Join Academy presenter Aya to learn about ocean acidification: what it is; how it might impact coral reefs; and what we can do to help.
The California Academy of Sciences is a renowned scientific and educational institution dedicated to exploring, explaining, and sustaining life on Earth. Based in San Francisco’s Golden Gate Park, it’s the only place in the world to house an aquarium, planetarium, rainforest, and natural history museum—plus cutting-edge research programs—all under one living roof.
New research has shown that by injecting an alkalinizing agent into the ocean along the length of the Great Barrier Reef, it would be possible, at the present rate of anthropogenic carbon emissions, to offset ten years’ worth of ocean acidification.
The research, by CSIRO Oceans and Atmosphere, Hobart, used a high-resolution model developed for the Great Barrier Reef region to study the impact of artificial ocean alkalinization on the acidity of the waters in the Great Barrier Reef. The study is based on the use of existing shipping infrastructure to inject a source of alkalinity into the ocean, which could also be considered as an acceleration of the chemical weathering of minerals through natural processes. Their results are published today (June 8, 2021) in the IOP Publishing journal Environmental Research Letters.
The Great Barrier Reef (GBR) is a globally significant coral reef system supporting productive and diverse ecosystems. The GBR is under increasing threat from climate change and local anthropogenic stressors, with its general condition degrading over recent decades. In response to this, a number of techniques have been proposed to offset or ameliorate environmental changes. In this study, we use a coupled hydrodynamic-biogeochemical model of the GBR and surrounding ocean to simulate artificial ocean alkalinisation (AOA) as a means to reverse the impact of global ocean acidification on GBR reefs. Our results demonstrate that a continuous release of 90 000 t of alkalinity every 3 d over one year along the entire length of the GBR, following the Gladstone-Weipa bulk carrier route, increases the mean aragonite saturation state (Ωar) across the GBR’s 3860 reefs by 0.05. This change offsets just over 4 years (∼4.2) of ocean acidification under the present rate of anthropogenic carbon emissions. The injection raises Ωar in the 250 reefs closest to the route by ⩾0.15, reversing further projected Ocean Acidification. Following cessation of alkalinity injection Ωar returns to the value of the waters in the absence of AOA over a 6 month period, primarily due to transport of additional alkalinity into the Coral Sea. Significantly, our study provides for the first time a model of AOA applied along existing shipping infrastructure that has been used to investigate shelf scale impacts. Thus, amelioration of decades of OA on the GBR is feasible using existing infrastructure, but is likely to be extremely expensive, include as yet unquantified risks, and would need to be undertaken continuously until such time, probably centuries in the future, when atmospheric CO2 concentrations have returned to today’s values.
After the industrial revolution, increasing anthropogenic CO2 emission causes a number of changes in seawater. These changes are known as ocean acidification and affect the seaweeds in various ways. Therefore, this study is aimed to determine the ecological succession of Ulva flexuosa Wulfen 1803 in future predicted CO2-induced low pH conditions alone and in combination with naturally relevant ultraviolet radiation (UVR). For this purpose, acidification experiments with and without UVR were conducted on U. flexuosa from the Mediterranean coast, and important physiological features of algae was investigated. In this study, the Fv/Fm ratios of U. flexuosa ranged from 0.718±0.01 to 0.754±0.009. While rETRmax values of samples exposed to elevated-CO2 were measured between 112.13 – 151.93 µmol e–m-2s-1, it was determined between 111.7 – 158.4 µmol e–m-2s-1 in samples exposed to ambient sea water. According to our results, increased CO2 concentration in seawater did not improve the photosynthetic efficiency of U. flexuosa. However, when the specimens were exposed to elevated-CO2, nitrate reductase activity of U. flexuosa was declined drastically. According to the results, it is suggested that the elevated CO2 may regulate the nitrogen preference of U. flexuosa. Besides, the data also show that U. flexuosa was not sensitive to UVR.
