Scientists were puzzled by the higher-than-expected amounts of carbonate in the top levels of the water. Until now, scientists have believed that the oceans' calcium carbonate came from the external 'skeletons' of microscopic marine plankton.
A recent study estimates that three to 15 per cent of marine calcium carbonate is in fact produced by fish in their intestines and then excreted. This is a conservative estimate and the team believes it has the potential to be three times higher.
The team estimated the total mass of bony fish in the ocean at between 812 million tons and 2,050 million tons, which they said could produce around 110 million tons of calcium carbonate per year.
The carbonate produced by fish is soluble and dissolves in the upper sea water, while that from the plankton sinks to the bottom, the team noted.
The researchers predict that future increases in sea temperature and rising CO2 will cause fish to produce even more calcium carbonate.
Fish Guts Explain Marine Carbon Cycle Mystery
ScienceDaily 15 Jan 09;
New research reveals the major influence of fish on maintaining the delicate pH balance of our oceans, vital for the health of coral reefs and other marine life.
The discovery, made by a team of scientists from the UK, US and Canada, could help solve a mystery that has puzzled marine chemists for decades. Published 16 January 2009 in Science, the study provides new insights into the marine carbon cycle, which is undergoing rapid change as a result of global CO2 emissions.
Until now, scientists have believed that the oceans' calcium carbonate, which dissolves to make seawater alkaline, came from the external 'skeletons' of microscopic marine plankton. This study estimates that three to 15 per cent of marine calcium carbonate is in fact produced by fish in their intestines and then excreted. This is a conservative estimate and the team believes it has the potential to be three times higher.
Fish are therefore responsible for contributing a major but previously unrecognised portion of the inorganic carbon that maintains the ocean's acidity balance. The researchers predict that future increases in sea temperature and rising CO2 will cause fish to produce even more calcium carbonate.
To reach these results, the team created two independent computer models which for the first time estimated the total mass of fish in the ocean. They found there are between 812 and 2050 million tonnes (between 812 billion and 2050 billion kilos) of bony fish in the ocean. They then used lab research to establish that these fish produce around 110 million tonnes (110 billion kilos) of calcium carbonate per year.
Calcium carbonate is a white, chalky material that helps control the delicate acidity balance, or pH, of sea water. pH balance is vital for the health of marine ecosystems, including coral reefs, and important in controlling how easily the ocean will absorb and buffer future increases in atmospheric CO2.
This calcium carbonate is being produced by bony fish, a group that includes 90% of marine fish species but not sharks or rays. These fish continuously drink seawater to avoid dehydration. This exposes them to an excess of ingested calcium, which they precipitate into calcium carbonate crystals in the gut. The fish then simply excrete these unwanted chalky solids, sometimes called 'gut rocks', in a process that is separate from digestion and production of faeces.
The study reveals that carbonates excreted by fish are chemically quite different from those produced by plankton. This helps explain a phenomenon that has perplexed oceanographers: the sea becomes more alkaline at much shallower depths than expected. The carbonates produced by microscopic plankton should not be responsible for this alkalinity change, because they sink to much deeper depths intact, often becoming locked up in sediments and rocks for millions of years. In contrast, fish excrete more soluble forms of calcium carbonate that are likely to completely dissolve at much shallower depths (e.g. 500 to 1,000 metres).
Lead author Dr Rod Wilson of the University of Exeter (UK) said: "Our most conservative estimates suggest three to 15 per cent of the oceans' carbonates come from fish, but this range could be up to three times higher. We also know that fish carbonates differ considerably from those produced by plankton. Together, these findings may help answer a long-standing puzzle facing marine chemists, but they also reveal limitations to our current understanding of the marine carbon cycle."
And what about the future? The researchers predict that the combination of increases in sea temperature and rising CO2 expected over this century will cause fish to produce even more calcium carbonate. This is for two reasons. Firstly, higher temperatures stimulate overall metabolism in fish, which drives all their biological processes to run faster. Secondly, increasing CO2 in their blood directly stimulates carbonate production by the gut specifically.
