The atmospheric partial pressure of CO2 (pCO2) is the key driver of climate variability. Boron isotopic compositions (δ11B) of marine calcium carbonates reveal pCO2 of the geologic past because boron isotope incorporation is sensitive to seawater pH, which closely reflects atmospheric pCO2. Biocarbonate δ11B values record environmental pH through a metabolic prism (so called “vital effects”), sometimes complicating interpretations. However, biocarbonate boron isotopes, coupled with boron concentrations (B/Ca), can also reveal the processes of calcification. Here, we review the link between seawater pH and the effective pH recorded by marine organisms via biomineralisation and summarise pCO2 reconstructions from boron isotopes for the Cenozoic (≈70 Ma to modern times), arguably the most significant contribution of this proxy system to date.
Continue reading ‘Boron proxies: from calcification site pH to Cenozoic pCO2 ‘Posts Tagged 'calcification'
Boron proxies: from calcification site pH to Cenozoic pCO2
Published 14 April 2025 Science ClosedTags: calcification, chemistry, paleo
Physiochemical responses of an asterinid starfish (Echinodermata: Asteroidea) to global ocean change
Published 20 January 2025 Science ClosedTags: biological response, calcification, echinoderms, laboratory, mortality, multiple factors, performance, physiology, temperature
The continuous increase in greenhouse gas (GHG) emissions, especially carbon dioxide (CO2), since the beginning of global industrialization has resulted in significant alterations in seawater physicochemical properties, particularly elevated seawater temperatures (ocean warming, OW) and ocean acidification (OA). These changes have wide-ranging consequences for marine organisms, affecting their biological functions and ecological roles. The combined effects of OW and OA may amplify adverse outcomes compared to individual stressors due to the complex reorganization of cellular mechanisms and molecular pathways, which subsequently appear in behavioral modifications. However, organismal reactions and thresholds to these stressors are variable, which might differ within organism ontogeny or among taxa, making predictions challenging. Therefore, increasing research has been performed to better understand the potential mechanisms underlying the ability of marine organisms to alleviate the effects of environmental change, mainly due to OW and OA. Thus, employing multiple bioindicators, specifically keystone species such as starfish, to evaluate the impacts of OW and OA offers a comprehensive approach to examining their effects not simply on the organism concerned but also on the broader ecosystem.
The presented studies in this thesis aim to contribute to the understanding the role of physiochemistry and trade-offs on marine ectotherms, particularly asterinid starfish, in coping with environmental stress. For this purpose, mineralogic, metabolic, behavioral, lipidomics, and enzymatic activity approaches are used. The research summarized in this thesis provides the first investigation of the effects of global ocean change on biomineralization and physiological traits through long-term experiments using asterinid starfish species, Aquilonastra yairi, distributed in tropical to subtropical regions (across the Mediterranean Sea, Red Sea, and Gulf of Suez). The starfish were exposed to two temperature levels (27 °C and 32 °C) crossed with three pCO2 regimes (455 µatm, 1052 µatm, and 2066 µatm), representing factorial combinations of ambient conditions and future levels of CO2 and temperature change according to the IPCC-Representative Concentration Pathways (RCPs) 8.5 greenhouse gas emission scenario for the year 2100.
The present work revealed that asterinid starfish demonstrate high stressor tolerance and resilience to increased temperature and pCO2 through adaptive adjustments in physiological functions or behavioral activities, suggesting high homeostatic capacities and the ability to regulate physiochemical response to maintain survival, fitness, and metabolic biosynthesis under chronic conditions. The temperature was the predominant factor, exerting a significant effect on the magnitude and frequency of the affected physiological-related processes; however, concurrent exposure to OA and OW stress produced synergistic effects on some of the starfish physiology-related responses tested. While decreased pH negatively affects starfish calcification performance, the increased temperature potentially mitigates these effects. However, increased temperature might also lead to more magnesium (Mg2+) incorporation into the calcite lattice, potentially compromising the starfish skeleton. Furthermore, it was revealed that starfish can preserve lipid-associated biochemistry (FAs) under elevated temperature and pCO2, which potentially provides molecular instruments to cope with future OA and OW scenarios. However, combined OA and OW significantly affected Ca-ATPase and Mg-ATPase enzyme activities, which are recognized to play an important role in the biomineralization pathway, raising concerns about potential susceptibilities in skeletal development and preservation.
