Archive for July, 2009

Effects of ocean acidification over the life history of the barnacle Amphibalanus amphitrite

Increased levels of atmospheric CO2 are anticipated to cause decreased seawater pH. Despite the fact that calcified marine invertebrates are particularly susceptible to acidification, barnacles have received little attention. We examined larval condition, cyprid size, cyprid attachment and metamorphosis, juvenile to adult growth, shell calcium carbonate content, and shell resistance to dislodgement and penetration in the barnacle Amphibalanus amphitrite reared from nauplii in either ambient pH 8.2 seawater or under CO2-driven acidification of seawater down to a pH of 7.4. There were no effects of reduced pH on larval condition, cyprid size, cyprid attachment and metamorphosis, juvenile to adult growth, or egg production. Nonetheless, barnacles exposed to pH 7.4 seawater displayed a trend of larger basal shell diameters during growth, suggestive of compensatory calcification. Furthermore, greater force was required to cause shell breakage of adults raised at pH 7.4, indicating that the lower, active growth regions of the wall shells had become more heavily calcified. Ash contents (predominately calcium carbonate) of basal shell plates confirmed that increased calcification had occurred in shells of individuals reared at pH 7.4. Despite enhanced calcification, penetrometry revealed that the central shell wall plates required significantly less force to penetrate than those of individuals raised at pH 8.2. Thus, dissolution rapidly weakens wall shells as they grow. The ramifications of our observations at the population level are important, as barnacles with weakened wall shells are more vulnerable to predators.
Continue reading ‘Effects of ocean acidification over the life history of the barnacle Amphibalanus amphitrite’

Oceans becoming more acidic, endangering sea life

Rising levels of carbon dioxide in the atmosphere are a major contributor to climate change, and now a new study has confirmed that atmospheric CO2 is also affecting the ocean chemistry, potentially threatening marine life.

Montana State University scientist Robert Dore has been taking samples of water in the Pacific Ocean for almost two decades.

“We’re sailing out of Honolulu harbor. We’re in the harbor right now and just about to break away from the dock.”

I reached Prof. Dore on board the research vessel Kilo Moana, about to leave for a point in the Pacific known as Station Aloha, where he has been studying the ocean water since the late 1980s.

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Ocean exploration as vital as our reach into outer space

When the lunar module Eagle landed on the moon 40 years ago, I was in Denver with my five sisters, mom and dad watching the blurry, ghostly images of Neil Armstrong and Buzz Aldrin tentatively walk on a barren sea called Tranquility. The excitement in our living room was palpable. The seemingly impossible goal that President Kennedy charted out eight years before had just happened. I felt emboldened, empowered and infused with the notion that anything is possible.

The previous summer I experienced my own exploration awakening, having the opportunity to study invertebrates at the Marine Biological Laboratory in Woods Hole, Mass. As a Colorado native, I was astounded to discover a wealth of life in oceans. It was a world filled with incredible diversity of forms and functions, from seastars to lobsters to exotic small creatures, many of whose daily rhythms were profoundly linked to the far away moon and its influence on the Earth’s tides.

The Apollo triumph had an unexpected impact on how we view our oceans. It energized a new focus on the vast unexplored regions of our own home planet. And through iconic images like the Apollo 8 “Earthrise photo,” an entire generation was inspired to cherish and protect our planetary home, which from the perspective of space is an ocean-dominated world.

Last month, a government report detailed the danger that climate change poses to oceans and coastal areas. Ocean acidification, resulting from the uptake of carbon dioxide by ocean waters, is harming corals, shellfish, and other creatures. Warmer ocean waters are stressing corals, causing systems to move to new places and enhancing diseases. Climate change is leading to greater coastal erosion and stronger storm surges. These changes complicate efforts to protect oceans and coasts already under heavy stress from pollution, overfishing and habitat destruction.

