Ocean acidification, caused by anthropogenic CO2 emissions, is predicted to have major consequences for reef-building corals, jeopardizing the scaffolding of the most biodiverse marine habitats. However, whether corals can adapt to ocean acidification and how remains unclear. We addressed these questions by re-examining transcriptome and genome data of Acropora millepora coral holobionts from volcanic CO2 seeps with end-of-century pH levels. We show that adaptation to ocean acidification is a wholistic process involving the three main compartments of the coral holobiont. We identified 441 coral host candidate adaptive genes involved in calcification, response to acidification, and symbiosis; population genetic differentiation in dinoflagellate photosymbionts; and consistent transcriptional microbiome activity despite microbial community shifts. Coral holobionts from natural analogues to future ocean conditions harbor beneficial genetic variants with far-reaching rapid adaptation potential. In the face of climate change, these populations require immediate conservation strategies as they could become key to coral reef survival.
Continue reading ‘Genomic signatures suggesting adaptation to ocean acidification in a coral holobiont from volcanic CO2 seeps’Posts Tagged 'vents'
Genomic signatures suggesting adaptation to ocean acidification in a coral holobiont from volcanic CO2 seeps
Published 25 July 2023 Science ClosedTags: adaptation, biological response, BRcommunity, corals, field, molecular biology, otherprocess, physiology, phytoplankton, prokaryotes, South Pacific, vents
Brain transcriptome of gobies inhabiting natural CO2 seeps reveal acclimation strategies to long-term acidification
Published 11 July 2023 Science ClosedTags: adaptation, biological response, field, fish, Mediterranean, molecular biology, otherprocess, vents
Ocean acidification (OA) is known to affect the physiology, survival, behaviour and fitness of various fish species with repercussions at the population, community and ecosystem levels. Some fish species, however, seem to acclimate rapidly to OA conditions and even thrive in acidified environments. The molecular mechanisms that enable species to successfully inhabit high CO2 environments have not been fully elucidated especially in wild fish populations. Here, we used the natural CO2 seep in Vulcano Island, Italy to study the effects of elevated CO2 exposure on the brain transcriptome of the anemone goby, a species with high population density in the CO2 seep and investigate their potential for acclimation. Compared to fish from environments with ambient CO2, gobies living in the CO2 seep showed differences in the expression of transcripts involved in ion transport and pH homeostasis, cellular stress, immune response, circadian rhythm and metabolism. We also found evidence of potential adaptive mechanisms to restore the functioning of GABAergic pathways, whose activity can be affected by exposure to elevated CO2 levels. Our findings indicate that gobies living in the CO2 seep may be capable of mitigating CO2-induced oxidative stress and maintaining physiological pH while meeting the consequent increased energetic costs. The conspicuous difference in the expression of core circadian rhythm transcripts could provide an adaptive advantage by increasing the flexibility of physiological processes in elevated CO2 conditions thereby facilitating acclimation. Our results show potential molecular processes of acclimation to elevated CO2 in gobies enabling them to thrive in the acidified waters of Vulcano Island.
Continue reading ‘Brain transcriptome of gobies inhabiting natural CO2 seeps reveal acclimation strategies to long-term acidification’Microbial dynamics in shallow CO2 seeps system off Panarea Island (Italy)
Published 30 June 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, field, Mediterranean, otherprocess, physiology, prokaryotes, vents
Shallow-water hydrothermal vents are extreme environments characterized by high temperatures, low pH, and high CO2 concentrations; therefore, they are considered as suitable laboratories for studying the effect of global changes on marine microbes. We hypothesized a direct effect of vents on prokaryotic community structure and functioning in the Panarea Island’s hydrothermal system. Sampling was conducted along a 9-station transect characterized by three active emission points. The water column was stratified with a thermocline at 25 m depth and a deep chlorophyll maximum between 50 and 100 m. Prokaryotic abundance ranged from 0.2 to 1.5 × 109 cells L−1, prokaryotic carbon production from 2.4 to 75.4 ng C L−1 h−1, and exoenzymatic activities degrading proteins, phosphorylated compounds, and polysaccharides were on the order of 4–28, 2–31 and 0.2–4.16 nM h−1, respectively. While microbial abundance and production were shaped by the water column’s physical structure, alkaline phosphatase and beta-glucosidase activities seemed to be enhanced by hydrothermal fluids. The 16S rRNA gene amplicon sequencing analysis identified a surface, a deep, and a vent-influenced microbial community. In terms of relative abundance members of the SAR11 group dominated the water column, alongside Synechococcus and Prochlorococcus in surface and bottom samples, respectively. Vent-influenced stations were characterized by the presence of Thiomicrorhabdus, a sulfur-oxidizer chemolithoautotroph. Overall, this study provides insights on the coupling between microbial community structure and the biogeochemical cycling of nutrients in low-pH conditions (CO2 and H2S-based), thus addressing some of the opened questions about the response of microbes to acidification.
