Archive for January 14th, 2013

The future of shelf ecosystems (PhD position)

Supervisors: Dr Daniela Schmidt, Dr Emily Rayfield and Prof Juliet Brodie (NHM London)

The ocean serves us in many ways, from regulating climate to providing food, livelihood and recreation. These services are increasingly impacted by a growing number of environmental stressors such as warming, acidification, and deoxygenation, and more locally fishing, trawling, eutrophication, and pollution (Turley et al., 2010). While previous work was able show that species can calcify even in a warmer more acidic ocean (Ragazzola et al., 2012) few have addressed the question if thinner, less dense skeletal structure will allow these organisms to fulfil their role in the marine ecosystem, provide habitats for other organisms and livelihoods for people.

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Disturbance effects to coral recruitment dynamics on the Great Barrier Reef

Coral recruitment represents a critical phase in the development of coral populations, important to the recovery of coral reefs affected by anthropogenic and natural disturbances. Successful recruitment is significant to the resilience of coral reefs, and degraded reefs often exhibit declining rates of coral recruitment through a poorly understood combination of reduced adult fecundity, decreased settlement, increased competition for space, and high rates of early mortality. The stages of successful recruitment are complex and, whilst evidence indicates that climate change disturbances can adversely reduce coral recruitment, empirical investigations into ecological interactions are limited.

The first section of this thesis used experimental manipulations to investigate how anthropogenic ocean acidification (OA) affects both pre- and post-settlement processes associated with coral recruitment. The first data chapter (Chp. 2) focussed on how OA altered the encrusting benthic community and its subsequent effects on coral settlement. Strikingly, the only preferred settlement substrate in the experimental controls (Titanoderma) was avoided by coral larvae as pCO2 increased, and other substrata were selected. Chapter 3 then used a series of laboratory settlement assays to isolate the effect of OA on the survival and settlement of coral larvae with three ecologically important species of crustose coralline algae (CCA). Here, with all CCA species, the rates of coral settlement declined as pCO2 increased, but the magnitude of this effect was highest with Titanoderma. The last experimental chapter (Chp. 4) tested whether the reduced growth of coral recruits caused by OA would increase their mortality by prolonging their vulnerability to an acute disturbance: fish herbivory on surrounding algal turf. Compared to ambient conditions, recruits needed to double their size at the highest pCO2 to escape incidental grazing mortality. This general trend was observed with three groups of predators (blenny, surgeonfish and parrotfish), and the magnitude of the effect was highest with parrotfish.

The final data chapter (Chp. 5) of this thesis used permanently marked benthic plots and settlement tiles in a disturbed reef flat and reef slope habitat to investigate how life-history and adult stock influenced early recovery dynamics over a three year period. The reef slope was characterised by higher amounts of available settlement substrata, more than twice the rates of coral recruitment, and significantly higher recruit survival compared to the reef flat. In both habitats, as adult coral populations increased, so too did the density of recruits, yielding a significant positive stock-recruitment relationship. This positive stock-recruitment relationship was confined to species that brood their larvae, while no relationship was found for spawning corals. However, the stock-recruitment function did not influence the early recovery in either habitat. Instead, it was the presence of particular fast-growing acroporids on the reef slope that drove the rapid increase in coral cover, demonstrating the importance of life-history traits in assessing coral assemblage recovery. Using population matrices, major recruitment bottlenecks were determined for coral taxa common to Indo-Pacific reefs.

This thesis has captured some of the effects of both natural and anthropogenic disturbances on processes intrinsic to coral recruitment ecology. Of particular importance are the documented interactions among different biological groups – i.e. corals, algae, and herbivores – influenced by different kinds of stressors – e.g. ocean acidification, competition, and herbivory. Benthic communities often respond to perturbations in complex and unpredictable ways, so increasing our understanding of how recruiting corals respond to acute and chronic disturbances assists in the predictive modelling of benthic communities to make better informed management decisions.

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Interactive effects of elevated temperature and CO2 levels on metabolism and oxidative stress in two common marine bivalves (Crassostrea virginica and Mercenaria mercenaria)

