The first global analysis of carbon stored in seagrass meadows in the world’s oceans shows they can hold as much carbon as Earth’s temperate and tropical forests.
Researchers also estimate that although seagrass meadows occupy less than 0.2% of the world’s oceans, they are responsible for more than 10% of all ‘blue carbon’ stores buried annually in the ocean and rival carbon stores in the extensive peat deposits of mangroves.
Results gathered from 3,640 observations of 946 distinct seagrass meadows across the globe found that coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometre, mostly in the soils below them. In comparison, a typical land forest stores around 30,000 metric tons per square kilometre.
The study, "Seagrass Ecosystems as a Globally Significant Carbon Stock", was published in the journal Nature Geoscience and provides further evidence of the important role the world’s declining seagrass meadows play in mitigating climate change.
Data sets as deep as one metre were concentrated in Florida Bay in the US, along the Spanish coast of the Western Mediterranean and in Shark Bay in Western Australia. The greatest concentration of carbon found was in the Mediterranean, where seagrass meadows stored carbon many metres deep.
According to the findings, seagrass meadows store 90% of their carbon in the soil and continue to build on this indefinitely, with some seagrass clones reported to be older than 100,000 years.
But a second group of researchers has estimated that warming of the Mediterranean this century, under a moderately optimistic scenario of greenhouse gas emissions, is likely to cause the extinction of seagrass meadows.
The first study was led by Dr James Fourqurean, a professor of biology at Florida International University. He said the results showed that seagrass meadows were key sites for carbon storage and were probably far more important as carbon dioxide sinks than had been realised.
Seagrass meadows are among the world’s most threatened ecosystems and some 29% of all historic meadows have been destroyed, mainly because of dredging and degradation of water quality, while a further 1.5% of the meadows are lost each year.
The researchers estimate that destruction of the meadows could potentially emit up to 25% as much carbon as deforestation on land.
But if the meadows were restored, they could effectively and rapidly re-establish lost carbon sinks and stores as well as providing a range of other valuable ecosystem benefits. These include improvements in water quality and as an important biodiversity habitat.
The second study of the Mediterranean seagrass meadows involved researchers at the University of Western Australia and the Spanish National Research Council.
The international team examined the trajectory of the density of western Mediterranean meadows during the 21st century under estimated warming based on 10 global climate models and two regional models.
Researchers used the relationships between the annual mortality rate of seagrass and the maximum annual temperature to predict annual mortality rates in future. The result was a 90% decrease in shoot density by 2050, with all models predicting a rapid warming of surface seawater, leading to an increase in the frequency and intensity of heatwaves.
The models predict the average surface temperature of seawater during the summer would be 3.4°C warmer by the end of this century compared with today. They also forecast that from 2050 on, seawater temperature will exceed 28°C, the threshold temperature triggering mortality of seagrass every summer.
An article on Mediterranean seagrass vulnerable to regional climate warming was published online in the journal Nature Climate Change. It warns that actions to mitigate local impacts, although beneficial, are not enough to increase seagrass resistance to warming.
The swiftest action, mitigation of local disturbances by 2010, would delay the functional extinction of the meadow by a decade, but only by two years if mitigation of local stresses were achieved by 2030.
The researchers concluded that rapid international action to reduce emissions of greenhouse gases, at levels well below those considered in the study, was the only solution capable of ensuring the ancient ecosystem persisted throughout the 21st century.
Researchers also estimate that although seagrass meadows occupy less than 0.2% of the world’s oceans, they are responsible for more than 10% of all ‘blue carbon’ stores buried annually in the ocean and rival carbon stores in the extensive peat deposits of mangroves.
Results gathered from 3,640 observations of 946 distinct seagrass meadows across the globe found that coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometre, mostly in the soils below them. In comparison, a typical land forest stores around 30,000 metric tons per square kilometre.
The study, "Seagrass Ecosystems as a Globally Significant Carbon Stock", was published in the journal Nature Geoscience and provides further evidence of the important role the world’s declining seagrass meadows play in mitigating climate change.
Data sets as deep as one metre were concentrated in Florida Bay in the US, along the Spanish coast of the Western Mediterranean and in Shark Bay in Western Australia. The greatest concentration of carbon found was in the Mediterranean, where seagrass meadows stored carbon many metres deep.
According to the findings, seagrass meadows store 90% of their carbon in the soil and continue to build on this indefinitely, with some seagrass clones reported to be older than 100,000 years.
But a second group of researchers has estimated that warming of the Mediterranean this century, under a moderately optimistic scenario of greenhouse gas emissions, is likely to cause the extinction of seagrass meadows.
The first study was led by Dr James Fourqurean, a professor of biology at Florida International University. He said the results showed that seagrass meadows were key sites for carbon storage and were probably far more important as carbon dioxide sinks than had been realised.
Seagrass meadows are among the world’s most threatened ecosystems and some 29% of all historic meadows have been destroyed, mainly because of dredging and degradation of water quality, while a further 1.5% of the meadows are lost each year.
The researchers estimate that destruction of the meadows could potentially emit up to 25% as much carbon as deforestation on land.
But if the meadows were restored, they could effectively and rapidly re-establish lost carbon sinks and stores as well as providing a range of other valuable ecosystem benefits. These include improvements in water quality and as an important biodiversity habitat.
The second study of the Mediterranean seagrass meadows involved researchers at the University of Western Australia and the Spanish National Research Council.
The international team examined the trajectory of the density of western Mediterranean meadows during the 21st century under estimated warming based on 10 global climate models and two regional models.
Researchers used the relationships between the annual mortality rate of seagrass and the maximum annual temperature to predict annual mortality rates in future. The result was a 90% decrease in shoot density by 2050, with all models predicting a rapid warming of surface seawater, leading to an increase in the frequency and intensity of heatwaves.
The models predict the average surface temperature of seawater during the summer would be 3.4°C warmer by the end of this century compared with today. They also forecast that from 2050 on, seawater temperature will exceed 28°C, the threshold temperature triggering mortality of seagrass every summer.
An article on Mediterranean seagrass vulnerable to regional climate warming was published online in the journal Nature Climate Change. It warns that actions to mitigate local impacts, although beneficial, are not enough to increase seagrass resistance to warming.
The swiftest action, mitigation of local disturbances by 2010, would delay the functional extinction of the meadow by a decade, but only by two years if mitigation of local stresses were achieved by 2030.
The researchers concluded that rapid international action to reduce emissions of greenhouse gases, at levels well below those considered in the study, was the only solution capable of ensuring the ancient ecosystem persisted throughout the 21st century.
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