Continue reading ‘Microbial dynamics in shallow CO2 seeps system off Panarea Island (Italy)’Alvania acida sp. nov., a new late Quaternary gastropod adapted to the shallow-marine CO2 seep of Vulcano Island
Published 19 June 2023 Science ClosedTags: biological response, field, Mediterranean, mollusks, morphology, vents
Submarine CO2 emissions are a recent (probably younger than about 5 ka) expression of volcanism at Vulcano Island (off NE Sicily), a Mediterranean natural laboratory for the study of ocean acidification. An impoverished molluskan association is known from the naturally acidified waters of Vulcano, at Levante Bay, where pH drops to 5.64. Here we describe a new gastropod, Alvania acida sp. nov., living in the bay, and found at the nearby site of Capo Milazzo (NE coast of Sicily) within a Late Pleistocene paleocommunity related to vegetated bottoms. The study species underwent a habitat change during its short evolutionary history, resulting in the recent adaptation to the CO2 seep at Vulcano. Similarly to the gastropods Tritia corniculum and T. neritea from the same seep, A. acida was up to 24% smaller than fossil shells from Milazzo, showing a further probable case of adaptation to high-CO2 waters through dwarfing. The new species shows distinctive features: an inflated shell; very convex, axially ribbed whorls; weak spiral cords. Because of its current distribution, limited to Levante Bay, and anthropogenic pressure from tourism affecting the site, A. acida deserves protection.
Continue reading ‘Alvania acida sp. nov., a new late Quaternary gastropod adapted to the shallow-marine CO2 seep of Vulcano Island’Direct H2S, HS− and pH measurements of high-temperature hydrothermal vent fluids with in situ Raman spectroscopy
Published 31 May 2023 Science ClosedTags: chemistry, field, methods, North Pacific, vents
Abstract
Hydrothermal H2S is an important energy source for hydrothermal ecosystems. However, it is difficult to obtain accurate hydrogen sulfide concentrations in high-temperature hydrothermal fluids because they are highly susceptible to oxidation and compositional variability with mixing. In this study, a new in situ approach for measuring H2S, HS− and pH in hydrothermal fluids was developed and applied to the detections of Okinawa Trough hydrothermal activities. The in situ total H2S concentrations in the Jade and Biwako fluids were determined to be 31.4 and 76.7 mmol/kg, respectively. The in situ measured pH of the Jade fluids was determined to be 6.3, which has exceeded that of a neutral fluid at a specific temperature and pressure, indicating that the pH of Jade fluids is weakly alkaline. The pH transition of hydrothermal fluids from alkaline to acidic may be attributed to the thermal decomposition of organic matter and sulfide precipitation.