Investigating the complex impacts of global ocean change on marine organisms requires a comprehensive research approach that encompasses diverse biological, chemical, and physical traits. Understanding the physiological and chemical responses of bioindicator species, e.g., asterinid starfish, to combined stressors OW and OA is important to comprehend the relationships and interactions between biological processes and abiotic environmental conditions, which in turn essential for accurately predicting their resilience, ecological implication, and broader ecosystem dynamics. At the ecosystem scale, this study significantly contributes to the ongoing knowledge for future studies of the impact of climate change on coral reef-associated invertebrates. Specifically, this finding is beneficial for the conservation of coral reef ecosystems under future ocean conditions.
Continue reading ‘Physiochemical responses of an asterinid starfish (Echinodermata: Asteroidea) to global ocean change’Short-term responses of native (Perna viridis, Linnaeus 1758) and non-native (Mytella strigata, Hanley 1843) mussels to independent and combined effects of lowered pH level and elevated temperature
Published 26 December 2024 Science ClosedTags: adaptation, biological response, BRcommunity, calcification, laboratory, mollusks, mortality, multiple factors, otherprocess, physiology, temperature
Changes in environmental conditions can influence the success of marine biological invasions. This study assessed the independent and combined acute short-term effects of increased temperature (OW) and lowered pH (OA) simulating future ocean conditions on a native, Perna viridis, and non-native, Mytella strigata, mussel species. There were four treatment combinations: Future (combination of ocean warming and ocean acidification), Ambient conditions, ocean acidification (OA), and ocean warming (OW). Survival and byssus thread regeneration in all treatments were measured daily for 7 days, while net calcification rate was calculated from the start and end of the experiment. Net calcification rate (NCR) was lowest under OA treatment. Likewise the low total alkalinity at the start of the experiment under OA suggests that the mussels experienced greater physiological stress. The higher survival rate of green mussels and the increase in the byssus regeneration rate over time in all treatments demonstrated that it can acclimate better to acute short-term temperature and pH stress. The very low survival of M. strigata in OA compared to other treatments indicates its high sensitivity to low pH stress. However, surviving charru individuals maintained high byssus thread regeneration in all treatments. Overall, results suggest that M. strigata may not displace the native green mussels’, P. viridis, higher tolerance to acute short-term exposure to elevated temperatures and low pH, but can co-exist in lower densities. This is the first study to compare the short-term physiological responses of a sympatric non-native and native mussel species under experimentally induced stress conditions. Longer-term studies on the population dynamics of these species are essential to assess the potential success of these species under changing and variable environmental conditions.
Continue reading ‘Short-term responses of native (Perna viridis, Linnaeus 1758) and non-native (Mytella strigata, Hanley 1843) mussels to independent and combined effects of lowered pH level and elevated temperature’Projections of coral reef carbonate production from a global climate coral reef coupled model
Published 17 December 2024 Science ClosedTags: biological response, BRcommunity, calcification, communitymodeling, corals, modeling, multiple factors, temperature
Coral reefs are under threat due to climate change and ocean acidification. However, large uncertainties remain concerning future carbon dioxide emissions, climate change and the associated impacts on coral reefs. While most previous studies have used climate model outputs to compute future coral reef carbonate production, we use a coral reef carbonate production module embedded in a global carbon-climate model. This enables the simulation of the response of coral reefs to projected changes in physical and chemical conditions at finer temporal resolution. The use of a fast-intermediate complexity model also permits the simulation of a large range of possible futures by considering different greenhouse gas concentration scenarios (Shared Socioeconomic Pathways (SSPs)), different climate sensitivities (hence different levels of warming for a given level of acidification), as well as the possibility of corals adapting their thermal bleaching thresholds. We show that without thermal adaptation, global coral reef carbonate production decreases to less than 25% of historical values in most scenarios over the twenty-first century, with limited further declines between 2100 and 2300 irrespective of the climate sensitivity. With thermal adaptation, there is far greater scenario variability in projections of reef carbonate production. Under high-emission scenarios the rate of twenty-first century declines is attenuated, with some global carbonate production declines delayed until the twenty-second century. Under high-mitigation scenarios, however, global coral reef carbonate production can recover in the twenty-first and twenty-second century, and thereafter persists at 50-90% of historical values, provided that the climate sensitivity is moderate.