Continue reading ‘Ocean exploration as vital as our reach into outer space’

A changing ocean seen with clarity

The Hawaiian archipelago, the most remote group of islands on Earth, has long been associated with the world’s most recognizable image of global change. The Mauna Loa atmospheric CO2 record, begun in March 1958 by Charles David Keeling, shows with startling clarity the saw-tooth pattern of the seasonal changes of land vegetation, and the still astonishing, dominating, rise forced by fossil fuel burning which is rapidly changing our world. Within perhaps only 5 years the peak in the annual signal atop Mauna Loa will touch the 400 ppm by volume mark, which would have been inconceivable to scientists of the first half of the twentieth century. But there is one huge and environmentally critical signal that is not easily seen in the “Keeling curve,” and that is the oceanic uptake of fossil fuel CO2. In this issue of PNAS, Dore et al. (1) document with great clarity the changes in ocean CO2 chemistry and pH occurring in the ocean in the waters off Hawaii from fossil fuel CO2 invasion.

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The interaction of ocean acidification and carbonate chemistry on coral reef calcification: evaluating the carbonate chemistry Coral Reef Ecosystem Feedback (CREF) hypothesis on the Bermuda coral reef

Despite the potential impact of ocean acidification on ecosystems such as coral reefs, surprisingly, there is very limited field data on the relationships between calcification and carbonate chemistry. In this study, contemporaneous in situ datasets of carbonate chemistry and calcification rates from the high-latitude coral reef of Bermuda over annual timescales provide a framework for investigating the present and future potential impact of rising pCO2 and ocean acidification on coral reef ecosystems in their natural environment. A strong correlation was found between the in situ rates of calcification for the major framework building coral species Diploria labyrinthiformis and the seasonal variability of [CO32-] and Ωaragonite, rather than other environmental factors such as light and temperature. These field observations also provide sufficient data to hypothesize that there is a seasonal “Carbonate Chemistry Coral Reef Ecosystem Feedback” (CREF hypothesis) between the primary components of the reef ecosystem (i.e. scleractinian hard corals and macroalgae) and carbonate chemistry. In early summer, strong net autotrophy from benthic components of the reef system enhance [CO32-] and Ωaragonite conditions, and rates of coral calcification due to the photosynthetic uptake of CO2. In late summer, rates of coral calcification are suppressed by release of CO2 from reef metabolism during a period of strong net heterotrophy. It is likely that this seasonal CREF mechanism is present in other tropical reefs although attenuated compared to high-latitude reefs such as Bermuda. Due to lower annual mean surface seawater [CO32-] and Ωaragonite in Bermuda compared to tropical regions, we anticipate that Bermuda corals will experiences seasonal periods of zero net calcification within the next decade at [CO32-] and Ωaragonite thresholds of ~184 mmoles kg−1 and 2.65. The Bermuda coral reef is one of the first responders to the negative impacts of ocean acidification, and we estimate that calcification rates for D. labyrinthiformis have declined by >50% compared to pre-industrial times.

Continue reading ‘The interaction of ocean acidification and carbonate chemistry on coral reef calcification: evaluating the carbonate chemistry Coral Reef Ecosystem Feedback (CREF) hypothesis on the Bermuda coral reef’

Experimental studies of ocean-acidification impacts on Mediterranean seafood species

An experimental facility has been established at the IAEA Radioecology Laboratory to study the effects of ocean acidification (OA) on various marine organisms, particularly from the Mediterranean Sea. Relative to other research groups that are studying OA, our focus is on commercially valuable seafood, beginning with fishes and cephalopods, and not on the ‘mega- calcifiers’ with shells of calcium carbonate. Thus these seafood taxa are not chosen based on ana priori mechanistic hypothesis of thermodynamic control of CaCO3 precipitation and dissolution. We have used a suite of radiotracers to assess short-term rates of incorporation of essential elements such as Ca and Zn, and trace contaminants that are also expected to increase in the future with industrial growth and increased nuclear power production to mitigate carbon emissions (GESAMP, 2001; IAEA, 2008). Our first results indicate morphological and/or physiological impacts of ocean acidification (OA) among these two commercially important taxa. Thus direct impacts of ocean acidification appear to extend beyond the marine calcifiers.