Key Points
- The first in situ measured pH of high-temperature hydrothermal vent fluids at arc-back arc basins was reported
- A new approach to obtain in situ H2S/HS− concentration and in situ pH of high temperature hydrothermal vent fluids was established
- The pH transition of hydrothermal fluids from alkaline to acidic should attributes to the precipitation of sulfide minerals
Abundance and size structure of Patella spp. (Mollusca, Gastropoda) under ocean acidification conditions at CO2 vents (Ischia Island, Italy)
Published 25 April 2023 Science ClosedTags: abundance, biological response, dissolution, field, Mediterranean, mollusks, morphology, otherprocess, vents
Abundance and size structure of Patella spp. were studied at Ischia Island (Tyrrhenian Sea) in two populations living at CO2 vents off Castello Aragonese, under natural ocean acidification (OA) conditions (pH 7.4-7.9), and three control populations in sites characterized by normal pH conditions (pH 8.1). Both CO2 vent populations had 95% of heavily corroded shells and significant lower abundances than control populations, while the size structure showed individuals of higher dimensions (>2 cm), fewer small specimens (0-1 cm) and lack of new recruits in the vent’s populations subjected to OA conditions. These results confirm that, although with low densities, limpets thrive under OA conditions, and exhibit larger sizes, than in control areas, but a reduced recruitment of juveniles. This fact suggests a habitat selection only by adult specimens likely more robust to OA then juveniles, and the potential influence of other indirect factors, such as the amount and quality of the plant food (higher N content), which seems higher under OA conditions, or a reduced predation, that can explain the larger limpet’s size.
Continue reading ‘Abundance and size structure of Patella spp. (Mollusca, Gastropoda) under ocean acidification conditions at CO2 vents (Ischia Island, Italy)’High abundances of zooxanthellate zoantharians (Palythoa and Zoanthus) at multiple natural analogues: potential model anthozoans?
Published 21 April 2023 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, cnidaria, community composition, field, North Pacific, otherprocess, South Pacific, vents
Whilst natural analogues for future ocean conditions such as CO2 seeps and enclosed lagoons in coral reef regions have received much recent research attention, most efforts in such locations have focused on the effects of prolonged high CO2 levels on scleractinian corals and fishes. Here, we demonstrate that the three species of zooxanthellate zoantharians, hexacorallian non-calcifying “cousins” of scleractinians, are common across five coral reef natural analogue sites with high CO2 levels in the western Pacific Ocean, in Japan (n = 2), Palau, Papua New Guinea, and New Caledonia (n = 1 each). These current observations support previously reported cases of high Palythoa and Zoanthus abundance and dominance on various impacted coral reefs worldwide. The results demonstrate the need for more research on the ecological roles of zooxanthellate zoantharians in coral reef systems, as well as examining other “understudied” taxa that may become increasingly important in the near future under climate change scenarios. Given their abundance in these sites combined with ease in sampling and non-CITES status, some zoantharian species should make excellent hexacoral models for examining potential resilience or resistance mechanisms of anthozoans to future high pCO2 conditions.
Continue reading ‘High abundances of zooxanthellate zoantharians (Palythoa and Zoanthus) at multiple natural analogues: potential model anthozoans?’Volcanic-associated ecosystems of the Mediterranean Sea: a systematic map and an interactive tool to support their conservation
Published 11 April 2023 Science ClosedTags: biological response, BRcommunity, field, Mediterranean, methods, review, vents
Background
Hydrothermal vents, cold seeps, pockmarks and seamounts are widely distributed on the ocean floor. Over the last fifty years, the knowledge about these volcanic-associated marine ecosystems has notably increased, yet available information is still limited, scattered, and unsuitable to support decision-making processes for the conservation and management of the marine environment.
Methods
Here we searched the Scopus database and the platform Web of Science to collect the scientific information available for these ecosystems in the Mediterranean Sea. The collected literature and the bio-geographic and population variables extracted are provided into a systematic map as an online tool that includes an updated database searchable through a user-friendly R-shiny app.
Results
The 433 literature items with almost one thousand observations provided evidence of more than 100 different volcanic-associated marine ecosystem sites, mostly distributed in the shallow waters of the Mediterranean Sea. Less than 30% of these sites are currently included in protected or regulated areas. The updated database available in the R-shiny app is a tool that could guide the implementation of more effective protection measures for volcanic-associated marine ecosystems in the Mediterranean Sea within existing management instruments under the EU Habitats Directive. Moreover, the information provided in this study could aid policymakers in defining the priorities for the future protection measures needed to achieve the targets of the UN Agenda 2030.