Continue reading ‘Projections of coral reef carbonate production from a global climate coral reef coupled model’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’Effects of ocean acidification on abalone (Haliotis spp.) reproduction, early development, and growth: a review
Published 5 December 2024 Science ClosedTags: biological response, calcification, mollusks, morphology, mortality, physiology, reproduction, review, socio-economy
Abalone (Haliotis spp.) is a highly valuable and economically relevant marine commodity worldwide, with its production and value showing significant growth over the past two decades. Additionally, abalone hold essential ecological value by serving as a grazer and providing a microhabitat for various benthic organisms. Currently, seawater is experiencing a decrease in pH due to increased carbon dioxide (CO2) levels. It is projected that by 2100, the pH of seawater will decrease by approximately 0.3–0.4 units, with this trend continuing to 0.7–0.8 units by 2300. Abalone is particularly susceptible to ocean acidification due to its limited ability to maintain acid-base balance. Moreover, even if the effects on abalone are not lethal, world production values and ecosystem balance are likely to be impacted. This review examines the economic and ecological significance of abalone, as well as the morphological and physiological effects of ocean acidification on abalone during its early development, juvenile, and adult stages based on previous studies. In summary, the adverse effects of ocean acidification on abalone depend on several aspects, including the species, developmental stage, size, and duration of exposure.
Continue reading ‘Effects of ocean acidification on abalone (Haliotis spp.) reproduction, early development, and growth: a review’Varying effects of climate change on the photosynthesis and calcification of crustose coralline algae: implications for settlement of coral larvae
Published 4 December 2024 Science ClosedTags: algae, biological response, BRcommunity, calcification, corals, laboratory, molecular biology, multiple factors, photosynthesis, physiology, reproduction, temperature
Highlights
- Corals maintain settlement preferences under future climate conditions
- Future climate conditions negatively affect crustose coralline algae physiology
- Physiological responses to future climate conditions varied by algal species
Abstract
Coral recruitment is critical to the maintenance of healthy coral reef ecosystems. Many coral species settle preferentially on certain crustose coralline algae (CCA) (e.g., Hydrolithon boergesenii) over others (e.g., Paragoniolithon solubile). Calcifying organisms like CCA are particularly susceptible to ocean acidification (OA), and settlement behavior of larvae may be compromised as seawater temperatures increase (ocean warming; OW) and pH levels decrease as a result of climate change. Here, we examine the effects of future seawater conditions (OW and OA) on the calcification and photosynthetic efficiency of two CCA species, H. boergesenii and Pa. solubile. We also examine the effects of conditioning CCA in combined OA and OW on the settlement preferences of three coral species, Acropora palmata, A. cervicornis and Porites astreoides. Acropora palmata and Po. astreoides demonstrated a preference for H. boergesenii over Pa. solubile in choice experiments after short-term treatment (7–21 days) and this preference was not affected by future seawater conditions. A. cervicornis did not demonstrate a CCA preference under any treatment. Po. astreoides did not demonstrate a CCA preference in no-choice assays and settlement was unaffected by OW and OA even after the longest exposure (99 days). Both CCA had reduced photosynthetic efficiency after exposure to future seawater conditions. However, net calcification rate was reduced in H. boergesenii but not Pa. solubile after exposure to future seawater conditions. These results demonstrate that while climate change may differentially affect the physiological functioning of various species of CCA, coral settlement preferences are unlikely to be altered.
