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Fish on acid lose fear of predators

April 15, 2014 in Adaptation, Carbon Dioxide, Marine ecology, Ocean acidification

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Reef species like this clown fish are at higher risk of succumbing to predators in more acid seas Image: Ritiks via Wikimedia Commons

Reef species like this clown fish are at higher risk of succumbing to predators in more acid seas
Image: Ritiks via Wikimedia Commons

By Tim Radford

As carbon dioxide makes the seas more acidic and poses physical problems for some species of fish, it can also rob them of their inhibitions, which helps their predators.

LONDON, 15 April – Coral reef fishes exposed to acid oceans lose their sense of smell – and their sense of caution – and are more likely to fall prey to natural enemies, according to new research in Nature Climate Change.

The finding is based on observations of the behaviour of four species at a reef off the coasts of Papua New Guinea where natural carbon dioxide seeps out of the rock, and confirms a series of other such studies in the last year.

A cool volcanic discharge in the reef has served as a natural laboratory for years: water in the region reaches an average pH of 7.8. This standard measure of acidity is co-incidentally the level predicted for all the world’s oceans by 2100, as atmospheric carbon dioxide levels continue to rise, according to the Intergovernmental Panel on Climate Change. www.ipcc.ch/

Australian and US scientists observed the fishy behaviour from a boat moored above the reef, and also tested the fish on board the vessel. What they observed was that, away from the volcanic bubbles of carbon dioxide, in conditions of more normal ocean chemistry, damsel fish and cardinal fish seemed able to smell predators and stayed in sheltered places in the reef to avoid becoming prey.

Fish from the waters richer in carbonic acid seemed not to sense the presence of predators, and were more likely to venture into dangerous waters.

Survival threat

After a sudden scare that sent all the fish racing for cover, the fish from the bubble reef ventured forth much sooner. In normal circumstances, such fish spend 80% of their time under cover.

The bubble reef fish spent at most only 12% of their time in hiding. Mortality accordingly was five times higher.
“Their sense of smell was acutely affected in CO2-rich waters in ways that gravely threaten their survival,” said Alistair Cheal of the Australian Institute of Marine Science.

“We were able to test long-term realistic effects in this environment,” said another author, Danielle Dixson of the Georgia Institute of Technology in the US. “One problem with ocean acidification research is that it’s all laboratory-based, or you’re testing something that’s going to happen in 100 years’ time with fish that are from the present day, which is not actually accurate.”

The reasoning is that the change in pH levels disrupts a neuroreceptor in the fishes’ brains and affects faculties or alters behaviour. Similar experiments with Californian rockfish have demonstrated much the same effect.

Acid spreading

But increased acidification of the oceans is also likely to affect shellfish and corals in other ways, and research in the Great Barrier Reef region of Australia has documented a dramatic behaviour change in a jumping snail that suggested impaired decision-making capability as pH levels alter.

Sea water is already 30% more acidic that it was at the start of the Industrial Revolution 200 years ago. The rate of change is at least 100 times faster than at any time in the last 650,000 years.

The bubbling waters of the reef under test are not unique – such localized carbonic acid seeps occur in many places all over the world – and the fact that predators might find easy pickings in such places makes no real difference to population levels in the vastness of the rest of the ocean. But such experiments raise the question: can ecosystems adapt to changing water chemistry?

“Continuous exposure does not reduce the effect of high CO2 on behaviour in natural reef habitat and this could be a serious problem for fish communities in the future when ocean acidification becomes widespread as a result of continued uptake of anthropogenic CO2 emissions,” the authors conclude. - Climate News Network

Shellfish feel impact of more acid seas

January 22, 2014 in Adaptation, Algae, Carbon Dioxide, Fish, Greenhouse Gases, Marine ecology, Ocean acidification, Predation, USA

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Low oxygen and rising acidity in the oceans spell trouble for some species of scallop Image: By Jeremy Keith from Brighton & Hove, UK

Low oxygen and rising acidity in the oceans spell trouble for some species of scallop
Image: By Jeremy Keith from Brighton & Hove, UK, via Wikimedia Commons

By Tim Radford

Researchers in the US have discovered that several more marine species are being damaged by the effects of the increasing acidity of the oceans, a direct consequence of greenhouse gas emissions.

LONDON, 22 January – Ocean acidification brings fresh problems for Californian native oysters. Like some creature from a horror movie, a driller killer threatens Ostrea lurida, the Olympia oyster that dwells in the estuaries of western North America.

Many species are likely to face problems as pH levels (which measure how acid a liquid is) change and ocean chemistry begins to alter as the world warms and ever more dissolved carbon dioxide flows into the sea and adds to its acidity.

Researchers have observed that coral skeletons are affected and larval oysters find it more difficult to build their first shell structures. The change towards greater acidity seems to trigger learning difficulties in juvenile rockfish  and make it harder for the conch snail to leap out of the way of a predator’s poisoned dart. And three separate research papers bring yet more bad news for yet more sea creatures.

Eric Sanford and colleagues at the University of California, Davis, report in the Proceedings of the Royal Society B that under more acid water conditions, the Olympia oyster experiences a 20% increase in drilling predation.

Researchers conducted a direct experiment involving oysters reared in normal conditions, oysters reared in water high in dissolved carbon dioxide, and an invasive predator from a distant ocean called Urosalpinx cinerea, the Atlantic oyster drill. Their assumption was that bivalves (creatures with a hinged shell) in more acid water would grow thinner shells, and that drilling predators would selectively choose the victims that would be easiest to drill into.

