Global warming turning sea into acid bath

Mark Henderson, The Times 9 Jun 08;

Increasing carbon dioxide emissions could leave species such as coral and sea urchins struggling to survive by the end of the century because they are making the oceans more acidic, research led by British scientists suggests.

The study of how acidification affects marine ecosystems has revealed a striking impact on animal and plant life. The findings, from a team led by Jason Hall-Spencer, of the University of Plymouth, indicate that rising carbon emissions will alter the biodiversity of the seas profoundly, even before the effects of global warming are taken into account.

Greater concentrations of carbon dioxide in the atmosphere mean that more of the gas becomes dissolved in seawater, increasing its acidity. This will have good consequences for some species, but be catastrophic for others.

Dr Hall-Spencer's team investigated the likely effects of acidification by studying natural underwater vents off the coast of Italy, where carbon dioxide bubbles up through the sea floor. This makes the water around the vents significantly more acidic than it is in surrounding areas.

The study, published in the journal Nature, shows that certain species are very badly affected by rising acidity. Corals of the Caryophyllia, Cladocora and Balanophyllia varieties, for example, were common in on the sea bed in the region, but absent close to the vents. Sea urchins and sea snails were also affected badly by the high acidity.

Other species, including sea-grass and a type of algae known as Sargassum, thrived as the extra carbon dioxide has a fertilising effect. This extra growth, however, can be damaging to other sea life - Sargassum is an alien invasive species, carried to the region in the ballast of shipping.

The research team is the first to use natural underwater carbon dioxide vents to assess how acidity caused by the gas influences sea life. “Our field studies provide a window on the future of the oceans in a high CO2 world,” Dr Hall-Spencer said.

“We show the dramatic ecological consequences of ocean acidification including the removal of corals, snails and sea urchins and the proliferation of invasive alien algae.

“Our observations verify concerns, based on laboratory experiments and model predictions, that marine food webs will be severely disrupted and major ecological tipping-points are likely if human CO2 emissions continue unabated.”

This appraisal of life in a more acidic ocean was if anything conservative, Dr Hall-Spencer said, because it mimicked future ecosystems only partially.

The acidity around carbon dioxide vents can be reduced by rough conditions, which dilute the water - something that would not happen if the whole ocean was highly acidic.

The researchers also noted that while fish continued to swim through more acidic waters, they avoided breeding or spawning in them. “That isn't a problem at the moment, as they can go elsewhere,” Dr Hall-Spencer said. “But in a more acidic ocean there will be no escape.”

Global warming will also have an independent impact on sea life, by raising ocean temperatures.

Marine life is destroyed by acid environment
Paul Eccleston, The Telegraph 8 Jun 08;

Traditional marine communities containing creatures such as sea urchins and snails are being destroyed as CO2 emissions make their environment more acidic.

Algae which is vital for the well-being of coral reefs is also retreating as acidity increases and is being replaced by invasive species which don't offer coral the same protection.

The changes have been witnessed for the first time by a British-led team monitoring volcanic carbon dioxide vents off the Italian coast in the Mediterranean.

Until now marine scientists have only been able to use laboratory experiments and modelling techniques to predict what the possible consequences of increased CO2 levels for marine life will be.

But observations by the international team led by Royal Society University Research Fellow Jason Hall-Spencer at the University of Plymouth have confirmed fears that entire ecosystems face possibly catastrophic change.

Dr Hall-Spencer said; "Nobody has looked at the biological effects of ocean acidification on this scale before.

Previous studies have been small scale, short-term and laboratory-based, so it has been very difficult to predict the wider effects of increasing CO2 emissions on marine life. We show how whole marine communities and ecosystems change due to the long-term effects of acidification."

CO2 levels are expected to be double that of pre-industrial levels by 2100 and will be considerably higher than at any time for millions of years.

The world's oceans are the principal sink for man-made CO2 which is estimated to have caused a 30% increase in the concentration of hydrogen in surface waters since the early 1900s and making sea water more acidic.

Working in the Mediterranean the team found different gradients of acidity caused by gases emerging from the volcanic vents which allowed them to use it as a 'time tunnel' and to look at the type of conditions expected in our oceans in 2020, 2050, 2100 and beyond.

Concentrating on the levels of acidity expected by the end of the century they found that key marine group such as coral, coralline algae and sea urchins die out. They are replaced by groups more tolerant of acidic waters such as brown seaweed and seagrasses.

Because these species are common in oceans and seas across the globe the changes are a clear indicator that biodiversity will decrease dramatically worldwide.

Dr Hall-Spencer said: "What we saw was very dramatic and shocking.

"All the predictions made in lab experiments about acidity causing the disappearance of species is coming true.

"When we looked in the field it was already happening.