Continue reading ‘Varying effects of climate change on the photosynthesis and calcification of crustose coralline algae: implications for settlement of coral larvae’The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean
Published 25 November 2024 Science ClosedTags: algae, biological response, BRcommunity, calcification, corals, dissolution, field, laboratory, mitigation, North Atlantic, photosynthesis, primary production, respiration
The ongoing increase in anthropogenic CO₂ emissions since the industrial revolution has accelerated ocean acidification (OA) by introducing CO₂ into seawater, forming carbonic acid and reducing pH levels. This acidification threatens marine calcifiers by weakening their capacity to build calcium carbonate structures and promoting the dissolution of existing skeletons. Nonetheless, calcifying organisms may contribute to mitigating OA effects. This study explores the roles of corals (rolling Siderastrea radians, a seagrass dweller) and free-living calcifying coralline algae (back reef) in CO₂ mitigation in seawater. Field experiments were conducted on Isla Grande (Corales del Rosario and San Bernardo National Natural Park, Colombian Caribbean), to observe the diel variations in photosynthesis and calcification of these uncommon reef builders across different times of the day. Results demonstrate diel shifts influenced by photosynthesis/respiration and calcification/dissolution, with free-living coralline algae exhibiting higher productivity and calcification rates than corals during the day. Notably, free-living coralline algae displayed pronounced hysteresis, reflecting high sensitivity to light. These findings underscore the significant role of free-living coralline algae in marine carbon cycling, suggesting a more substantial impact on CO₂ mitigation than previously recognized. Conserving free-living coralline algae and their habitats is thus critical for supporting marine ecosystem health and resilience amidst global change, warranting further research into their metabolic responses to inform conservation strategies.
Continue reading ‘The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean’Effects of ocean acidification on the interaction between calcifying oysters (Ostrea chilensis) and bioeroding sponges (Cliona sp.)
Published 18 November 2024 Science ClosedTags: biological response, BRcommunity, calcification, community composition, dissolution, laboratory, mollusks, otherprocess, porifera, respiration
Ocean acidification can negatively affect a broad range of physiological processes in marine shelled molluscs. Marine bioeroding organisms could, in contrast, benefit from ocean acidification due to reduced energetic costs of bioerosion. Ocean acidification could thus exacerbate negative effects (e.g. reduced growth) of ocean acidification and shell borers on oysters. The aim of this study was to assess the impact of ocean acidification on the oyster Ostrea chilensis, the boring sponge Cliona sp., and their host-parasite relationship. We exposed three sets of organisms 1) O. chilensis, 2) Cliona sp., and 3) O. chilensis infested with Cliona sp. to pHT 8.03, 7.83, and 7.63. Reduced pH had no significant effect on calcification, respiration and clearance rate of uninfested O. chilensis. Low pH significantly reduced calcification leading to net dissolution of oyster shells at pHT 7.63 in sponge infested oysters. Net dissolution was likely caused by increased bioerosion by Cliona sp. at pHT 7.63. Additionally, declining pH and sponge infestation had a significant negative antagonistic effect (less negative than predicted additively) on clearance rate. This interaction suggests that sponge infested oysters increase clearance rates to cope with higher energy demand of increased shell repair resulting from higher boring activity of Cliona sp. at low seawater pH. O. chilensis body condition was unaffected by sponge infestation, pH, and the interaction of the two. The reduction in calcification rate suggests sponge infestation and ocean acidification together would exacerbate direct (reduced growth) and indirect (e.g., increased predation) negative effects on oyster health and survival. Our results indicate that ocean acidification by the end of the century could have severe consequences for marine molluscs with boring organisms.
Continue reading ‘Effects of ocean acidification on the interaction between calcifying oysters (Ostrea chilensis) and bioeroding sponges (Cliona sp.)’Genomic signals of adaptation to a natural CO2 gradient over a striking microgeographic scale
Published 14 November 2024 Science ClosedTags: adaptation, biological response, calcification, echinoderms, growth, laboratory, molecular biology, North Atlantic, otherprocess, physiology, vents
Highlights
- Arbacia lixula populations near CO2 vents show tolerance to acidification despite their vulnerable calcified structure.
- A. lixula population reveal genetic divergence and substructure in response to small-scale pH variation.
- Acidification potentially affects specific genes linked to growth, development, and calcification.
- lixula exhibits adaptability and plasticity to acidification, suggesting its potential resilience to cope with OA.
Abstract
Our study explores genomic signs of adaptation in A. lixula to different water pH conditions. To achieve this, we analysed the genomics variation of A. lixula individuals living across a natural pH gradient in Canary Islands, Spain. We use a 2b-RADseq protocol with 74 samples from sites with varying pH levels (from 7.3 to 7.9 during low tide) and included a control site. We identified 14,883 SNPs, with 432 identified as candidate SNPs under selection to pH variations through redundancy analysis. While all SNPs indicated genomic homogeneity, the 432 candidate SNPs under selection displayed genomic differences among sites and along the pH gradient. Out of these 432 loci, 17 were annotated using published A. lixula transcriptomes, involved in biological functions such as growth. Therefore, our findings suggest local adaptation in A. lixula populations to acidification in CO2 vents, even over short distances of 75 m, underscoring their potential resistance to future Ocean Acidification.
