How rising carbon dioxide levels can dissolve the shells of sea creatures.
By now we’re familiar with apocalyptic visions of a scorched and flooded world ravished by global warming. But this gloomy prognosis is now set to take a nosedive beneath the ocean waves.
A European study has produced hard evidence that our profligate production of the greenhouse gas CO2 (carbon dioxide) is likely to have far reaching consequences for life offshore. Its findings could spell disaster for the edible mussel and the pacific oyster, two species that play an essential role in the marine food chains and support a $10.5 billion global industry.
Researchers at several European universities examined how the mussels and oysters were able to produce the calcium carbonate they needed to make their shells as they increased the CO2 in the atmosphere. They were particularly interested in how their development was affected by acidification, the process by which water becomes more acidic as it absorbs CO2.
Every day over 25 million tons of CO2 is soaked up by seawater, gradually making it more acidic. Marine pH levels are now dropping at a rate at least 100 times greater than any point during the last 600,000 years. The results of the study were stark: at levels of atmospheric CO2 expected by the year 2100 – 740 parts per million – the speed at which shells were produced fell by 25pc in mussels and 10pc in oysters. Significantly they also found that mussel shells would dissolve when CO2 in the atmosphere reaches 1800 ppm.
The results have prompted fears of irreversible damage to coastal ecosystems and the communities that have depended on them for centuries. The burgeoning worldwide shellfish market has grown by 8pc a year for the last 30 years. Production levels reached 12 million tons a year in 2002, 10.8pc of which were pacific oysters and 3.6pc of which were mussels. Beyond this, mussels and oysters also help to create habitats for other species, by controlling the flow of oceanic material and are the stable diet of several varieties of marine bird.
The study was carried out by Frédéric Gazeau, a scientist at the Netherlands Institute of Ecology, and his colleagues, including Jean-Pierre Gattuso, director of research at the Oceanographic laboratory at Villefranche-sur-Mer (CNRS/Université Pierre et Marie Curie). Mr Gattuso said that further studies were needed as a matter of urgency. “The impact on molluscs’ fishing and culture is difficult to assess because our publication is the first one on this topic and is lab-based,” he said. “Potential consequences, such as a longer time to reach commercial size, increased susceptibility to predators and increased mortality of early life stages, now need to be fully investigated.”
The researchers will now assess the long-term impact of the phenomenon by examining how easily mussels and oysters can genetically adapt to produce their shells in a more acidic environment. But real world evidence is less gloomy than this study suggests. Anecdotal accounts from UK shell fishermen, especially those on the Yorkshire Coast where the richest grounds are to be found, say that crab, lobster and mussel stocks are at their best for years.
How does acidification threaten shellfish?
What is the wider threat?
“The negative impact of ocean acidification on calcification of marine organisms has now been demonstrated in a large number of groups such as corals, macroalgae, phytoplankton, molluscs and echinoderms. The gravest consequences seem to be for coral reefs, the very existence of which entirely relies on calcification.”
The heat is on.
The world’s seas currently take up one tonne of this carbon dioxide for each person on the planet every year. But the ocean’s effectiveness as a carbon sink will decrease as acidification takes place and it is also thought that rising ocean temperatures would further reduce its ability to soak up CO2. Mr Gattuso said there needed to be more studies into the effect on the ocean’s ability to absorb CO2.
What can we do?