Climate change is at the forefront of today’s global challenges with its potential to turn into a runaway process. Fishing pressure acts in concert and exacerbates the impacts of climate change. The North Atlantic Ocean is no exemption of the increasing anthropogenic stress with Atlantic cod, Gadus Morhua, one of its most prominent fish species, displaying the ocean’s state. Most Atlantic cod stocks have experienced high rates of fishing and biomass declines, leading to renovation of fishing regulations and the implementation of rebuilding strategies. Today, the cod stocks differ considerably in trends and commercial status with 8 stocks considered collapsed and 57 % of today’s landings supplied by one single stock, the North East Arctic cod. What drives the collapse and what drives the recovery of a stock? Elucidating drivers of Atlantic cod productivity at low abundance is inevitable for sustainably managing the species in its changing habitat. This thesis attempts a comprehensive study on climate change impacts by addressing rising ocean temperature (paper I-III), temperature variability (paper II), acidification (paper III) and uncertainty (of the biology and as risk in management under the precautionary approach [paper IV]). Individual and synergistic impacts of climate change are discussed with a particular focus on nonlinear dynamics, including the potential for Allee effects (paper I-III). Allee effects describe the decrease in per capita growth rate at small population size, which can hinder population recovery by reinforcing degradation. Such a shift in the underlying biology can be irreversible and demands proactive and precautionary management measures. Application of precautionary measures to protect the environment and manage risks in situations of high uncertainty is a central tenet of the “precautionary approach”, a guiding principle in fisheries management. The poor state of various commercial fish stocks worldwide stands in contrast to the precautionary approach and suggests a subordinate role of science in fisheries management. In paper IV, Canada’s fisheries policy and advisory process is contrasted with the EU’s Common Fisheries Policy in regard to the precautionary approach and the role of science, in order to identify policy and institutional constraints that have hindered sustainable, precautionary management practices. Drawing from insights on climate change driven productivity changes (paper I-III) and the importance of a policy and institutional framework that acknowledges these (paper IV), this thesis ends with suggestions for scientifically informed, precautionary and sustainable fisheries management practices that can speed up recovery and allow for a vital fishery in the future.
The SDG Bergen Policy Brief series is a novel and innovative way to communicate with policy-makers to engage with the Sustainable Development Goals (SDGs). The goal being to secure more research-based decision-making.
NEW POLICY BRIEF: Leader Benjamin Pfeil (to the right) of the Bjerknes Climate Data Centre is first author of SDG Bergen Policy Brief #1, advising on ocean acidification and SDG14, Life below water. Here he is pictured with SDG Bergen Science Advice’s Scientific Director Edvard Hviding displaying the policy brief, the first in a series. Photo: Sverre Ole Drønen, UiB.
The launch of the SDG Bergen Policy Brief series on World Ocean Day 2021 is yet another outlet for the University of Bergen (UiB) to innovate in its communication directed at policy-makers and one another contribution from the university towards the UN Ocean Decade.
Creating innovative communication channels
“We have long worked towards the UN system, national governments and with partners globally to reach policy-makers on a number of levels,” says Scientific Director Edvard Hviding of SDG Bergen Science Advice.
In June 2017, then Rector Dag Rune Olsen sent off a delegation to the first UN Ocean Conference, where a successful side event raised the University of Bergen’s SDG oriented profile. After this, Rector Olsen asked Hviding to start work to establish SDG Bergen.
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A sustainable ocean for first policy brief
SDG Bergen Policy Brief #1 contains three policy recommendations to avoid ocean acidification based on data provided by data analysts and researchers from UiB, the Bjerknes Centre for Climate Research, NORCE, ICOS and the Institute for Marine Research. The data presented in the policy brief has been provided to IOC-UNESCO (Intergovernmental Oceanographic Commission).
“On behalf of all the authors, I’m extremely proud that our data assessment to combat ocean acidification has become the first SDG Bergen Policy Brief. This recognises our work to provide the world with ocean acidification data. I hope our recommendations provide policy-makers with science-based knowledge to make decisions to save our ocean,” says Leader Benjamin Pfeil of the Bjerknes Climate Data Centre.
It’s no surprise the first SDG Bergen Policy Brief deals with ocean science. UiB has a long ocean research tradition and was recently ranked top 10 for oceanography by the Shanghai Ranking. The university has also been appointed SDG14 Hub for United Nations Academic Impact (UNAI).