Continue reading ‘Genomic signals of adaptation to a natural CO2 gradient over a striking microgeographic scale’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’The dilemma of Luhuitou fringing reefs: net dissolution in winter and enhanced acidification in summer
Published 24 October 2024 Science ClosedTags: algae, calcification, chemistry, corals, North Pacific
Global coral reef ecosystems have been severely degraded due to the combined effects of climate change and human activities. Changes in the seawater carbonate system of coral reef ecosystems can reflect their status and their responses to the impacts of climate change and human activities. Winter and summer surveys in 2019 found that the ecological community of the Luhuitou coral reef flat was dominated by macroalgae and corals, respectively, contrasting with the conditions 10 years ago. The Luhuitou fringing reefs were sources of atmospheric CO2 in both seasons. In winter, the daily variation range of dissolved inorganic carbon (DIC) in Luhuitou coral reefs was up to 450 µmol/kg, while that of total alkalinity (TA) was only 68 µmol/kg. This indicated that the organic production was significantly higher than the calcification process during this period. The TA/DIC was approximately 0.15, which was less than half of that in healthy coral reefs; hence, photosynthesis-respiration processes were the most important factors controlling daily changes in the seawater carbonate system. The net community production (NCP) of the Luhuitou coral reef ecosystem in winter was as high as 47.65 mmol C/(m2·h). While the net community calcification (NCC) was approximately 3.35 and −4.15 mmol CaCO3/(m2·h) during the daytime and nighttime respectively. Therefore, the NCC for the entire day was −21.9 mmol CaCO3/(m2·d), indicating a net autotrophic dissolved state. In summer, the acidification was enhanced by thunderstorms and heavy rain with the highest seawater partial pressure of CO2 (pCO2) and lowest pHT. Over the past 10 years, the increase rate of seawater pCO2 in Luhuitou reef was approximately 13.3 µatm/a***, six times that of the open ocean, while the decrease rate of pH was approximately 0.008 3/a, being five times that of the global ocean. These findings underscore the importance of protecting and restoring Luhuitou fringing reef, as well as similar reefs worldwide.
Continue reading ‘The dilemma of Luhuitou fringing reefs: net dissolution in winter and enhanced acidification in summer’Chapter 1 – Overview: ocean acidification and marine mollusks
Published 18 October 2024 Science ClosedTags: biological response, BRcommunity, calcification, laboratory, mollusks, morphology, physiology, reproduction
Ocean acidification, resulting from elevated CO2 levels in the atmosphere, has considerable effects on marine mollusks. This chapter presents a comprehensive overview of the consequences of ocean acidification on marine mollusks, with a specific focus on gastropods, bivalves, and cephalopods. Mollusks with CaCO3-deposited shells are especially susceptible to ocean acidification, as it disrupts their calcification process. The diminished pH of seawater impedes the capability of marine mollusks to create and uphold their calcium carbonate shells, resulting in a decline in shell growth and overall shell strength. The extent of the reduction in calcification varies depending on the polycrystalline structure of CaCO3 secreted by the mollusks, their acid–base regulation, and their local physicochemical surroundings. Ocean acidification affects the physiological processes and metabolic rates of marine mollusks, potentially impacting their ability to allocate resources for calcification. It also negatively impacts reproduction, as ocean acidification increases the energy cost of physiological processes, consequently affecting energy allocation and reproductive capacity. The sustainability of shellfish populations is under threat from the adverse impacts of ocean acidification on mollusk reproduction and shell durability.