Continue reading ‘Volcanic-associated ecosystems of the Mediterranean Sea: a systematic map and an interactive tool to support their conservation’High taxonomic diversity and miniaturization in benthic communities under persistent natural CO2 disturbances
Published 7 April 2023 Science ClosedTags: biological response, BRcommunity, community composition, field, methods, molecular biology, North Atlantic, otherprocess, vents
Metabarcoding techniques have revolutionized ecological research in recent years, facilitating the differentiation of cryptic species and revealing previously hidden diversity. In the current scenario of climate change and ocean acidification, biodiversity loss is one of the main threats to marine ecosystems. Here, we explored the effects of ocean acidification on marine benthic communities using DNA metabarcoding to assess the diversity of algae and metazoans. Specifically, we examined the natural pH gradient generated by the Fuencaliente CO2 vent system, located near La Palma Island (Canary Islands). High-resolution COI metabarcoding analyses revealed high levels of taxonomic diversity in an acidified natural area for the first time. This high number of species arises from the detection of small and cryptic species that were previously undetectable by other techniques. Such species are apparently tolerant to the acidification levels expected in future oceans. Hence and following our results, future subtropical communities are expected to keep high biodiversity values under an acidification scenario, although they will tend toward overall miniaturization due to the dominance of small algal and invertebrate species, leading to changes in ecosystem functions.
Footnotes
Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.6461937.
Continue reading ‘High taxonomic diversity and miniaturization in benthic communities under persistent natural CO2 disturbances’Field development of Posidonia oceanica seedlings changes under predicted acidification conditions
Published 27 March 2023 Science ClosedTags: biological response, laboratory, Mediterranean, morphology, phanerogams, physiology, reproduction, vents
Ocean acidification has been consistently evidenced to have profound and lasting impacts on marine species. Observations have shown seagrasses to be highly susceptible to future increased pCO2 conditions, but the responses of early life stages as seedlings are poorly understood. This study aimed at evaluating how projected Mediterranean Sea acidification affects the survival, morphological and biochemical development of Posidonia oceanica seedlings through a long-term field experiment along a natural low pH gradient. Future ocean conditions seem to constrain the morphological development of seedlings. However, high pCO2 exposures caused an initial increase in the degree of saturation of fatty acids in leaves and then improved the fatty acid adjustment increasing unsaturation levels in leaves (but not in seeds), suggesting a nutritional compound translocation. Results also suggested a P. oceanica structural components remodelling which may counteract the effects of ocean acidification but would not enhance seagrass seedling productivity.
Continue reading ‘Field development of Posidonia oceanica seedlings changes under predicted acidification conditions’Ocean acidification stunts molluscan growth at CO2 seeps
Published 15 March 2023 Science ClosedTags: biological response, field, mollusks, morphology, North Pacific, physiology, vents
Highlights
- Responses of molluscan growth to ocean acidification at CO2 seeps were studied.
- Mussels near CO2 seeps grew significantly slower than those outside the seeps.
- Mussels near and outside CO2 seeps exhibited differences in tissue carbon and nitrogen isotopic signatures.
- Geochemical analysis indicated chemical shifts at the calcifying front in mussels near and outside CO2 seeps.
Abstract
Ocean acidification can severely affect bivalve molluscs, especially their shell calcification. Assessing the fate of this vulnerable group in a rapidly acidifying ocean is therefore a pressing challenge. Volcanic CO2 seeps are natural analogues of future ocean conditions that offer unique insights into the scope of marine bivalves to cope with acidification. Here, we used a 2-month reciprocal transplantation of the coastal mussel Septifer bilocularis collected from reference and elevated pCO2 habitats to explore how they calcify and grow at CO2 seeps on the Pacific coast of Japan. We found significant decreases in condition index (an indication of tissue energy reserves) and shell growth of mussels living under elevated pCO2 conditions. These negative responses in their physiological performance under acidified conditions were closely associated with changes in their food sources (shown by changes to the soft tissue δ13C and δ15N ratios) and changes in their calcifying fluid carbonate chemistry (based on shell carbonate isotopic and elemental signatures). The reduced shell growth rate during the transplantation experiment was further supported by shell δ13C records along their incremental growth layers, as well as their smaller shell size despite being of comparable ontogenetic ages (5–7 years old, based on shell δ18O records). Taken together, these findings demonstrate how ocean acidification at CO2 seeps affects mussel growth and reveal that lowered shell growth helps them survive stressful conditions.
