2 °C annual, 900 ppm pCO2) conditions. Colonies from the present-day scenario were subsequently introduced to the mid-century and end of century conditions for six weeks during summer thermal maxima to examine if preconditioned colonies (reared under these elevated conditions) had a higher physiological performance compared to naive individuals. Symbiodiniaceae density and chlorophyll a concentrations were significantly lower in mid-century and end of century preconditioned groups, and declines in symbiont density were observed over the six-week accumulated heat stress in all treatments. Maximum photosynthetic rate was significantly suppressed in mid-century and end of century preconditioned groups, while minimum saturating irradiances were highest for 2050 pre-exposed individuals with parents originating from specific populations. The results of this study indicate preconditioning to elevated temperature and pCO2 for 17 months did not enhance the physiological performance in P. acuta. However, variations in trait responses and effects on tolerance found among treatment groups provides evidence for differential capacity for phenotypic plasticity among populations which could have valuable applications for future restoration efforts.
Continue reading ‘Long-term preconditioning of the coral Pocillopora acuta does not restore performance in future ocean conditions’Brown seaweed Nemacystus decipiens intensifies the effects of ocean acidification on coral Montipora digitata
Published 22 August 2023 Science ClosedTags: algae, biological response, calcification, communityMF, corals, laboratory, multiple factors, North Pacific, photosynthesis
Photosynthetic marine macrophytes such as seaweeds have been proposed to provide habitat refugia for marine calcifiers against ocean acidification (OA) by increasing the local pH. However, the effectiveness of seaweed as a potential habitat refugia for marine calcifiers such as corals remains to be investigated. This study focused on the seaweed Nemacystus decipiens, which are widely farmed in the shallow reef lagoon of Okinawa coral reefs, Japan, and aimed to evaluate their response to high pCO2 and whether they can mitigate the effect of high pCO2 on the coral Montipora digitata. Corals were cultured with and without seaweed under control (300–400 μatm) or high pCO2 conditions (OA, 900–1000 μatm) for 2 weeks. Results showed that all photo-physiological parameters examined in the seaweed N. decipiens were not affected by high pCO2, suggesting that OA will not positively affect their productivity. The calcification rate of the coral M. digitata was found to decrease under OA and the effect was further exaggerated by the presence of seaweed. The present study suggests that farming seaweeds will not act as a potential habitat refugia for adjacent corals under future OA, but instead can exaggerate the negative effect of OA on coral calcification.
Continue reading ‘Brown seaweed Nemacystus decipiens intensifies the effects of ocean acidification on coral Montipora digitata’