Continue reading ‘Chapter 1 – Overview: ocean acidification and marine mollusks’Low sensitivity of a heavily-calcified coccolithophore under increasing CO2: the case study of Helicosphaera carteri
Published 17 October 2024 Science ClosedTags: biological response, calcification, chemistry, laboratory, Mediterranean, morphology, paleo, physiology, phytoplankton
Studies on CO2 effects on coccolithophores, unicellular calcifying phytoplankton, show species-specific responses, although only less than 5 % of the ~280 living species have been tested so far. Helicosphaera carteri significantly contributes to carbon fluxes and CaCO3 storage due to its size and high calcite production. Despite its importance, few studies have examined H. carteri under experimental conditions, and only one has addressed the effects of rising CO2/decreasing pH. Being H. carteri a large-sized, obligated calcifier species, an important aspect to understand is how changes in seawater carbonate chemistry may affect its morphology. It has already been suggested for other coccolithophores species, that the presence of malformed coccoliths may represent a disadvantage for these organisms. Moreover, an alteration in coccolith morphology may affect their contribution to CaCO3 sedimentation and ballasting. As for H. carteri, it has also been suggested that due to its high PIC:POC ratio, the species could show a high-sensitivity to CO2 rise. In this study, we investigate for the first time whether high pCO2/low pH does affect the morphology of H. carteri coccoliths, by culturing this species under pre-industrial CO2 levels (~295 µatm) and ~600 µatm, i.e., the SSP 2-4.5 scenario for 2100 (IPCC, 2021). We also analyzed cellular PIC and POC quotas using morphometric data, roundness, and protoplast and coccosphere size to observe the pCO2 influence on the calcification and photosynthesis ratio.
Our results indicate that H. carteri morphology is only slightly affected by increasing CO2, in contrast to other heavily calcified species. Helicosphaera carteri protoplast and coccosphere shapes did not vary with changes in CO2, indicating unaltered general health. The low PIC:POC ratio found in this work for H. carteri compared to ratios previously measured in the same strain under different experimental conditions, and compared to other highly-calcified species, could explain the observed low sensitivity of H. carteri to CO2. Moreover, the observation of a stable ratio between calcification and photosynthesis in H. carteri under increasing CO2 might suggest a constant contribution to the rain ratio under climate change. However, further studies comparing experimental and field data from past ocean acidification events will be required to confirm the conclusions drawn here.
Continue reading ‘Low sensitivity of a heavily-calcified coccolithophore under increasing CO2: the case study of Helicosphaera carteri’Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification
Published 14 October 2024 Science ClosedTags: calcification, corals, North Pacific, physiology, primary production
Recovery of ecosystem function in the aftermath of climate extremes such as cyclones and marine heat waves occurs in contest of highly variable environmental conditions and more chronic disturbances such as ocean acidification, which can further alter community structure and function. The present study investigated short-term responses of reef-scale primary production (Net Ecosystem Production; NEP), calcification (Net Ecosystem Calcification; NEC) and community structure in 2018 and again five years later in 2022 on a coral reef flat in Lizard Island on Australia’s Great Barrier Reef, between and following multiple consecutive stressors, namely two cyclones (2014 and 2015) and back-to-back bleaching events (2016–2017 and 2020). NEC in 2022 was highly variable compared to what it was in 2018. Conversely, NEP was higher in 2022 even though light availability was often reduced by cloud cover. High variability in NEC indicated that environmental parameters may have immediate impacts on carbonate chemistry in seawater and may largely and quickly affect short-term recovery trajectories. Therefore, comparison of metabolic rates over short time scales across decades should be done with caution. We also found that cover of calcifiers and particularly algae were highest in coral rubble suggesting that typical benthic surveys in the open reef flat largely underestimate their abundance and possible contribution to NEP and NEC. This study adds to the evidence that NEC and NEP might not be exclusively related to coral cover and likely not tied to vertical reef accretion.
Continue reading ‘Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification’“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle
Published 7 October 2024 Science ClosedTags: algae, biological response, calcification, primary production, South Atlantic
Current evidence suggests that macroalgal-dominated habitats are important contributors to the oceanic carbon cycle, though the role of those formed by calcifiers remains controversial. Globally distributed coralline algal beds, built by pink coloured rhodoliths and maerl, cover extensive coastal shelf areas of the planet, but scarce information on their productivity, net carbon flux dynamics and carbonate deposits hampers assessing their contribution to the overall oceanic carbon cycle. Here, our data, covering large bathymetrical (2–51 m) and geographical ranges (53°N–27°S), show that coralline algal beds are highly productive habitats that can express substantial carbon uptake rates (28–1347 g C m−2 day−1), which vary in function of light availability and species composition and exceed reported estimates for other major macroalgal habitats. This high productivity, together with their substantial carbonate deposits (0.4–38 kilotons), renders coralline algal beds as highly relevant contributors to the present and future oceanic carbon cycle.