“Due to our global leadership role on SDG14, it was only logical for the first SDG Bergen Policy Brief to be ocean-oriented,” says Hviding, “not the least to show the partnership across institutions in the Bergen area when it comes to data analysis and research on ocean acidification.”
UN recognition for new policy brief series
The idea to create a series of SDG oriented policy briefs has met with acclaim in the UN system and internationally.
“The first SDG Bergen Policy Brief addresses challenges in data flow and data availability in respect to SDG target submissions to alleviate a situation of incomplete, disorganized or simply unavailable data. As the world works to harness the vastness and mysteries of the ocean to sustainable human purpose, the work of SDG Bergen continues to explore those possibilities,” says the first UNAI Chief Ramu Damodaran, who retired on 1 June 2021.
Damodaran has been involved in appointing the University of Bergen as UNAI’s SDG14 Hub.
IOC-UNESCO is the custodian agency for the SDG indicator 14.3.1 focusing on ocean acidification measurements in the open ocean and coastal seas.
“We welcome the support by Norway to provide both data and outreach to combat ocean acidification. The first SDG Bergen Policy Brief will help raise awareness among policy-makers, civil society and business stakeholders on the importance of ocean acidification observation and science to mitigate and adapt to ocean acidification, contributing to the sustainable use of ocean resources,” says Dr. Kirsten Isensee, who is a programme specialist at IOC-UNESCO
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Sverre Ole Dronen, University of Bergen, 8 June 2021. Article.
SDG Bergen Policy Brief #1 – A sustainable ocean: providing data to assess ocean acidification – is out on 8 June 2021 (World Ocean Day). Read the policy brief here.
Corals in the Maldives suffering massive bleaching from heat stress in May 2016. (Keystone/The Ocean Agency/XL Catlin Seaview Survey via AP)
As the world celebrates World Ocean Day, a new high in levels of carbon dioxide in the air will have damaging effects on marine life.
Levels of carbon dioxide concentration in the atmosphere rose to record highs in May, causing a “serious impact on oceans”, the World Meteorological Organisation (WMO) said on Tuesday.
The Mauna Loa Observatory in Hawaii recorded a monthly average of 419.13 parts per million (ppm), a rise from 417.31 ppm in May 2020. Carbon dioxide is one of the key greenhouse gases emitted through human activities, primarily from burning fossil fuels. It is a major driver of global warming, contributing to more extreme weather events, ice melting, sea level rise and ocean acidification.
Today is World Oceans Day; a time to highlight human impact on the health of our oceans. In recent years, we have become increasingly aware of the amount of carbon dioxide (CO2) that human activity is releasing into the Earth’s atmosphere. What is less well known, is that one third of anthropogenic carbon emissions are absorbed from the atmosphere by Earth’s oceans. While this helps to reduce the amount of CO2 that stays in the atmosphere, it also has an impact on ocean chemistry. The increased amount of CO2 in seawater lowers the pH of the ocean, making it more acidic. This process is known as ocean acidification and disrupts the marine carbonate system.
It’s currently not possible to directly measure pH from space, and proxies like temperature, salinity, and biological activity are used to infer changes in acidity. During my Fellowship placement in the Ocean Biogeochemistry (OceanBug) group at the University of Oxford, I am using the experience I gained during my PhD looking for subtle organic signatures on Mars to find ways to directly detect acid in seawater. Using laboratory analogue experiments, as I did for Martian studies, we hope to establish detectability limits for boric acid in seawater samples, to combine in-situ pH measurements with satellite data to interpret historical trends and develop new ways of monitoring ocean acidification from space to better inform scientists, policy makers and the public about how we can protect our oceans.
Global map of ocean alkalinity created using temperature and salinity measurements (averaged between 2010 and 2014) from several satellites, including ESA’s SMOS mission. Source: Ifremer/ESA/CNES
Project title:Biogenic volatile organic compound (BVOC) emissions from coral reefs under stress
Description: Biogenic volatile organic compounds (BVOCs) are trace gases of biological origin that play a key role in earth system processes. There are two principal aspects relating to climate change and BVOCs (1) the potential influence of BVOC’s on regional and global climate, and (2) the potential influence of a changing climate on the production of BVOCs. An inter-reliance which is well illustrated on the Great Barrier Reef.
