CO2-driven seawater acidification differentially affects development and molecular plasticity along life history of fish (Oryzias latipes)

Fish early life stages have been shown to react sensitive to simulated ocean acidification. In particular, acid–base disturbances elicited by altered seawater carbonate chemistry have been shown to induce pathologies in larval fish. However, the mechanisms underlying these disturbances are largely unknown. We used gene expression profiling of genes involved in acid–base regulation and metabolism to investigate the effects of seawater hypercapnia on developing Japanese ricefish (medaka; Oryzias latipes). Our results demonstrate that embryos respond with delayed development during the time window of 2–5 dpf when exposed to a seawater pCO₂ of 0.12 and 0.42 kPa. This developmental delay is associated with strong down-regulation of genes from major metabolic pathways including glycolysis (G6PDH), Krebs cycle (CS) and the electron transport chain (CytC). In a second step we identified acid–base relevant genes in different ontogenetic stages (embryos, hatchlings and adults) and tissues (gill and intestine) that are up regulated in response to hypercapnia, including NHE3, NBCa, NBCb, AE1a, AE1b, ATP1a1a.1, ATP1a1b, ATP1b1a, Rhag, Rhbg and Rhcg. Interestingly, NHE3 and Rhcg expressions were increased in response to environmental hypercapnia in all ontogenetic stages and tissues tested, indicating the central role of these proteins in acid–base regulation. Furthermore, the increased expression of genes from amino acid metabolism pathways (ALT1, ALT2, AST1a, AST1b, AST2 and GLUD) suggests that energetic demands of hatchlings are fueled by the breakdown of amino acids. The present study provides a first detailed gene expression analysis throughout the ontogeny of a euryhaline teleost in response to seawater hypercapnia, indicating highest sensitivity in early embryonic stages, when functional ion regulatory epithelia are not yet developed.

Taxonomic composition and environmental distribution of post-extinction rhynchonelliform brachiopod faunas: constraints on short-term survival and the role of anoxia in the end-Permian mass extinction

Marine taxonomic losses during the end-Permian mass extinction were driven by physiological stresses from ocean warming, acidification, and anoxia that ultimately resulted from CO₂ release from Siberian Traps flood volcanism. Despite abundant proxy evidence for anoxia, its role is not well resolved because the timing and selectivity of the extinction are better explained by warming and ocean acidification. We studied the taxonomic composition and spatial and temporal distribution of brachiopod-rich post-extinction faunas, which contain short-lived Permian survivors that lived at a key time during and immediately after the peak of the extinction, to elucidate the controls on survival and the role of anoxia. Holdover brachiopods primarily belong to extinct families and orders, not to long-term survivors, and their probability of short-term survival was a function of pre-extinction metapopulation size. Although short-term survival appears to have been stochastic, likely because of intraspecific variation in tolerance within larger metapopulations, opportunistic and possibly dysaerobic-tolerant genera thrived locally. Rhynchonelliform brachiopod distribution was patchy, both environmentally and temporally. They were more abundant in shallow-water settings, consistent with an oxygenated habitable zone, and their local demise often corresponded with the local development of low-oxygen conditions. Thus, although warming and acidification may have been the primary triggers of taxonomic loss, the addition of spatially and temporally variable anoxic conditions exacerbated physiological stress and contributed to ultimate extinction of short-lived survivors. The combination of the three stresses – warming, acidification, and anoxia – which act synergistically to negatively affect respiratory physiology of marine invertebrates, may explain the severity of the end-Permian extinction and provides a sobering analogue for modern ocean acidification and anoxic dead zones.

Projected near-future levels of temperature and pCO2 reduce coral fertilization success

Increases in atmospheric carbon dioxide (pCO₂) are projected to contribute to a 1.1–6.4°C rise in global average surface temperatures and a 0.14–0.35 reduction in the average pH of the global surface ocean by 2100. If realized, these changes are expected to have negative consequences for reef-building corals including increased frequency and severity of coral bleaching and reduced rates of calcification and reef accretion. Much less is known regarding the independent and combined effects of temperature and pCO₂ on critical early life history processes such as fertilization. Here we show that increases in temperature (+3°C) and pCO₂ (+400 µatm) projected for this century negatively impact fertilization success of a common Indo-Pacific coral species, Acropora tenuis. While maximum fertilization did not differ among treatments, the sperm concentration required to obtain 50% of maximum fertilization increased 6- to 8- fold with the addition of a single factor (temperature or CO₂) and nearly 50- fold when both factors interact. Our results indicate that near-future changes in temperature and pCO₂ narrow the range of sperm concentrations that are capable of yielding high fertilization success in A. tenuis. Increased sperm limitation, in conjunction with adult population decline, may have severe consequences for coral reproductive success. Impaired sexual reproduction will further challenge corals by inhibiting population recovery and adaptation potential.

Advances in studies of ocean acidification

During the past 200 years, approximately one-half of the carbon dioxide from human activities is being taken up by the oceans. The uptake of carbon dioxide has led to a reduction of the pH value of surface seawater of 0.1 units, equivalent to a 30% increase in the concentration of hydrogen ions. If global emission of carbon dioxide from human activities continues to rise at the current rates, the average pH value of the oceans could fall by 0.5 units by the year 2100. This was equivalent to a three fold increase in the concentration of hydrogen ions. Global ocean acidification has become one of the most threatening disasters to the ocean ecosystem and has been attached great importance by the countries adjacent to oceans and the related international organizations in the world. In this paper the current situation and development of ocean acidification and the impacts of ocean acidification are described. It also summarizes the latest research achievements of ocean acidification and the ocean acidification studies in such countries as US, Europe, Japan, Australia, the Republic of Korea, and China, etc.

Changes in deep-water CO2 concentrations over the last several decades determined from discrete pCO2 measurements

Detection and attribution of hydrographic and biogeochemical changes in the deep ocean are challenging due to the small magnitude of their signals and to limitations in the accuracy of available data. However, there are indications that anthropogenic and climate change signals are starting to manifest at depth. The deep ocean below 2000 m comprises about 50% of the total ocean volume, and changes in the deep ocean should be followed over time to accurately assess the partitioning of anthropogenic carbon dioxide (CO₂) between the ocean, terrestrial biosphere, and atmosphere. Here we determine the changes in the interior deep-water inorganic carbon content by a novel means that uses the partial pressure of CO₂ measured at 20 °C, pCO₂(20), along three meridional transects in the Atlantic and Pacific oceans. These changes are measured on decadal time scales using observations from the World Ocean Circulation Experiment (WOCE)/World Hydrographic Program (WHP) of the 1980s and 1990s and the CLIVAR/CO₂ Repeat Hydrography Program of the past decade. The pCO₂(20) values show a consistent increase in deep water over the time period. Changes in total dissolved inorganic carbon (DIC) content in the deep interior are not significant or consistent, as most of the signal is below the level of analytical uncertainty. Using an approximate relationship between pCO₂(20) and DIC change, we infer DIC changes that are at the margin of detectability. However, when integrated on the basin scale, the increases range from 8–40% of the total specific water column changes over the past several decades. Patterns in chlorofluorocarbons (CFCs), along with output from an ocean model, suggest that the changes in pCO₂(20) and DIC are of anthropogenic origin.