Dr Rod Wilson continues: "We have really only just scratched the surface of knowing the chemistry and fate of fish carbonates. Given current concerns about the acidification of our seas through global CO2 emissions, it is more important than ever that we understand how the pH balance of the sea is normally maintained. Because of the impact of global climate change, fish are likely to have an even bigger influence on the chemistry of our oceans in future. So, it is vitally important that we build on this research to help fully understand these processes and how this will affect some of our most precious marine ecosystems."
This study was carried out by the University of Exeter (UK), University of Miami (USA), University of Ottawa (Canada), University of British Columbia (Canada), Centre for Environment, Fisheries and Aquaculture Science (UK) and University of East Anglia (UK).
Dr Rod Wilson's research was supported by the Biotechnology and Biological Sciences Research Council (BBSRC).
Fish poop helps balance ocean's acid levels
Yahoo News 15 Jan 09;
WASHINGTON – The ocean's delicate acid balance may be getting help from an unexpected source, fish poop. The increase in carbon dioxide in the atmosphere not only drives global warming, but also raises the amount of CO2 dissolved in ocean water, tending to make it more acid, potentially a threat to sea life.
Alkaline chemicals like calcium carbonate can help balance this acid. Scientists had thought the main source for this balancing chemical was the shells of marine plankton, but they were puzzled by the higher-than-expected amounts of carbonate in the top levels of the water.
Now researchers led by Rod W. Wilson of the University of Exeter in England report in the journal Science that marine fish contribute between 3 percent and 15 percent of total carbonate.
And the contribution may be even higher than that, say the researchers from the U.S., Canada and England.
They report that bony fish, a group that includes 90 percent of marine species, produce carbonate to dispose of the excess calcium they ingest in seawater. This forms into calcium carbonate crystals in the gut and the fish then simply excrete these "gut rocks."
The process is separate from digestion and production of feces, according to the researchers.
The team estimated the total mass of bony fish in the ocean at between 812 million tons and 2,050 million tons, which they said could produce around 110 million tons of calcium carbonate per year.
The carbonate produced by fish is soluble and dissolves in the upper sea water, while that from the plankton sinks to the bottom, the team noted.
The research was funded by the U.K. Biotechnology and Biological Sciences Research Council, The Royal Society, the U.S. National Science Foundation, the Natural Sciences and Engineering Research Council of Canada, United Nations Environmental Program, the Pew Charitable Trust and the U.K. Department of Environment, Food and Rural Affairs.
Fish Digestions Help Keep The Oceans Healthy
Michael Kahn, PlanetArk 16 Jan 09;
LONDON - The digestive systems of fish play a vital role in maintaining the health of the oceans and moderating climate change, researchers said on Thursday.
Computer models showed how bony fish produced a large portion of the inorganic carbon that helps maintain the oceans' acidity balance and was vital for marine life, they said.
The world's bony fish population, estimated at between 812 million and 2 billion tons, helped to limit the consequences of climate change through its effect on the carbon cycle, University of British Columbia researchers reported in the journal Science.
"This study is really the first glimpse of the huge impact fish have on our carbon cycle -- and why we need them in the ocean," researcher Villy Christensen and colleagues wrote.
Calcium carbonate is a white, chalky material that helps control the acidity balance of sea water and is essential to the health of marine ecosystems and coral reefs.
It helps regulate how much carbon dioxide oceans would be able to absorb from the atmosphere in the future, the researchers said.
Until now, scientists believed calcium carbonate came from microscopic marine plankton. The new findings suggested between 3 percent and 15 percent of the material comes from bony fish, said Rod Wilson of the University of Exeter in Britain, who worked on the study.
Bony fish, which include about 90 percent of marine species but not sharks or rays, produce calcium carbonate that forms crystals in the gut and is then excreted in chalky solids.
"Because of the impact of global climate change, fish are likely to have an even bigger influence on the chemistry of our oceans in the future," Wilson said in a statement.
(Editing by Nick Vinocur)