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Effect of elevated pCO2 on the boron isotopic composition into the Mediterranean scleractinian coral Cladocora caespitosa

The Intergovernmental Panel on Climate Change (IPCC) predicts atmospheric CO2 partial pressure (pCO2) ranging from 490 to 1,250 ppm in 2100, depending on the socio-economic scenario
considered (Prentice et al., 2001). Because one third of anthropogenic CO2 emissions has been stored in the oceans, ocean pH has already declined by 0.1 unit compared with preindustrial values (Orr et al., 2005) and is predicted to decrease by another 0.4 unit by the end of the century (Caldeira and Wickett, 2003). Seawater acidification will lead to a shift in inorganic carbon equilibria towards higher CO2and lower carbonate ion concentrations.

Continue reading ‘Effect of elevated pCO2 on the boron isotopic composition into the Mediterranean scleractinian coral Cladocora caespitosa’

Impact of acidification on pelagic calcifying organisms in the Mediterranean Sea

The carbonate system of the Mediterranean Sea and the response of the highly adapted organisms to the rapid CO2 increase are both poorly understood. Coccolithophores (planktonic photoautotrophic microalgae) are the dominant calcifying organisms in the Mediterranean today. Their calcite plates (coccoliths) present a large variability in both size and carbonate mass. Generally, supersaturation with respect to calcite and aragonite is observed throughout the entire Basin, which may be one of the reasons for overcalcification observed in coccolithophores in the eastern Mediterranean surface sediments. At the same time, however, effects that are ascribed to drastic increase in anthropogenic CO2 and subsequently in surface water acidification can be possibly observed in the coccolith morphology in other parts of the Mediterranean.

Continue reading ‘Impact of acidification on pelagic calcifying organisms in the Mediterranean Sea’

Ocean acidification and its impact on the early life-history stages of marine animals

The world’s oceans are slowly becoming more acidic and profound changes in marine ecosystems are certain. Expected changes for the coming century will have significant affects on marine animals, especially those lacking adequate physiological buffering capacity and/or with calcareous skeletons such as echinoderms. In addition, alarmingly little is known about the long term impact of predicted pH changes on marine invertebrate larval development. Data currently available shows that the impact of ocean acidification (OA) on marine animals is not easy to predict (e.g. calcareous v.s. non-calcareous species, negative v.s. positive effects), furthermore it is species-specific even within closely related taxa and operates in synergy with other environmental parameters (e.g. temperature, food availability). An holistic approach on several generations including all phases of individual life cycles is required and essential. Further studies should focus on an established and robust frame of reference for life-history analyses, including temporal as well as developmental stages. Moreover, it is important to work in realistic abiotic (e.g. pH, temperature) and biotic (e.g. nutrient/food concentration) conditions, for example within a range of seawater pH predicted to occur by the year 2100 (?pH ≈- 0.2 to – 0.4 units) regulated by manipulation of environmental CO2 levels. Our view is that we need studies that embrace a wide range of carefully selected taxa and that also include careful consideration of life-history strategies exhibited by marine organisms. These considerations are illustrated by examples from our own research.

Continue reading ‘Ocean acidification and its impact on the early life-history stages of marine animals’

Impact of ocean acidification on marine shellfish

Ocean acidification resulting from human emissions of carbon dioxide has already lowered and will further lower surface ocean pH. The consequent decrease in calcium carbonate saturation potentially threatens calcareous marine organisms. Among these organisms, shellfish are very important species of a great ecological and also economical value. This paper reviews several reportson the effects of acidification on mollusc species. While numerous studies have shown a significant impact of decreasing seawater pH on shellfish growth and health, most of these studies considered a decrease in pH much higher than the one projected for the end of the century (-0.4 unit). Within this range (8.1-7.7), it appears that acidification does not have a dramatic effect on these species at least over few weeks exposure. However, several studies showed an alteration of metabolic rates and health of these organisms which could be related to shell dissolution and could cause significant loss over longer time-scales. It is therefore of utmost importance to carefully assess the relationship between shellfish calcification/dissolution rates and seawater saturation state with respect to calcium carbonate.

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Ocean acidification in the IPCC AR5 WG II

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