Impact On Shellfish From Ocean Acidification
August 6, 2012

Impact On Shellfish From Ocean Acidification

redOrbit Staff & Wire Reports - Your Universe Online

In the journal Global Change Biology, a worldwide study is published to understand and forecast the likely impact of ocean acidification on shellfish and other marine life living in seas from the tropics to the north and south poles.

Ocean acidification is occurring because some of the increased carbon dioxide humans are adding to the atmosphere dissolves in the ocean and reacts with water to produce an acid.

According to the results, it is suggested that increased acidity is affecting the size and weight of shells and skeletons, and the trend across marine species is widespread. For marine predators such as tropical seabirds and seals, these animals are an important food source as well as being a valuable ingredient in human food production. These changes are likely to affect humans and the ocean's large animals the most.

The natural difference in shell thickness and skeletal size in four types of marine creatures living in 12 different environments from the tropics to the North and South Pole areas was investigated by UK Scientists from the British Antarctic Survey (BAS) and the National Oceanography Centre (NOC), together with colleagues from Australia's James Cook and Melbourne Universities and the National University of Singapore. Their plan was to get a clearer understanding of similarities and differences between species, and to make better predictions of how these animals might react to increasing acidity in the planet´s oceans.

Sea snails and other shellfish extract calcium carbonate from seawater to build their shells and skeletons. The effort required to do this varies from place to place in the world's oceans. The availability of calcium carbonate for species that produce carbonate skeletons is affected by a number of factors including temperature and pressure.

There is current evidence that ocean acidification is affecting the ability of some marine species to grow, especially during the early stages of life, and there is increasing concern about whether or not these species can develop or adapt to cope with higher levels in acidity in the coming years.

"Over evolutionary time, animals have adapted to living in environments where calcium carbonate is relatively difficult to obtain by forming lighter skeletons. Carbon dioxide from fossil fuel combustion is altering seawater chemistry in the same way, in a process called ocean acidification and this is making it harder for marine animals to make shells and skeletons," the study shows.

Clams, sea snails, lampshells and sea urchins were the four different types of marine animals examined. As the accessibility of calcium carbonate decreases, skeletons get lighter and account for a smaller part of the animal's weight, the scientists discovered. The fact that same effect occurs consistently in all four types suggests the effect is widespread across marine species, and that increasing ocean acidification will progressively reduce the availability of calcium carbonate.

"This effect is strongest at low temperatures and the results showed polar species to have the smallest and lightest skeleton, suggesting that they may be more at risk in the coming decades as the oceans change. Interestingly, where ecology requires animals to have strong skeletons - for instance to protect them from impacts from floating ice in Antarctica - skeletons are made thicker and stronger. However, they still form a smaller part of the animal's body mass, because the shape of the species changes to enclose much more body for a given amount of skeleton. Thus life finds a way, but still follows the overall trends of decreasing skeleton size in areas where the ocean chemistry makes it more difficult to obtain the necessary building blocks. If there is time for species to evolve in temperate and tropical regions it is one way they may be able to overcome some of the future effects of ocean acidification, according to Professor Lloyd Peck of British Antarctic Survey,

Furthermore, Dr. Sue-Ann Watson, formerly of the University of Southampton and British Antarctic Survey (now at James Cook University) said, "In areas of the world's oceans where it is hardest for marine creatures to make their limestone shell or skeleton, shellfish and other animals have adapted to natural environments where seawater chemistry makes shell-building materials difficult to obtain. Evolution has allowed shellfish to exist in these areas and, given enough time and a slow enough rate of change, evolution may again help these animals survive in our acidifying oceans."