Coral reefs are considered potential hotspots for BVOC emissions due to their high biological productivity, temperature and light, but little is known about the amount or forms of BVOCs emitted, and the mechanisms underlying their production. BVOCs can all act as precursors of secondary organic aerosols, essential for particle nucleation and the production of cloud condensation nuclei, which seed cloud droplets and influence the properties including the albedo (reflectivity) of low level clouds, potentially playing a role in regulating climate.
The production of BVOCs by coral reefs is also a poorly understood potential feedback mechanism in coral bleaching episodes. Some studies have suggested that production of BVOCs by the Great Barrier Reef may help to down-regulate solar irradiance and sea surface temperatures, mitigating against bleaching, while others argue this effect may not be significant, or exist at all. Compounding this ongoing debate, changes to BVOCs production as a result of warming and associated coral bleaching (and other stressors such as light and ocean acidification) in the Great Barrier Reef remain almost completely unquantified.
One of the major problems with BVOC research on coral reefs to-date is that seawater BVOC samples are collected in a bottle and then analysed back in the laboratory. This limits the number of BVOCs measured, and the quality, and temporal resolution, of the data. This project will overcome these previous limitations by using a transportable Equilibrator Inlet Proton Transfer Reaction Mass to make in situ, high precision, high temporal resolution measurements of the full spectrum of BVOCs. As such, it will make significant advances in quantifying and understanding the mechanisms of BVOC release from coral reefs and their influence on the regional and global climate system.
This project is part of the Reef Restoration and Adaptation Program (RRAP), a large-scale collaborative research and development program to develop, test and assess innovative interventions to enhance reef resilience and sustain ecological functions and values. The Cooling and Shading sub-program is focused on evaluation and development of interventions to reduce coral bleaching stress across multiple scales, ranging from individual high value reefs right up to the scale of the entire GBR ecosystem. This program incorporates fundamental science on atmospheric – radiation – ocean – coral interactions as well as applied science and engineering in the development and testing of innovative coral conservation approaches.
Eligibility: Applicants will need to have an Honours or Master degree, undertaken in English, in a related field such as biogeochemistry, environmental chemistry, or closely related. The project will involve extended periods in the field, including in boats, sometimes in remote areas. The PhD scholarship will provide a tax-free stipend of $28,082 and tuition fees will be exempt. Interested applicants should send their CV highlighting their research background and interests in this area to Prof. Bradley Eyre – (bradley.eyre@scu.edu.au). Only short-listed applicants will be notified. Closing date July 11, 2021 although it may be extended longer if position is not filled. Starting date is November 2021 (for overseas applicants this will depend on Australian boarders and getting appropriate visas).
The project will be undertaken in the Centre for Coastal Biogeochemistry (www.scu.edu.au/coastal-biogeochemistry) at Southern Cross University which received the highest rank of 5.0, well above world average, in geochemistry in the most recent assessment of research excellence by the Australian government.
This position is based at Southern Cross University’s Lismore campus, northern NSW, Australia (near Byron Bay). The region is a great place to live with a sub-tropical climate, some the best beaches and surfing in the world, plus great fishing, scuba diving and wilderness areas. The quality of life is high and the cost of living relatively low compared to many cities.
Celebrate #UNWorldOceansDay with the United Nations and Oceanic Global on 8 June! Learn about new ways to protect our blue planet and hear from thought-leaders, experts, ocean advocates, entrepreneurs, and community voices as they highlight the importance of the ocean for sustaining life and livelihoods. Featuring Dr. Sylvia Earle, Gael Garcia Bernal, EARTHGANG, Brian Skerry, Nathalie Kelley, Danni Washington, Amanda Cerny, Angelique Kidjo, Bomba Estereo, Catarina Lorenzo, OceanX, Céline Semaan, and many more! UN World Oceans Day is a free, digital event streaming from 10AM-5PM EDT at UNWorldOceansDay.org on 8 June! This event is hosted by the United Nations Division for Ocean Affairs and the Law of the Sea, Office of Legal Affairs, in partnership with Oceanic Global, Blancpain, and La Mer. This film is narrated by the incredible oceanographer Dr. Sylvia Earle, who will be speaking at this year’s event to outline the relationship between the ocean and human health and well-being.