Problems multiply

It didn’t work quite like that – the experimental oysters did not have thinner shells. But these oysters were victims all the same. They were 30% to 40% smaller than the control group of oysters in the other tank “and these smaller individuals were consumed at disproportionately greater rates”, the authors say. The invasive snails, on the other hand, were not bothered by the change in water pH.

The results indicate, say the researchers, that ocean acidification “can negatively affect the early life stages of Olympia oysters.” They have been subjected already to overfishing, disease, habitat loss, pollution and hypoxia, when water is so rich in nutrients that it becomes starved of oxygen and turns into a dead zone where nothing much can survive for long. Extra vulnerability to an invasive driller killer is, the scientists carefully say in non-emotive language, “a relatively novel stressor for this species.”

Hypoxia, too, turns out to be a problem made worse by carbon dioxide. Low oxygen waters are already acidified waters, say Christopher Gobler of Stony Brook University in the US and colleagues in the Public Library of Science journal PLOS One.

They report that a combination of low oxygen and low pH led to higher rates of death and slower growth for young bay scallops and hard clams than expected from either individual factor. “Low oxygen zones in coastal and open ocean ecosystems have expanded in recent decades, a trend that will accelerate with climatic warming”, says Gobler.

Threat to algae

“There is a growing recognition that low oxygen regions of the ocean are also acidified, a condition that will intensify with rising levels of atmospheric CO2 due to the burning of fossil fuels causing ocean acidification. Hence the low oxygen, low pH conditions used in this study will be increasingly common in the world’s oceans in the future.”

And ocean acidification is not just making life good for predators and bad for the prey, it could be threatening to alter the basic biodiversity of the sea. Sophie McCoy of the University of Chicago reports in Ecology Letters that she and Cathy Pfister looked at the dynamics of coralline algae that live around Tatoosh Island, Washington, on the Pacific coast of the US.

These little creatures, like oysters, grow calcium carbonate skeletons. In previous observations in which four species were transplanted to these waters, one species called Pseudolithophyllum muricatum emerged as the undisputed winner. In the 1980s, its skeleton grew twice as thick as its competitors’.

In the latest round of tests, there was no clear winner: no species was dominant, and P. muricatum won less than 25% of the time – a response, the authors think, to changes in the pH of the sea water just in the last 12 years.

The total energy available to the organisms was the same, but their responses were different: those that needed to make more calcium carbonate tissue were under more stress than those that did not.

This experiment was a “real world” test rather than a laboratory experiment. “Field sites like Tatoosh are unique because we have a lot of historical ecological data going back decades,” said McCoy. “I think it is really important to use that in nature to understand what is going on.” – Climate News Network

Researchers study shellfish success

December 24, 2013 in Adaptation, Antarctic, Europe, Fish, Marine ecology, Ocean acidification

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Scottish musel beds: The European research will be globally relevant Image: Copyright and courtesy of SAMS

Scottish mussel beds: The European research will be globally relevant
Image: Copyright and courtesy of SAMS

By Alex Kirby

The British Antarctic Survey is leading a research programme aimed at helping the European fishing industry and monitoring the effects of climate change on several shellfish species.

LONDON, 24 December – If you like the occasional plate of grilled scallops or fancy an oyster now and then, read on and ponder. The health of several species of European shellfish is under threat.

The bad news is that the shellfish face an uncertain future as the oceans become warmer and more acidic because of the changing climate. But there is some better news too: the European Union is funding an international research team to work out how these changes will affect several species vital to the European fishing economy and to marine biodiversity.

Scientists do not fully understand how shellfish like oysters, mussels, scallops and clams produce their shells, or how a change in environment will affect their populations. To address this the EU is funding a €3.6 million (£3 m) programme called CACHE (Calcium in a Changing Environment). Shellfish are an important part of the European marine economy which provides an estimated 5.4 million jobs.

Coordinated from the British Antarctic Survey (BAS) in Cambridge, UK, the programme will research how the animals produce their shells. The scientists will also try to identify populations which are resilient to climate change.

These relatively small animals are important as part of the wider pattern of marine biodiversity. And, as they make their shells from calcium carbonate, they also help to absorb the greenhouse gas CO2 from seawater.

Biotech applications

The risk to them comes from their dependence on calcium carbonate – a substance which dissolves under acidic conditions.  As the oceans become warmer and more acidic their shells will either thin, or the animals will have to expend more energy on producing thicker shells.  This will affect their population sizes and the quality of their flesh, directly affecting fisheries and consumers.

How shellfish produce their shells also matters to the biotech industry, which is interested in imitating (in a process known as bio-mimicry) the way in which shellfish take a soluble compound like calcium to make solid, robust structures.

A better understanding of this could reduce the carbon footprint of producing construction materials and create the potential for “fixing” CO2 into the building process.

The species the research team is looking at are the king scallop, the Pacific oyster, the blue mussel and the soft shell clam. It will also study the native oyster to help conservation plans, as it is listed as a priority species in the UK.

Iceberg protection

Dr Melody Clark of BAS, the programme coordinator, told the Climate News Network: “The programme is driven by the science. We really don’t know the fundamentals of how shellfish respond to changing environments.

“We do know that, in response to environmental conditions, they can change how much shell they produce, for example growing thicker shells in response to predators. In the Antarctic, inter-tidal limpets grow much thicker shells than sub-tidal ones, because they are bashed by icebergs.

“And we don’t know just how they make their shells, whether with calcium from their food, or from the seawater.

“On bio-mimicry, this research may let us start to develop ways of producing more robust structures without carbon, and with little energy.

“We’re researching shellfish in European waters, but we’re recruiting the researchers worldwide, and the results will be relevant beyond Europe.” – Climate News Network