Ocean acidification may increase calcification rates, but at a cost

Ocean acidification is the lowering of pH in the oceans as a result of increasing uptake of atmospheric carbon dioxide. Carbon dioxide is entering the oceans at a greater rate than ever before, reducing the ocean's natural buffering capacity and lowering pH. Previous work on the biological consequences of ocean acidification has suggested that calcification and metabolic processes are compromised in acidified seawater. By contrast, here we show, using the ophiuroid brittlestar Amphiura filiformis as a model calcifying organism, that some organisms can increase the rates of many of their biological processes (in this case, metabolism and the ability to calcify to compensate for increased seawater acidity). However, this upregulation of metabolism and calcification, potentially ameliorating some of the effects of increased acidity comes at a substantial cost (muscle wastage) and is therefore unlikely to be sustainable in the long term.     

Resolving the interactions of ocean acidification and temperature on coral calcification media pH

Coral Reefs - Ocean acidification typically reduces the calcification rates of massive Porites spp. corals, but increasing seawater temperatures (below the stress and bleaching threshold) can...     

Ocean acidification alters the thermal performance curves of brooded larvae from the reef coral Pocillopora damicornis

Coral Reefs - Establishing the thermal reaction norm of coral larvae under elevated pCO2 is crucial to anticipate how larval dispersal and population maintenance may be affected by future climate...     

Mechanical robustness of the calcareous tubeworm Hydroides elegans: warming mitigates the adverse effects of ocean acidification

Development of antifouling strategies requires knowledge of how fouling organisms would respond to climate change associated environmental stressors. Here, a calcareous tube built by the tubeworm, Hydroides elegans, was used as an example to evaluate the individual and interactive effects of ocean acidification (OA), warming and reduced salinity on the mechanical properties of a tube. Tubeworms produce a mechanically weaker tube with less resistance to simulated predator attack under OA (pH 7.8). Warming (29°C) increased tube volume, tube mineral density and the tube’s resistance to a simulated predatory attack. A weakening effect by OA did not make the removal of tubeworms easier except for the earliest stage, in which warming had the least effect. Reduced salinity (27 psu) did not affect tubes. This study showed that both mechanical analysis and computational modeling can be integrated with biofouling research to provide insights into how fouling communities might develop in future ocean conditions.     

Effect of short-term subaerial exposure on the cauliflower coral,Pocillopora damicornis,during a simulated extreme low-tide event

Coral Reefs - There is increased interest in understanding how stress reduces coral resistance to disturbances and how acclimatization increases the ability of corals to resist future stress. Most...     

Influence of water flow on skeletal isotopic composition in the coral Pocillopora damicornis

Fragments of branching Pocillopora damicornis coral colonies were grown in experimental flumes under two water flow regimes. Colony size and buoyant weight increased most rapidly in the fast-flow regime. Branch tips from the upper and outer parts of the colonies showed the lowest and most consistent skeletal oxygen isotope ratios. Flow regime had little influence on the lowest oxygen isotope ratios, which were at least 3.5‰ lighter than the calculated oxygen isotopic equilibrium. These “kinetic” isotope effects are comparable to those observed in Porites corals. Relatively more branch tips showed extreme ¹⁸O depletions under low-flow conditions, and among small coral colonies. Isotopic variability was greater among branch tips from the lower and inner parts of the colonies and at high flow. Skeletal oxygen and carbon isotope ratios generally showed positive correlations. Despite the particularly large offsets from isotopic equilibrium, the isotopically lightest branches showed the greatest isotopic consistency and therefore would make the best isotopic thermometers. Isotopic variability within the colony may provide an indication of flow regime.     

Seasonal calcification of the coral Acropora digitifera from a subtropical marginal Okinawa reef under ocean acidification

Coral Reefs - Coral calcification is affected by the decrease in aragonite saturation state (Ωarag) caused by ocean acidification (OA). However, OA effects are modulated by other environmental...     

Ocean acidification partially mitigates the negative effects of warming on the recruitment of the coral,Orbicella faveolata

Coral Reefs - Ocean acidification and ocean warming constitute major threats to many calcifying reef organisms, including scleractinian corals. The combined effects of these two environmental...     