Continue reading ‘Ocean acidification stunts molluscan growth at CO2 seeps’Thanks mum. Maternal effects in response to ocean acidification of sea urchin larvae at different ecologically relevant temperatures
Published 3 March 2023 Science ClosedTags: biological response, echinoderms, Mediterranean, morphology, multiple factors, reproduction, temperature, vents
Highlights
- Ocean acidification and temperature differently influence larval development of Arbacia lixula and Paracentrotus lividus.
- Larvae of the two A. lixula populations (ambient-pH vs vent sites) respond differently to ocean acidification and temperature.
- Maternal buffer effect was observed in response to ocean acidification and temperature in both species.
- A. lixula seems to be more tolerant to changes in temperature than P. lividus.
Abstract
Juvenile stages of marine species might be more vulnerable than adults to climate change, however larval vulnerability to predictable environmental changes can be mitigated by parental anticipatory buffer effects occurring during gametogenesis. In this study, ocean acidification effect were investigated on larval growth of two sea urchins, Arbacia lixula and Paracentrotus lividus, at different temperature levels. Results showed that altered pH and temperature affected larval development in both species, with significant length reductions of spicules and significant increases in abnormal larvae. Detrimental effects of reduced pH and high temperature were however dependent on the mother. Furthermore, the responses of A. lixula larvae from the ambient site (pH ∼ 8.0) were compared with those of larvae obtained from mothers collected from a natural CO2 vent (pH ∼ 7.7) in Ischia. Comparisons highlighted a transgenerational response, as the CO2 vent larvae proved to be more resilient to reduced pH, although more sensitive to increased temperature.
Continue reading ‘Thanks mum. Maternal effects in response to ocean acidification of sea urchin larvae at different ecologically relevant temperatures’Acclimatization of a coral-dinoflagellate mutualism at a CO2 vent
Published 14 February 2023 Science ClosedTags: abundance, biological response, corals, field, Mediterranean, molecular biology, otherprocess, photosynthesis, phytoplankton, vents
Ocean acidification caused by shifts in ocean carbonate chemistry resulting from increased atmospheric CO2 concentrations is threatening many calcifying organisms, including corals. Here we assessed autotrophy vs heterotrophy shifts in the Mediterranean zooxanthellate scleractinian coral Balanophyllia europaea acclimatized to low pH/high pCO2 conditions at a CO2 vent off Panarea Island (Italy). Dinoflagellate endosymbiont densities were higher at lowest pH Sites where changes in the distribution of distinct haplotypes of a host-specific symbiont species, Philozoon balanophyllum, were observed. An increase in symbiont C/N ratios was observed at low pH, likely as a result of increased C fixation by higher symbiont cell densities. δ13C values of the symbionts and host tissue reached similar values at the lowest pH Site, suggesting an increased influence of autotrophy with increasing acidification. Host tissue δ15N values of 0‰ strongly suggest that diazotroph N2 fixation is occurring within the coral tissue/mucus at the low pH Sites, likely explaining the decrease in host tissue C/N ratios with acidification. Overall, our findings show an acclimatization of this coral-dinoflagellate mutualism through trophic adjustment and symbiont haplotype differences with increasing acidification, highlighting that some corals are capable of acclimatizing to ocean acidification predicted under end-of-century scenarios.