Marine bivalves such as the hard shell clams Mercenaria mercenaria and eastern oysters Crassostrea virginica are affected by multiple stressors, including fluctuations in temperature and CO2 levels in estuaries, and these stresses are expected to be exacerbated by ongoing global climate change. Hypercapnia (elevated CO2 levels) and temperature stress can affect survival, growth and development of marine bivalves, but the cellular mechanisms of these effects are not yet fully understood. In this study, we investigated whether oxidative stress is implicated in cellular responses to elevated temperature and CO2 levels in marine bivalves. We measured the whole-organism standard metabolic rate (SMR), total antioxidant capacity (TAOC), and levels of oxidative stress biomarkers in the muscle tissues of clams and oysters exposed to different temperatures (22 and 27 °C) and CO2 levels (the present day conditions of ~ 400 ppm CO2 and 800 ppm CO2 predicted by a consensus business-as-usual IPCC emission scenario for the year 2100). SMR was significantly higher and the antioxidant capacity was lower in oysters than in clams. Aerobic metabolism was largely temperature-independent in these two species in the studied temperature range (22–27 °C). However, the combined exposure to elevated temperature and hypercapnia led to elevated SMR in clams indicating elevated costs of basal maintenance. No persistent oxidative stress signal (measured by the levels of protein carbonyls, and protein conjugates with malondialdehyde and 4-hydroxynonenal) was observed during the long-term exposure to moderate warming (+ 5 °C) and hypercapnia (~ 800 ppm CO2). This indicates that long-term exposure to moderately elevated CO2 and temperature minimally affects the cellular redox status in these bivalve species and that the earlier observed negative physiological effects of elevated CO2 and temperature must be explained by other cellular mechanisms.

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Effects of feeding and light intensity on the response of the coral Porites rus to ocean acidification

Recently, it has been suggested that there are conditions under which some coral species appear to be resistant to the effects of ocean acidification. To test if such resistance can be explained by environmental factors such as light and food availability, the present study investigated the effect of 3 feeding regimes crossed with 2 light levels on the response of the coral Porites rus to 2 levels of pCO2 at 28 °C. After 1, 2, and 3 weeks of incubation under experimental conditions, none of the factors—including pCO2—significantly affected area-normalized calcification and biomass-normalized calcification. Biomass also was unaffected during the first 2 weeks, but after 3 weeks, corals that were fed had more biomass per unit area than starved corals. These results suggest that P. rus is resistant to short-term exposure to high pCO2, regardless of food availability and light intensity. P. rus might therefore represent a model system for exploring the genetic basis of tolerance to OA.

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Diurnal changes in seawater carbonate chemistry speciation at increasing atmospheric carbon dioxide

Natural variability in seawater pH and associated carbonate chemistry parameters is in part driven by biological activities such as photosynthesis and respiration. The amplitude of these variations is expected to increase with increasing seawater carbon dioxide (CO2) concentrations in the future, because of simultaneously decreasing buffer capacity. Here, we address this experimentally during a diurnal cycle in a mesocosm CO2 perturbation study. We show that for about the same amount of dissolved inorganic carbon (DIC) utilized in net community production diel variability in proton (H+) and CO2 concentrations was almost three times higher at CO2 levels of about 675 ± 65 in comparison with levels of 310 ± 30 μatm. With a simple model, adequately simulating our measurements, we visualize carbonate chemistry variability expected for different oceanic regions with relatively low or high net community production. Since enhanced diurnal variability in CO2 and proton concentration may require stronger cellular regulation in phytoplankton to maintain respective gradients, the ability to adjust may differ between communities adapted to low in comparison with high natural variability.

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Effective practices for communicating ocean acidification – workshop summary

After the September “Oceans in a High-CO2 World” Meeting in Monterey, CA, the NOAA West Coast National Marine Sanctuaries hosted a workshop titled “Effective Practices for Communicating Ocean Acidification.”  This workshop brought together scientists, educators, and communications experts from federal agencies, academia and research, aquariums and museums, environmental non-governmental organizations (NGOs), and other organizations to discuss key messages, tools, and case studies to use when educating the public about OA.

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Spatiotemporal variability and long-term trends of ocean acidification in the California Current System (update)

Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS) have a naturally low pH and aragonite saturation state (Ωarag), making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS) to conduct preindustrial and transient (1995–2050) simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric pCO2 and increasing oceanic dissolved inorganic carbon concentrations at the lateral boundaries, as projected by the NCAR CSM 1.4 model for the IPCC SRES A2 scenario. Our results show a large seasonal variability in pH (range of ~ 0.14) and Ωarag (~ 0.2) for the nearshore areas (50 km from shore). This variability is created by the interplay of physical and biogeochemical processes. Despite this large variability, we find that present-day pH and Ωarag have already moved outside of their simulated preindustrial variability envelopes (defined by ±1 temporal standard deviation) due to the rapidly increasing concentrations of atmospheric CO2. The nearshore surface pH of the northern and central CCS are simulated to move outside of their present-day variability envelopes by the mid-2040s and late 2030s, respectively. This transition may occur even earlier for nearshore surface Ωarag, which is projected to depart from its present-day variability envelope by the early- to mid-2030s. The aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m within the next 25 yr, causing near-permanent undersaturation in subsurface waters. Due to the model’s overestimation of Ωarag, this transition may occur even earlier than simulated by the model. Overall, our study shows that the CCS joins the Arctic and Southern oceans as one of only a few known ocean regions presently approaching the dual threshold of widespread and near-permanent undersaturation with respect to aragonite and a departure from its variability envelope. In these regions, organisms may be forced to rapidly adjust to conditions that are both inherently chemically challenging and also substantially different from past conditions.