Study on the effects of near-future ocean acidification on marine yeasts: a microcosm approach

Marine yeasts play an important role in biodegradation and nutrient cycling and are often associated with marine flora and fauna. They show maximum growth at pH levels lower than present-day seawater pH. Thus, contrary to many other marine organisms, they may actually profit from ocean acidification. Hence, we conducted a microcosm study, incubating natural seawater from the North Sea at present-day pH (8.10) and two near-future pH levels (7.81 and 7.67). Yeasts were isolated from the initial seawater sample and after 2 and 4 weeks of incubation. Isolates were classified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and representative isolates were identified by partial sequencing of the large subunit rRNA gene. From the initial seawater sample, we predominantly isolated a yeast-like filamentous fungus related to Aureobasidium pullulans, Cryptococcus sp., Candida sake, and various cold-adapted yeasts. After incubation, we found more different yeast species at near-future pH levels than at present-day pH. Yeasts reacting to low pH were related to Leucosporidium scottii, Rhodotorula mucilaginosa, Cryptococcus sp., and Debaryomyces hansenii. Our results suggest that these yeasts will benefit from seawater pH reductions and give a first indication that the importance of yeasts will increase in a more acidic ocean.     

Impacts of elevated temperature and pCO2 on the brooded larvae of Pocillopora damicornis from Luhuitou Reef,China: evidence for local acclimatization

Coral Reefs - In this study, we tested whether larvae brooded by the reef coral Pocillopora damicornis from a naturally extreme and highly variable environment are preadapted to cope with predicted...     

Metabolomic signatures of increases in temperature and ocean acidification from the reef-building coral, <Emphasis Type="Italic">Pocillopora damicornis</Emphasis>

Introduction

As a changing climate threatens the persistence of terrestrial and marine ecosystems by altering community composition and function, differential performance of taxa highlights the need for predictive metrics and mechanistic understanding of the factors underlying positive performance in the face of environmental disturbances. Biochemical reactions within cells provide a snapshot of molecular regulation and flexibility during exposure to environmental stressors. However, because the organism is the unit of selection there is a need for the integration of metabolite data with organism physiology to understand mechanisms responsible for individual success under a changing climate.

Objectives

Our study aims to characterize the molecular response of reef corals to simulated global climate change stressors. Furthermore, we seek to relate changes in the molecular physiology to observations in overall colony response.

Methods

To this end, we applied a non-targeted metabolomic approach to describe lipid and primary metabolite composition after exposure of the reef-building coral Pocillopora damicornis to ambient and elevated experimental climate change conditions. We compared these metabolite data to organism physiology, specifically the key processes of photosynthesis, respiration, and calcification.

Results

Corals significantly altered their lipid and primary metabolite profiles in response to experimental treatments. Primary metabolite profiles predicted organisms’ net photosynthesis, but not calcification or respiration measures. Despite challenges in metabolome annotation, our data indicated corals alter carbohydrate composition, cell structural lipids, and signaling compounds in response to elevated treatment conditions.

Conclusions

The integration of metabolite and physiological data highlights the predictive power of metabolomics in defining organism performance and provides biomarkers for future studies. Here, we present a multivariate biomarker approach to assess climate change impacts and advance our mechanistic understanding of stress response in this keystone species.

     

Individual and interactive effects of ocean acidification,global warming,and UV radiation on phytoplankton

Rising carbon dioxide (CO₂) concentrations in the atmosphere result in increasing global temperatures and ocean warming (OW). Concomitantly, dissolution of anthropogenic CO₂ declines seawater pH, resulting in ocean acidification (OA) and altering marine chemical environments. The marine biological carbon pump driven by marine photosynthesis plays an important role for oceanic carbon sinks. Therefore, how ocean climate changes affect the amount of carbon fixation by primary producers is closely related to future ocean carbon uptake. OA may upregulate metabolic pathways in phytoplankton, such as upregulating ß-oxidation and the tricarboxylic acid cycle, resulting in increased accumulation of toxic phenolic compounds. Ocean warming decreases global phytoplankton productivity; however, regionally, it may stimulate primary productivity and change phytoplankton community composition, due to different physical and chemical environmental requirements of species. It is still controversial how OA and OW interactively affect marine carbon fixation by photosynthetic organisms. OA impairs the process of calcification in calcifying phytoplankton and aggravate ultraviolet (UV)-induced harms to the cells. Increasing temperatures enhance the activity of cellular repair mechanisms, which mitigates UV-induced damage. The effects of OA, warming, enhanced exposure to UV-B as well as the interactions of these environmental stress factors on phytoplankton productivity and community composition, are discussed in this review.     