Continue reading ‘Acclimatization of a coral-dinoflagellate mutualism at a CO2 vent’Investigation of the molecular mechanisms which contribute to the survival of the polychaete Platynereis spp. under ocean acidification conditions in the CO2 vent system of Ischia Island (Italy)
Published 9 February 2023 Science ClosedTags: biological response, field, molecular biology, physiology, vents, zooplankton
The continuous increase of CO2 emissions in the atmosphere due to anthropogenic activities is one of the most important factors that contribute to Climate Change and generates the phenomenon known as Ocean Acidification (OA). Research conducted at the CO2 vents of Castello Aragonese (Ischia, Italy), which represents a natural laboratory for the study of OA, demonstrated that some organisms, such as polychaetes, thrive under acidified conditions through different adaptation mechanisms. Some functional and ecological traits promoting tolerance to acidification in these organisms have been identified, while the molecular and physiological mechanisms underlying acclimatisation or genetic adaptation are still largely unknown. Therefore, in this study we investigated epigenetic traits, as histone acetylation and methylation, in Platynereis spp. individuals coming from the Castello vent, and from a nearby control site, in two different periods of the year (November-June). Untargeted metabolomics analysis was also carried out in specimens from the two sites. We found a different profile of acetylation of H2B histone in the control site compared to the vent as a function of the sampling period. Metabolomic analysis showed clear separation in the pattern of metabolites in polychaetes from the control site with respect to those from the Castello vent. Specifically, a significant reduction of lipid/sterols and nucleosides was measured in polychaetes from the vent. Overall results contribute to better understand the potential metabolic pathways involved in the tolerance to OA.
Continue reading ‘Investigation of the molecular mechanisms which contribute to the survival of the polychaete Platynereis spp. under ocean acidification conditions in the CO2 vent system of Ischia Island (Italy)’Can marine hydrothermal vents be used as natural laboratories to study global change effects on zooplankton in a future ocean?
Published 23 January 2023 Science ClosedTags: biological response, methods, review, vents, zooplankton
It is claimed that oceanic hydrothermal vents (HVs), particularly the shallow water ones, offer particular advantages to better understand the effects of future climate and other global change on oceanic biota. Marine hydrothermal vents (HVs) are extreme oceanic environments that are similar to projected climate changes of the earth system ocean (e.g., changes of circulation patterns, elevated temperature, low pH, increased turbidity, increased bioavailability of toxic compounds. Studies on hydrothermal vent organisms may fill knowledge gaps of environmental and evolutionary adaptations to this extreme oceanic environment. In the present contribution we evaluate whether hydrothermal vents can be used as natural laboratories for a better understanding of zooplankton ecology under a global change scenario.
Continue reading ‘Can marine hydrothermal vents be used as natural laboratories to study global change effects on zooplankton in a future ocean?’Posidonia bonsai: dwarf Posidonia oceanica shoots associated to hydrothemal vent systems (Panarea Island, Italy)
Published 11 January 2023 Science ClosedTags: biological response, field, Mediterranean, morphology, phanerogams, vents
Highlights
- Dwarf Posidonia oceanica (bonsai) observed in hydrothermal vents off Panarea.
- Bonsai shoots are from 61–75% smaller in leaf biomass than regular-sized shoots
- Bonsai shoots lacks the regular seasonal pattern in sheath thickness (lepidochronology) of normal-sized shoots
Abstract
Very small-sized shoots of the Mediterranean seagrass Posidonia oceanica, defined as “bonsai” shoots, were found in areas with most intense CO2 emissions and low pH associated with four vents systems off Panarea island (Aeolian Archipelago, Sicily, Southern Tyrrhenian Sea). Bonsai shoots were sampled in September 2021 and October 2022: Bottaro crater (8 m depth), Camp 7 (16 m and 21 m), Black Point (20 m) and Hot/Cold Points (10 m). They had 2–6 leaves, and adult-intermediate leaves were 5–21 cm long and 3.5–7 mm wide, with leaf shoot surface ranging 4.8 and 44.5 cm2, and shoot leaf biomass between 16 and 89 mg (d.w.). These values were all significantly lower (t-test p < 0.006–0.0001) than those measured in normal-sized shoots collected within the vents and in control sites not affected by gas emissions. Bonsai shoots had 86–89% lower leaf surface, and 61–75% lower leaf biomass than all normal-sized shoots measured. The sheath thickness of the bonsai shoots was very low (0.1–0.8 mm), and the temporal trend of sheath thickness along the rhizome (lepidochronology) showed an irregular pattern, without the clear cyclical seasonal variation typical of normal-sized shoots. The reasons of size reduction and lack of temporal cycle in lepidochronology are discussed in the light of plant acclimatization and the constraints imposed by the continuous exposure to the stressful conditions of seawater acidification and presence of phytotoxic gases (e.g. hydrogen sulfide) in the vents.