Professor Tim Stephens on World Ocean Day 2021Share
For World Ocean Day 2021, Professor Tim Stephens speaks about the key role of law in environmental protection.
Today is World Ocean Day — a day to encourage people everywhere to celebrate and take action for our shared ocean.
The 2021 World Ocean conservation action focus is to support and grow the “30×30” global movement to protect at least 30% of our blue planet by 2030.
We had a chat to Sydney Law School’s Professor Tim Stephens about his research into ocean acidification and the role of national and international law in regulating human impact on marine ecosystems.
Larval white seabass were lab-exposed to elevated CO2 levels simulating future ocean acidification (OA).
Exposure to OA did not induce any changes in ion-transporting capacity, aerobic respiration rate, or total length of larval white seabass.
Retroactive analysis of the water in broodstock tanks revealed the parents had been chronically exposed to elevated CO2 levels, which may have affected the physiology of the larvae and conferred the observed resilience.
Abstract
Ocean acidification (OA) has been proposed to increase the energetic demand for acid-base regulation at the expense of larval fish growth. Here, white seabass (Atractoscion nobilis) eggs and larvae were reared at control (542 ± 28 μatm) and elevated pCO2 (1,831 ± 105 μatm) until five days post-fertilization (dpf). Skin ionocytes were identified by immunodetection of the Na+/K+-ATPase (NKA) enzyme. Larvae exposed to elevated pCO2 possessed significantly higher skin ionocyte number and density compared to control larvae. However, when ionocyte size was accounted for, the relative ionocyte area (a proxy for total ionoregulatory capacity) was unchanged. Similarly, there were no differences in relative NKA abundance, resting O2 consumption rate, and total length between control and treatment larvae at 5 dpf, nor in the rate at which relative ionocyte area and total length changed between 2–5 dpf. Altogether, our results suggest that OA conditions projected for the next century do not significantly affect the ionoregulatory capacity or energy consumption of larval white seabass. Finally, a retroactive analysis of the water in the recirculating aquarium system that housed the broodstock revealed the parents had been exposed to average pCO2 of ~1,200 μatm for at least 3.5 years prior to this experiment. Future studies should investigate whether larval white seabass are naturally resilient to OA, or if this resilience is the result of parental chronic acclimation to OA, and/or from natural selection during spawning and fertilization in elevated pCO2.
Environmental triclosan levels alter the reproductive output of R. philippinarum.
Environmental triclosan levels reduce body mass in R. philippinarum.
R. decussatus growth was resilient to environmental changes.
Worst case scenario (TCS and climate change) will affect Manila clam production.
Abstract
We built a simulation model based on Dynamic Energy Budget theory (DEB) to assess the growth and reproductive potential of the native European clam Ruditapes decussatus and the introduced Manila clam Ruditapes philippinarum under current temperature and pH conditions in a Portuguese estuary and under those forecasted for the end of the 21st c. The climate change scenario RCP8.5 predicts temperature increase of 3 °C and a pH decrease of 0.4 units. The model was run under additional conditions of exposure to the emerging contaminant triclosan (TCS) and in the absence of this compound. The parameters of the DEB model were calibrated with the results of laboratory experiments complemented with data from the literature available for these two important commercial shellfish resources. For each species and experimental condition (eight combinations), we used data from the experiments to produce estimates for the key parameters controlling food intake flux, assimilation flux, somatic maintenance flux and energy at the initial simulation time. The results showed that the growth and reproductive potential of both species would be compromised under future climate conditions, but the effect of TCS exposure had a higher impact on the energy budget than forecasted temperature and pH variations. The egg production of R. philippinarum was projected to suffer a more marked reduction with exposure to TCS, regardless of the climatic factor, while the native R. decussatus appeared more resilient to environmental causes of stress. The results suggest a likely decrease in the rates of expansion of the introduced R. philippinarum in European waters, and negative effects on fisheries and aquaculture production of exposure to emerging contaminants (e.g., TCS) and climate change.
Elevated CO2 altered behaviour in zebrafish but not in an additive manner.