I must admit I though a lot of the claims being made about species disappearing amounted to scaremongering but now I have seen it with my own eyes.

"Our field studies provide a window on the future of the oceans in a high CO2 world. We show the dramatic ecological consequences of ocean acidification including the removal of corals, snails and sea urchins and the proliferation of invasive alien algae."

"Our observations verify concerns, based on laboratory experiments and model predictions, that marine food webs will be severely disrupted and major ecological tipping points are likely if human CO2 emissions continue unabated."

Natural lab shows sea's acid path
Richard Black, BBC News 8 Jun 08;

Natural carbon dioxide vents on the sea floor are showing scientists how carbon emissions will affect marine life.

Dissolved CO2 makes water more acidic, and around the vents, researchers saw a fall in species numbers, and snails with their shells disintegrating.

Writing in the journal Nature, the UK scientists suggest these impacts are likely to be seen across the world as CO2 levels rise in the atmosphere.

Some of the extra CO2 emitted enters the oceans, acidifying waters globally.

Studies show that the seas have become more acidic since the industrial revolution.

Research leader Jason Hall-Spencer from the University of Plymouth said that atmospheric CO2 concentrations were now so high that even a sharp fall in emissions would not prevent some further acidification.

"It's clear that marine food webs as we know them are going to alter, and biodiversity will decrease," he told BBC News.

"Those impacts are inevitable because acidification is inevitable - we've started it, and we can't stop it."

Natural lab

Corals construct their external skeletons by extracting dissolved calcium carbonate from seawater and using it to form two minerals, calcite and aragonite. Molluscs use the same process to make their shells.

As water becomes more acidic, the concentration of calcium carbonate falls. Eventually there is so little that shells or skeletons cannot form.

Around the vents which Dr Hall-Spencer's team investigated, in the Mediterranean Sea near the Italian coast, CO2 bubbling into the water forms a sort of natural laboratory for studying the impacts of acidified water on marine life.

Globally, the seas now have an average pH of about 8.1 - down about 0.1 since the dawn of the industrial age.

Around the vents, it fell as low as 7.4 in some places. But even at 7.8 to 7.9, the number of species present was 30% down compared with neighbouring areas.

Coral was absent, and species of algae that use calcium carbonate were displaced in favour of species that do not use it.

Snails were seen with their shells dissolving. There were no snails at all in zones with a pH of 7.4.

Meanwhile, seagrasses thrived, perhaps because they benefit from the extra carbon in the water.

These observations confirm that some of the processes seen in laboratory experiments and some of the predictions made by computer models of ocean ecosystems do also happen in the real world.

"I can't count the number of times that scientific talks end with 'responses have not yet been documented in the field'," said Elliott Norse, president of the Marine Conservation Biology Institute (MCBI).

"This paper puts that to rest for several ecologically important marine groups."

Point passed

The Intergovernmental Panel on Climate Change (IPCC) suggests that without measures to restrain carbon dioxide emissions, ocean pH is likely to fall to about 7.8 by 2100.

This suggests that some of the impacts seen around the Mediterranean vents might be widespread.

"I think we will see the same pattern in other parts of the world, because we're talking about keystone species such as mussels and limpets and barnacles being lost as pH drops," said Dr Hall-Spencer.

The IPCC suggests that some areas, notably the Southern Ocean, might feel the impacts at lower concentrations of CO2.

Last month, scientists reported that water with CO2 levels high enough to be "corrosive" to marine life was rising up off the western US coast.

Bottom water naturally contains more CO2 than at shallower depths. This scientific team argues that human emissions have pushed these levels even higher, contributing to pH values as low 7.5 in waters heavily used by US fishermen.

"If [pH 7.8] is a universal 'tipping point', then it indicates that sections of the western coast waters off North America may have passed this threshold during periods when this upwelling of waters high in CO2 occurs," commented Carol Turley from Plymouth Marine Laboratory (PML), who was not involved in the Mediterranean Sea study (PML is not affiliated with Plymouth University).

Emissions down

Organisms such as coral are also damaged by rising temperatures, and studies are ongoing into the combined effect of a warming and acidifying ocean.

There is much to learn. And during the coming week, scientists will announce the inauguration of the European Project on Ocean Acidification (Epoca), a four-year, 16m euro (£12.5m) initiative aiming to find some answers.

Studying the impacts may prove easier than doing anything about them.

"The reason that the oceans are becoming more acidic is because of the CO2 emissions that we are producing from burning fossil fuels," observed Dr Turley.

"Add CO2 to seawater and you get carbonic acid; it's simple chemistry, and therefore certain.

"This means that the only way of reducing the future impact of ocean acidification is the urgent, substantial reduction in CO2 emissions."