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Marine ecosystem under threat

DELWYN DICKEY
Last updated 07:45 21/02/2013
Mussels

EXPANSION: A report by the NIWA is soon to be released and includes research on the effects of a more acidic and warmer ocean on young shellfish.

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As aquaculture looks set to expand in this northern area the industry is facing a new challenge - dealing with the impacts on shellfish production from rising ocean acidification due to climate change.

A report by the National Institute of Water and Atmosphere - NIWA - for the Ministry of Primary Industries is soon to be released and includes research on the ne effects of a more acidic and warmer ocean on young shellfish with implications for the aquaculture industry.

It has been known for some years that increasing levels of carbon dioxide (CO2) in the atmosphere is seeing more CO2 being absorbed into the oceans, making sea water more acidic.

This is just starting to affect the early and most vulnerable stages of shellfish development, along with shell plankton - pteropods, and could have serious consequences for marine ecosystems in the future.

Carbonate found in sea water is used by young shellfish to make their first shell in their first few days of life.

As sea water becomes more acidic it reduces the levels of carnonate in the water to a level where larvae struggle to make their shells. This affects their growth and their weakened shells leave them vulnerable to predators. Still higher acidity levels will see shells already formed start to dissolve.

The same pH scale as used with sea water as on land for soil. The alkaline end of the scale is 14, the acidic end is 0 with 7 being considered neutral.

Sea water is actually in the alkaline end of the scale.

Since pre industrial times the oceans pH has dropped from 8.2 to 8.1. As the pH is heading toward the acidic end of the scale the water is considered to becoming more acidic.

While 0.1 of a unit might not seem a lot the pH scale works like the Richter scale for earthquakes, and this equates to a 30 percent rise in acidity, over the last 250 years.

But with scientists now expecting pH to drop to about 7.8 by 2100 this equates to a further increase in acidity of 150 percent in just 90 years.

"What we're seeing here is really sudden changes to the levels of pH. In the past we've had these changes over millions of years where as here it is tens of years," says Associate Professor Mary Sewell at the University of Auckland's School of Biological Sciences working in the field of ocean acidification and evolutionary biology.
"The question is can they [shellfish]adapt - we don't really know."

The impacts could be devastating on marine ecosystems, she says.

"In some parts of the world - particularly parts of Asia, a good portion of their food comes from the ocean. Oysters are a big portion of the food that people eat - where they get their protein from. This has major implications, she says.

"Not just as shellfish may get very expensive to buy as they will be harder to grow, but also in terms of food security," she says.

While commercial shellfish production will also be affected as much of the youngstock - spat - comes from wild stock there are some options currently being researched which are likely to stave off serious impacts on the aquaculture industry in the short to medium term at least.

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Auckland and Northland already account for almost all of the country's pacific oyster production, and a quarter of Greenshell mussels, with plans by Northland Aquaculture Development to raise their output worth $1million to $20m in coming years.

There are also plans for a northland oyster and paua hatchery and mussel spat research.

Last week independent freshwater, coastal marine and environmental research specialists the Cawthron Institute announced they had signed a $26 million, seven year contract with MPI and SPATZnz to selectively breed mussel spat.

Already the countries only commercial supplier of Pacific oyster spat, the first significant quantities of commercial mussel spat bred in a closed loop rather than from wild stock are expected by 2015.

Cawthron's senior scientist head of the cultured shellfish programme, Nick King says he too has concerns for marine ecosystems in the future and says it's good that acidification is being talked about.

"Evolution may not be able to keep up. It's important to demonstrate the potential effects if things go as bad as they could."

Commercial production of spat will give some protection to the likes of paua, mussel and oyster, he says.

"The first stage of commercially dealing with acidification will be to modify the sea water used in spat production - take the water chemistry back to what it was in pre industrial times. They're researching this in the US and it's not as easy as it sounds," he says.

Keeping the spat for a little longer so its shell is thicker and can withstand the slightly more corrosive natural seawater is also on the cards.

"The second stage is breeding shellfish that can handle those conditions but this may not be needed for 50 years as adult shellfish can hold out for some time - this is affecting the really delicate life stage for now.

Research is under way in commercial shellfish hatcheries on the west coast of Oregon and Washington State.

Spikes in sea water CO2 levels used in oyster production caused by periodic "upwelling" of CO2 rich water from the ocean floor killed nearly all the farms spat for two years running back in 2007/8 with problems continuing. Modelling suggests this upwelling combined with increased CO2 levels from the atmosphere could have a profound impact on the United States west coasts marine ecosystems in just forty years, a report in Science magazine says.

 "We don't have that kind of upwelling system in New Zealand but we do we have a different problem," Professor Sewell says.

"A lot of our aquaculture areas are in protected estuaries and bays, especially the oyster and mussel industry - the Bay of Islands, in the Firth of Thames and the Marlborough Sounds - where they really want to expand production.

"They are subjected to a lot of land run off. So you can get a lot of algae blooms in the system from lots of nutrients coming in from runoff from farms or industrial sources. As these die off and are broken down CO2 is also released. So CO2 comes in from the atmosphere but also from farm and urban runoff," she says.

"The situation in New Zealand is slightly different to the US but it could give us a big wake up call for what could happen in the future."

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