Acclimations to ~900, 2200, and 4200 μatm cause increased, normal, and decreased anxiety-like behaviour.
Exploratory behaviour was not affected by any CO2 treatment.
Elevated CO2 to ~4200 μatm decreased locomotion.
Abstract
CO2-induced aquatic acidification is predicted to affect fish neuronal GABAA receptors leading to widespread behavioural alterations. However, the large variability in the magnitude and direction of behavioural responses suggests substantial species-specific CO2 threshold differences, life history and parental acclimation effects, experimental artifacts, or a combination of these factors. As an established model organism, zebrafish (Danio rerio) can be reared under stable conditions for multiple generations, which may help control for some of the variability observed in wild-caught fishes. Here, we used two standardized tests to investigate the effect of 1-week acclimatization to four pCO2 levels on zebrafish anxiety-like behaviour, exploratory behaviour, and locomotion. Fish acclimatized to 900 μatm CO2 demonstrated increased anxiety-like behaviour compared to control fish (~480 μatm), however, the behaviour of fish exposed to 2200 μatm CO2 was indistinguishable from that of controls. In addition, fish acclimatized to 4200 μatm CO2 had decreased anxiety-like behaviour; i.e. the opposite response than the 900 μatm CO2 treatment. On the other hand, exploratory behaviour did not differ among any of the pCO2 exposures that were tested. Thus, zebrafish behavioural responses to elevated pCO2 are not linear; with potential important implications for physiological, environmental, and aquatic acidification studies.
The late spring EcoMon cruise accomplished their objectives and more in two weeks at sea. From bongo tows, water casts and ocean acidification work to bird observing and shrunken cups, it was a productive cruise.
We have completed our sampling on the Spring Ecosystem Monitoring Survey with our 106th station located just under 60 nautical miles east of Cape Cod.
Mission Accomplished
The cruise was very successful. We accomplished two objectives in addition to our primary monitoring protocols. The first was to sample ocean acidification stations in the Gulf of Maine. We did not sail last year because of the pandemic, and these stations have often been difficult to reach due to time constraints on previous surveys. On this cruise we only missed two of these stations: one in the northern Gulf of Maine and one in the central Gulf of Maine.
The second objective was to sample mackerel eggs and larvae in the western Gulf of Maine and Southern New England waters, the places they are likely to be this time of year. When storms were forecast for Georges Bank, we shifted the cruise track to the western Gulf of Maine. This allowed our ship, the NOAA Ship Gordon Gunter, to keep working. As a result we exceeded our planned coverage of the western Gulf of Maine, although we only partially sampled Georges Bank.
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Snails and Slugs to Further Ocean Acidification Work
The work on collecting pteropods—free-swimming pelagic sea snails and sea slugs—has continued throughout the cruise. Betsy Broughton has been an avid “pteropod hunter.” She worked with Chris Taylor, who would grab simultaneous dissolved inorganic carbon (DIC) samples from our scientific seawater collection system to match with them. Tamara Holzwarth-Davis and Paula Fratantoni, both on the other watch, did the same. Together they collected 34 samples of pteropods with matching DIC data, which should be great data for this ocean acidification effects study.
Applications are invited from suitably qualified candidates for a full-time fixed term position as a Postdoctoral Researcher with the School of Natural Sciences/Ryan Institute at the National University of Ireland, Galway. This position is with the CE2COAST™ project funded through JPI Oceans and JPI Climate and is available for 12 months, commencing on or after the 1st August 2021
The Ryan Institute is the National University of Ireland, Galway’s hub for Environmental, Marine and Energy research and contributes to some of the most important national and international, long-term, environmental, marine and energy research issues (http://www.nuigalway.ie/ryaninstitute/). Staff from a range of disciplines and schools across the University contribute to research in the Institute. Staff in the School of Natural Sciences are the main contributors to the project with which this post is associated. The CE2COAST project is funded through JPI Oceans and JPI Climate with NUI Galway and the Marine Institute as the Irish partners – see https://www.ce2coast.com/.
Applications are invited from suitably qualified candidates for a full-time fixed term position as a Research Assistant with the School of Natural Sciences /Ryan Institute at the National University of Ireland, Galway.