Continue reading ‘“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle’Skeletal magnesium content in Antarctic echinoderms along a latitudinal gradient
Published 4 October 2024 Science ClosedTags: Antarctic, biological response, BRcommunity, calcification, community composition, echinoderms, laboratory, otherprocess, physiology, respiration
Highlights
- Skeletal structures presented high Mg content, except in echinoid spines.
- Asteroids had the highest Mg content, followed by ophiuroids, holothuroids, and echinoids.
- No local variability in skeletal Mg content was observed in asteroids and holothuroids.
- Environmental parameters may have influenced the skeletal Mg in ophiuroids and echinoids.
Abstract
Ocean warming and acidification driven by anthropogenic CO2 emissions may impact the mineral composition of marine calcifiers. Species with high skeletal Mg content could be more susceptible in polar regions due to the increased solubility of CO2 at lower temperatures. We aimed to assess the environmental influence on skeletal Mg content of Antarctic echinoderms belonging to Asteroidea, Ophiuroidea, Echinoidea and Holothuroidea classes, along a latitudinal gradient from the South Shetland Islands to Rothera (Adelaide Island). We found that all skeletal structures, except for echinoid spines, exhibited high Mg content, with asteroids showing the highest levels. Our results suggest that asteroids and holothuroids exert a higher biological capacity to regulate Mg incorporation into their skeletons. In contrast, the variability observed in the skeletal Mg content of ophiuroids and echinoids appears to be more influenced by local environmental conditions. Species-specific differences in how environmental factors affect the skeletal Mg content can thus be expected as a response to global climate change.
Continue reading ‘Skeletal magnesium content in Antarctic echinoderms along a latitudinal gradient’Genome of Halimeda opuntia reveals differentiation of subgenomes and molecular bases of multinucleation and calcification in algae
Published 27 September 2024 Science ClosedTags: algae, biological response, calcification, laboratory, molecular biology
Significance
Coral reef ecosystems are undergoing significant degradation and reorganization due to ocean warming and acidification. Calcareous algae, crucial primary producers and reef-builders, exhibit diverse morphologies, lifestyles, and adaptative strategies. A significant gap exists, however, in deciphering the genetic basis of algae positioned at an evolutionary crossroad from unicellular to multicellular, from intracellular calcifying to extracellular calcification, and from acidification-sensitive to acidification-tolerant. Genome analysis of the green alga Halimeda opuntia and other algae shed light on unique genetic features associated with multinucleation, cell fragment regeneration, extracellular calcification, and tolerance of CO2 increases in seawater. Our findings advance the understanding of how calcareous algae respond to environmental changes and have implications in regenerative biology, plant grafting, and coral reef conservation and restoration.
Abstract
Algae mostly occur either as unicellular (microalgae) or multicellular (macroalgae) species, both being uninucleate. There are important exceptions, however, as some unicellular algae are multinucleate and macroscopic, some of which inhabit tropical seas and contribute to biocalcification and coral reef robustness. The evolutionary mechanisms and ecological significance of multinucleation and associated traits (e.g., rapid wound healing) are poorly understood. Here, we report the genome of Halimeda opuntia, a giant multinucleate unicellular chlorophyte characterized by interutricular calcification. We achieve a high-quality genome assembly that shows segregation into four subgenomes, with evidence for polyploidization concomitant with historical sea level and climate changes. We further find myosin VIII missing in H. opuntia and three other unicellular multinucleate chlorophytes, suggesting a potential mechanism that may underpin multinucleation. Genome analysis provides clues about how the unicellular alga could survive fragmentation and regenerate, as well as potential signatures for extracellular calcification and the coupling of calcification with photosynthesis. In addition, proteomic alkalinity shifts were found to potentially confer plasticity of H. opuntia to ocean acidification (OA). Our study provides crucial genetic information necessary for understanding multinucleation, cell regeneration, plasticity to OA, and different modes of calcification in algae and other organisms, which has important implications in reef conservation and bioengineering.
Continue reading ‘Genome of Halimeda opuntia reveals differentiation of subgenomes and molecular bases of multinucleation and calcification in algae’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’