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L’acidification des océans (video; in French)

Découvrez une nouvelle compréhension de l’acidification des océans, un phénomène issu d’un échange de dioxyde de carbone entre l’atmosphère et l’océan. Cela provoque une diminution du pH de l’eau de mer et met en danger certaines espèces.

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Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels of atmospheric carbon dioxide (update)

Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO2), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO2 perturbation study in Kongsfjorden on the west coast of Spitsbergen (Norway), in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO2 levels ranging initially from about 185 to 1420 μatm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll a standing stocks (Chl a), peaked three times in all mesocosms. However, while absolute Chl a concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured as high in comparison to low CO2 during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO2 effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO2 effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO2-related shifts in nutrient flow into different phytoplankton groups (mainly dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO2.

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Dickson Prize: Ocean acidification – causes, time scales and consequences

Monday 4 March 2013, 4:30 pm, McConomy Auditorium, First Floor, University Center

Honoring François M.M. Morel, Albert G. Blanke Professor of Geosciences, Princeton University

The dissolution of anthropogenic carbon dioxide into the ocean causes the water to become more acidic, leading to a variety of direct and indirect effects on the chemistry of surface seawater and the physiology of its inhabitants. How this ocean acidification, which has been called “global warming’s evil twin” will affect marine ecosystems is a topic of active research and much debate. Some predict wholesale changes in primary production, crashes in fisheries stocks, and the disappearance of coral reefs. Others believe that marine ecosystems will adapt and that no major effects should be expected. What makes such predictions particularly difficult is the century time scale of ocean acidification, much longer than the laboratory or field experiments we can carry out, and much shorter than the resolution of our geological records for similar events in the Earth’s distant past. Our best hope to assess the likely consequences of ocean acidification rests with a mechanistic approach in which the physiological and biochemical effects of the predictable changes in chemistry are studied at the molecular level. This will be exemplified by a series of examples in which we examine the consequences of increasing the CO2 concentration and decreasing the pH on key processes such as photosynthesis, the precipitation of calcium carbonate, and the fixation of atmospheric nitrogen.

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Ocean acidification: understanding changing chemistry in Alaska coastal waters

Project Status: This project began in January, 2010 and was completed in December, 2012

Ocean acidification is a problem created by the increasing levels of carbon dioxide in our atmosphere, and it is harmful to certain plankton, shellfish, coral, and marine plants. We have begun a pilot study in Kachemak Bay, Alaska, to measure the variations in acidity that result from freshwater input from glaciers, snowmelt, and rainfall and from upwelling ocean water. The bay’s unique geographic features provide a cost-effective way to study varying acidity levels.

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Antarctic science: Professor Brownlee joins the Antarctic Ocean Acidification cruise

Director of the MBA Colin Brownlee joins the UK Ocean Acidification Research Programme cruise on the James Clark Ross in the Southern Ocean this week. The UK Ocean Acidification Research Programme (UKOARP) is looking at planktonic and microbial ecosystems in high latitudes, particularly in the context of ocean acidification. Scientists on the cruise will be examining the effects of increasing Carbon dioxide (CO2) on marine ecosystems.

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Ocean acidification seminar scheduled for Everett

EVERETT — Snohomish County residents wanting to learn more about ocean acidification are invited to a free seminar Jan. 24 at the Everett Station.

The event, hosted by the Snohomish County Marine Resources Committee (MRC), will feature presentations by three members of the Washington State Panel on Ocean Acidification. The seminar is scheduled for 6 to 8 p.m. in the Weyerhaeuser Room at Everett Station, 3201 Smith Ave., Everett.

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Ocean acidification upsets the acid-base balance of corals

Researchers in Monaco and Australia have solved a key part of the mystery surrounding why ocean acidification slows down the growth of reef-building corals.

Ocean acidification, caused by seawater uptake of man-made carbon dioxide, is rapidly changing the chemistry of the world’s oceans, and current evidence suggests that ocean acidification will be a big threat to marine life in the future, particularly corals that form the structural base of vibrant reef ecosystems.

But what has always remained unclear is how and why ocean acidification is such a problem for corals.

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New thematic series – ‘Ocean acidification: approaches to mitigation and adaptation’

A new thematic series- ‘Ocean acidification: approaches to mitigation and adaptation’ is to be published in Carbon Balance and Management. This series aims to provide a widely accessible forum for the presentation and discussion of research into ocean acidification, and how these studies can be used to inform management and policy.

In this series, we not only aim to highlight important findings in this area, but also to facilitate interdisciplinary discussions with the overriding goal of working towards a comprehensive global carbon strategy. Continued study and assessment of oceanic carbon is key to enhancing our understanding of the global carbon cycle, and the intention of this series is to highlight this importance of research in this area.

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