Ask Vanessa: Our acidic oceans

Dear Vanessa,

I’m trying to learn more about climate change and have been reading as much as I can. I keep coming across terms I don’t understand, like ocean acidification. What is ocean acidification, and why does it matter?

- A curious reader

Dear Curious,

By now, most folks know that carbon dioxide-induced global warming is causing changes in ocean temperatures and precipitating a rise in sea levels. Still off the radar for many, though, is that carbon dioxide emissions are making the ocean more acidic. When carbon dioxide (CO2) is absorbed by seawater, carbonic acid is formed, reducing the water’s pH level and the concentration of carbonate ion. This process is commonly called ocean acidification. Perhaps surprisingly, ocean acidification is considered one of the most serious consequences of increased CO2 in the atmosphere.

It is estimated that the ocean has absorbed more than 528 billion tons of CO2 from the atmosphere – about one-third of human-caused carbon emissions – since the beginning of the industrial revolution.

On the one hand, the ocean’s absorption of CO2 helps reduce the amount of greenhouse gases in the atmosphere – a positive, useful function in these dire times. On the other hand, the ocean’s absorption of CO2 and the ensuing drop in seawater pH level has widespread and devastating effects on marine and human life. The lower pH level inhibits the ability of many marine plants and animals to build their shells and skeletal structure, in some cases even dissolving the shells. Ocean acidification is particularly harmful to surface and deep-water corals, plankton, snails, lobsters, clams, oysters and other mollusks.

From pristine reefs to coral wastelands

In Hawaii, climate change’s impact is raising alarms

The scientific projections are ominous.

If substantial steps aren’t taken globally to counter the effects of climate change, reefs in Hawai’i and around the world eventually could become coral wastelands, decimated by increasingly acidic and warming ocean waters.

Some scientists say such a scenario, which would wreak havoc with Hawai’i’s fisheries and the state economy, could come by the end of the century, perhaps even a few decades sooner.

But the projections are just those — projections.

Although they are based on computer models and reams of scientific data, much uncertainty remains.

No one knows, for instance, how a complex marine ecosystem, such as a reef in the middle of the Pacific, will be precisely affected by the increasing temperatures and higher levels of acidity brought on by the burning of fossil fuels.

One wild card is whether corals, resilient organisms that can rebound from some major stresses, will be able to adapt to climate change-related chemical alterations in the environment that are occurring at rates not seen for millions of years.

Scientists also are uncertain whether the predicted effects will happen as quickly or as severely as the models indicate.

“The thing to worry about is not that it will be as bad as we think,” said Paul Jokiel, researcher at the Hawai’i Institute of Marine Biology. “It’s that it will be much worse than we think.”

Synergistic interactions between stressors to coral reefs (session at the 15th Ocean Sciences Meeting, February 2010)

Session on Synergistic interactions between stressors to coral reefs at the 15th Ocean Sciences Meeting, which will be held 22-26 February, 2010, in Portland, Oregon. The theme of this meeting is, From Observation to Prediction in the 21st Century?. Please visit the conference website for more information.

Aim and Scope of this Session, IT04:

Over the past few decades coral reefs worldwide have degraded due to both natural and anthropogenic environmental factors. Natural variability in the ocean-atmosphere system (El Nino events, North Atlantic Oscillation) can cause large-scale changes in storm tracks, sea-surface height, water temperatures and rainfall. Recent IPCC projections suggest changes in air and sea surface temperature, precipitation, CO2, pH, and sea level all will significantly impact coral reef ecosystems. At the same time, human activities in the coastal zone (e.g. livestock grazing and coastal development) have increased the delivery of sediment, nutrients, and contaminants to coral reef ecosystems. Assessing how these ecosystems function and identifying the synergistic effects of local versus global stressors will help us to better manage them as a resource. This session focuses on advancements in understanding the natural environmental controls on coral reefs and how these processes have interacted with anthropogenic stressors to impact these fragile ecosystems.

Topics of interest include, but are not limited to, the influence of, and interaction between, changes in sea surface temperatures, pH, sea level, storms, waves, floods, sediment, nutrients, and contaminants on coral reefs. Summaries of current regional investigations, site- specific studies, and modeling results are all encouraged.

Morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater: Insights into the biomineralization response to ocean acidification

We reared primary polyps (new recruits) of the common Atlantic golf ball coral Favia fragum for 8 days at 25°C in seawater with aragonite saturation states ranging from ambient (Ω = 3.71) to strongly undersaturated (Ω = 0.22). Aragonite was accreted by all corals, even those reared in strongly undersaturated seawater. However, significant delays, in both the initiation of calcification and subsequent growth of the primary corallite, occurred in corals reared in treatment tanks relative to those grown at ambient conditions. In addition, we observed progressive changes in the size, shape, orientation, and composition of the aragonite crystals used to build the skeleton. With increasing acidification, densely packed bundles of fine aragonite needles gave way to a disordered aggregate of highly faceted rhombs. The Sr/Ca ratios of the crystals, measured by SIMS ion microprobe, increased by 13%, and Mg/Ca ratios decreased by 45%. By comparing these variations in elemental ratios with results from Rayleigh fractionation calculations, we show that the observed changes in crystal morphology and composition are consistent with a >80% decrease in the amount of aragonite precipitated by the corals from each “batch” of calcifying fluid. This suggests that the saturation state of fluid within the isolated calcifying compartment, while maintained by the coral at levels well above that of the external seawater, decreased systematically and significantly as the saturation state of the external seawater decreased. The inability of the corals in acidified treatments to achieve the levels of calcifying fluid supersaturation that drive rapid crystal growth could reflect a limit in the amount of energy available for the proton pumping required for calcification. If so, then the future impact of ocean acidification on tropical coral ecosystems may depend on the ability of individuals or species to overcome this limitation and achieve the levels of calcifying fluid supersaturation required to ensure rapid growth.

NSF Postdoctoral Scholar – Coral Ecophysiology

Application deadline: 1 September 2009
Start date: negotiable, 1 January 2010
Salary: $41,000

Applications are invited for a 3-year, NSF-funded postdoctoral scholar position at California State University, Northridge (CSUN), to complete research in the area of Global Climate Change (GCC) and its effects on coral larvae. The successful candidate will work closely with PJ Edmunds (grant PI, peter.edmunds@csun.edu) to elucidate the effects of rising temperature and ocean acidification on the physiology of larvae from brooding corals in Taiwan and Moorea. The research focuses on the ecophysiology of larvae under normal conditions, perturbations of these routine processes by global climate change effects, and the integration of results through dynamic energy budgets and other modeling approaches. Candidates are expected to have strong field-based experience with the ecophysiology of tropical reef corals and/or the biology/physiology of invertebrate larvae, and are expected to work overseas in Taiwan (3-4 mo/y) and Moorea (3 weeks/y). This position provides unique opportunities to work with a small team studying coral biology in the Caribbean and Pacific, to gain professional experience in a Pacific rim context, and work with colleagues at the National Museum of Marine Biology and Aquarium (Taiwan) and the Moorea Coral Reef LTER.