Asexual reproduction does not produce clonal populations of the brooding coral Pocillopora damicornis on the Great Barrier Reef, Australia

We have investigated the relationship between genotypic diversity, the mode of production of brooded larvae and disturbance in a range of reef habitats, in order to resolve the disparity between the reproductive mode and population structure reported for the brooding coral Pocillopora damicornis. Within 14 sites across six habitats, the ratio of the observed (G _o) to the expected (G _e) genotypic diversity ranged from 69 to 100% of that expected for random mating. At three other sites in two habitats the G _o /G _e ranged from 35 to 53%. Two of these sites were recently bleached, suggesting that asexual recruitment may be favoured after disturbance. Nevertheless, our data suggest that brooded larvae, from each of five habitats surveyed, were asexually produced. While clonal recruitment may be important in disturbed habitats, the lack of clonality detected, both in this and earlier surveys of 40 other sites, implies that a disturbance is normally insufficient to explain this species’ continued investment in clonal reproduction.     

Ecological effects of ocean acidification and habitat complexity on reef-associated macroinvertebrate communities

The ecological effects of ocean acidification (OA) from rising atmospheric carbon dioxide (CO₂) on benthic marine communities are largely unknown. We investigated in situ the consequences of long-term exposure to high CO₂ on coral-reef-associated macroinvertebrate communities around three shallow volcanic CO₂ seeps in Papua New Guinea. The densities of many groups and the number of taxa (classes and phyla) of macroinvertebrates were significantly reduced at elevated CO₂ (425–1100 µatm) compared with control sites. However, sensitivities of some groups, including decapod crustaceans, ascidians and several echinoderms, contrasted with predictions of their physiological CO₂ tolerances derived from laboratory experiments. High CO₂ reduced the availability of structurally complex corals that are essential refugia for many reef-associated macroinvertebrates. This loss of habitat complexity was also associated with losses in many macroinvertebrate groups, especially predation-prone mobile taxa, including crustaceans and crinoids. The transition from living to dead coral as substratum and habitat further altered macroinvertebrate communities, with far more taxa losing than gaining in numbers. Our study shows that indirect ecological effects of OA (reduced habitat complexity) will complement its direct physiological effects and together with the loss of coral cover through climate change will severely affect macroinvertebrate communities in coral reefs.     

Two patterns of energy allocation for growth,reproduction and lipid storage in the scleractinian coral Pocillopora damicornis

A population of the coral Pocillopora damicornis was examined for 12 months to investigate whether different reproductive activities in the corals affected patcerns of energy allocation. Growth, the amount of lipid in the tissue, and reproductive activity were measured simultaneously at fortnightly intervals during the summer months when production of planulae was expected, and monthly for the cooler period of the year. Two group of corals could be identified: those which produced brooded larvae and formed ova and sperm during gametogenesis, and those which did not brood larvae and produced only sperm. Although they exhibited no morphological differences, these two groups displayed different patterns of energy allocation to growth, reproduction and lipid storage. Corals which did not produce brooded larvae grew one and a half times faster and had more lipid for storage after reproduction than those which produced brooded larvae. Corals that brooded larvae had more structural lipid before release of larvae than those without brooded larvae, reflecting a greater volume of reproductive material rich in lipid. These results demonstrate a substantial cost of reproduction since corals which did not produce brooded larvae and ova put more resources into grwoth and storage of lipid.     

Ocean temperature,but not acidification,causes sea anemone bleaching under a near-future climate scenario

Coral Reefs - Climate change is causing ocean temperature and partial pressure of carbon dioxide (pCO2) to increase. For sea anemones that have Symbiodiniaceae, high temperatures induce bleaching,...