This position is with the CE2COAST™ project funded through JPI Oceans and JPI Climate and is available for 12 months, commencing on or after the 1st August 2021.
The Ryan Institute is the National University of Ireland, Galway’s hub for Environmental, Marine and Energy research and contributes to some of the most important national and international, long-term, environmental, marine and energy research issues (http://www.nuigalway.ie/ryaninstitute/). Staff from a range of disciplines and schools across the University contribute to research in the Institute. Staff in the School of Natural Sciences are the main contributors to the project with which this post is associated. The CE2COAST project is funded through JPI Oceans and JPI Climate with NUI Galway and the Marine Institute as the Irish partners – see https://www.ce2coast.com/.
Biomineralization is one of the key processes that is notably affected in marine calcifiers such as oysters under ocean acidification (OA). Understanding molecular changes in the biomineralization process under OA and its heritability, therefore, is key to developing conservation strategies for protecting ecologically and economically important oyster species. To do this, in this study, we have explicitly chosen the tissue involved in biomineralization (mantle) of an estuarine commercial oyster species, Crassostrea hongkongensis. The primary aim of this study is to understand the influence of DNA methylation over gene expression of mantle tissue under decreased ~pH 7.4, a proxy of OA, and to extrapolate if these molecular changes can be observed in the product of biomineralization—the shell. We grew early juvenile C. hongkongensis, under decreased ~pH 7.4 and control ~pH 8.0 over 4.5 months and studied OA-induced DNA methylation and gene expression patterns along with shell properties such as microstructure, crystal orientation and hardness. The population of oysters used in this study was found to be moderately resilient to OA at the end of the experiment. The expression of key biomineralization-related genes such as carbonic anhydrase and alkaline phosphatase remained unaffected; thus, the mechanical properties of the shell (shell growth rate, hardness and crystal orientation) were also maintained without any significant difference between control and OA conditions with signs of severe dissolution. In addition, this study makes three major conclusions: (1) higher expression of Ca2+ binding/signalling-related genes in the mantle plays a key role in maintaining biomineralization under OA; (2) DNA methylation changes occur in response to OA; however, these methylation changes do not directly control gene expression; and (3) OA would be more of a ‘dissolution problem’ rather than a ‘biomineralization problem’ for resilient species that maintain calcification rate with normal shell growth and mechanical properties.
Rajan K. C., Meng Y., Yu Z., Roberts S. B. & Vengatesen T., in press. Oyster biomineralization under ocean acidification: from genes to shell. Global Change Biology. Article (subscription required).
Regulation of ionic composition and pH is a requisite of all digestive systems in the animal kingdom. Larval stages of the marine superphylum Ambulacraria, including echinoderms and hemichordates, were demonstrated to have highly alkaline conditions in their midgut with the underlying epithelial transport mechanisms being largely unknown. Using ion-selective microelectrodes, the present study demonstrated that pluteus larvae of the purple sea urchin have highly alkaline pH (pH ∼9) and low [Na+] (∼120 mmol l−1) in their midgut fluids, compared with the ionic composition of the surrounding seawater. We pharmacologically investigated the role of Na+/H+ exchangers (NHE) in intracellular pH regulation and midgut proton and sodium maintenance using the NHE inhibitor 5-(n-ethyl-n-isopropyl)amiloride (EIPA). Basolateral EIPA application decreased midgut pH while luminal application via micro-injections increased midgut [Na+], without affecting pH. Immunohistochemical analysis demonstrated a luminal localization of NHE-2 (SpSlc9a2) in the midgut epithelium. Specific knockdown of spslc9a2 using Vivo-Morpholinos led to an increase in midgut [Na+] without affecting pH. Acute acidification experiments in combination with quantitative PCR analysis and measurements of midgut pH and [Na+] identified two other NHE isoforms, Spslc9a7 and SpSlc9a8, which potentially contribute to the regulation of [Na+] and pH in midgut fluids. This work provides new insights into ion regulatory mechanisms in the midgut epithelium of sea urchin larvae. The involvement of NHEs in regulating pH and Na+ balance in midgut fluids shows conserved features of insect and vertebrate digestive systems and may contribute to the ability of sea urchin larvae to cope with changes in seawater pH.