Continue reading ‘Posidonia bonsai: dwarf Posidonia oceanica shoots associated to hydrothemal vent systems (Panarea Island, Italy)’Responses of corals and coral reef ecosystems to ocean acidification under variable temperature and light
Published 19 December 2022 Science ClosedTags: biological response, BRcommunity, calcification, corals, field, growth, laboratory, light, molecular biology, mortality, multiple factors, photosynthesis, physiology, protists, temperature, vents
Coral reefs are under increasing pressure from ocean acidification. However, much of our understanding is based on single-species aquarium experiments made in isolation from realistic environmental parameters (e.g. light, water flow, food supply) and other co occurring stressors (e.g. increasing sea surface temperatures, reduced water clarity due to terrestrial runoff). In my PhD project I aimed to understand how ocean acidification affects the ecophysiology of reef corals and reef communities in natural settings, and how effects may differ with concurrent exposure to variable temperature and light. I used a combination of experimental and observational studies at unique field sites with naturally high levels of CO2 (CO2 seep sites), and multi-factor experiments in the aquarium facilities of The Australian Institute of Marine Science’s National Sea Simulator to address these questions.
In chapter 2, I investigated if corals can acclimate to ocean acidification by switching their photosymbionts to types that may be able to utilise the more abundant CO2 in photosynthesis. I used molecular techniques to investigate the dominant photosymbiont types in six species of coral from the field and found them to be highly conserved within species between CO2 seep and control sites. In chapter 3, I used a combination of field surveys and a multifactor laboratory experiment to investigate if elevated CO2 increased the severity of coral thermal bleaching. Field surveys during a bleaching event at the CO2 seeps, as well as the experimental study, both showed that corals were not significantly more susceptible to thermal stress under high CO2. In chapter 4, I used a multifactor laboratory experiment to investigate if reduced or variable daily light availability affected the responses of corals to high CO2. Here I found that reductions in light levels, regardless of the variability in daily light integrals, can reduce coral growth rates more than high CO2. In chapter 5, I followed the development of early successional coral reef benthic communities on settlement tiles along a gradient of CO2 exposure at the seep sites, and further measured rates of community metabolism. Here high CO2 strongly influenced the development of communities, shifting them away from a dominance of calcifying taxa under present day conditions to a range of non-calcifying algae as CO2 levels increased. These high CO2 communities progressively recorded lower rates of calcification and higher rates of hotosynthesis at high CO2.
Results from this thesis show that the considerable changes to the CO2 seep benthic communities are likely due to secondary ecological effects, rather than the physiological effects on corals alone. Moreover, the negative effects of cooccurring stressors on corals and coral reefs will also be substantial. Hence there is an immediate need to reduce atmospheric CO2 emissions and improve the management of local stressors to prevent further declines to the health and functioning of coral reef ecosystems.
Continue reading ‘Responses of corals and coral reef ecosystems to ocean acidification under variable temperature and light’Characteristics of calcium isotopes at different water depths and their palaeoenvironmental significance for carbonate rocks of the Permian-Triassic boundary in Chibi, southern China
Published 24 November 2022 Science ClosedTags: biogeochemistry, field, North Pacific, paleo, vents
Calcium isotopes of carbonate rocks can trace calcium cycles and record changes in the marine environment. As published calcium isotope profiles of carbonate rocks at the Permian-Triassic boundary are rare, comparative studies on deep-water profiles were lacking for the major extinction event that occurred during this time. We present sections of different water depths in the Chibi area of southern China that we have selected for a comparative study. We analyzed carbon isotopes, calcium isotopes, as well as major and trace elements of carbonates from two sections (Chibi North and Chibi West) to obtain information on the volcanic activity, ocean acidification, as well as sea level rise and fall in the Chibi area during the mass extinction period. All carbon and calcium isotopes of carbonates from both sections are all negative after the mass extinction boundary. Carbonates from the Chibi North section have higher δ44/40Ca values and lower Sr/Ca ratios than the rocks from the Chibi West section. We propose that the negative bias of the calcium isotopes in the two sections result from diagenesis. Diagenesis transforms primary aragonite into calcite, showing the characteristics of high δ44/40Ca value and low Sr/Ca. By comparing our data with three published profiles of shallow-water carbonate rock, we recognize that calcium isotopes record gradients at different water depths. In the slope environment, the enhancement of pore fluid action near the coast caused an increase of the fluid buffer alteration, and we propose that a regression event occurred in the Chibi region during the Late Permian.
Continue reading ‘Characteristics of calcium isotopes at different water depths and their palaeoenvironmental significance for carbonate rocks of the Permian-Triassic boundary in Chibi, southern China’Characterization of undocumented CO2 hydrothermal vents in the Mediterranean Sea: implications for ocean acidification studies
Published 2 November 2022 Science ClosedTags: chemistry, field, Mediterranean, methods, vents
In this paper, we present the first multidisciplinary description of an undocumented hydrothermal field located in Sicily (Southern Tyrrhenian Sea), at water depths ranging from 0 to 5 m. The area and the associated living communities were visually explored (snorkeling and SCUBA diving) in June 2021. Twenty sites were investigated for pH, alkalinity and nutrients analysis. Geochemical investigation of hydrothermal fluids gases revealed CO2 dominance (98.1%) together with low amount of oxygen and reactive gases. Helium isotope ratios (R/Ra =2.51) and δ13CCO2 (3) seem to confirm an inorganic origin of hydrothermal degassing of CO2 and the ascent of heat and deep- seated magmatic fluids to the surface. Values of pH ranged between 7.84 and 8.04, ΩCa between 3.68 and 5.24 and ΩAr from 2.41 to 3.44. Visual census of fish and megabenthos revealed the presence of 62 species among which five protected by SPA/BIO Protocol and two by the International Union for Conservation of Nature. This study represents the first step for the description of a suitable area of considerable interest for future ocean acidification experimental studies.
Continue reading ‘Characterization of undocumented CO2 hydrothermal vents in the Mediterranean Sea: implications for ocean acidification studies’A look to the future acidified ocean through the eyes of the alien and invasive alga Caulerpa cylindracea (Chlorophyta, Ulvophyceae)
Published 18 October 2022 Science ClosedTags: adaptation, algae, biological response, field, morphology, otherprocess, photosynthesis, physiology, vents
Underwater CO2 vents represent natural laboratories where the responses of marine organisms to ocean acidification can be tested. In a such context, we investigated the changes in the physiology, anatomy, and ultrastructure of the non-indigenous algal species Caulerpa cylindracea growing along a natural pH/CO2 gradient, by conducting a reciprocal transplant experiment between two populations from an acidified vs a non-acidified site. Stress effects in transplants from current to lowered pH conditions resulted in a decrease in the number of active chloroplasts together with an increased number of dilatations between thylakoid membranes and a higher amount of plastoglobules. These changes were consistent with a decrease in the chlorophyll content and in photosynthetic efficiency, matched by an increase in carotenoid content and non-photochemical yields. On the opposite side, transplants from low to current pH showed a recovery to original conditions. Unexpectedly, no significant difference was recorded between wild populations living at current and lowered pH. These results suggest an ongoing acclimation process to lowered pH in the C. cylindracea populations growing in the vent area. This confirms the high plasticity of this invasive species, able to cope not only with different light and temperature conditions but even with a new acidified scenario.
Continue reading ‘A look to the future acidified ocean through the eyes of the alien and invasive alga Caulerpa cylindracea (Chlorophyta, Ulvophyceae)’
