Sea stars bury much more carbon than anticipated

January 8th, 2010 - 5:58 pm ICT by ANI  

London, January 8 (ANI): A new study has determined that animals such as sea stars, sea urchins and sea lilies bury much more carbon than anticipated.

Studies of biological carbon in the oceans tend to focus on organisms that drift through the shallows, such as plankton, because they are known to store carbon in the form of calcium carbonate, which they transport to the sea floor when they die.

According to a report in Nature News, Mario Lebrato, a PhD student at the Leibniz Institute of Marine Science in Germany, suspected that bottom-dwelling animals such as echinoderms also store large amounts of calcium carbonate, and wondered how large a role they might have in the global carbon cycle.

While still an undergraduate at the University of Southampton, UK, Lebrato set out to study the rates at which echinoderms absorb calcium carbonate and what happens to the carbon when they die.

Lebrato and his colleagues collected echinoderm samples from both deep sea and shallower waters at multiple latitudes in the Atlantic Ocean.

At every stop, they tried to collect a few echinoderms from each of the phylum’s five main classes: sea stars (Asteroidea), sea urchins (Echinoidea), brittle starts (Ophiuroidea), sea cucumbers (Holothuroidea) and sea lilies (Crinoidea).

Only fully-grown adult animals were collected, and all were cleaned thoroughly before being freeze dried and disintegrated into powder for carbon analysis.

The team calculated carbon measurements for the classes that they collected at all sample sites.

They then used these data to inform estimates of carbon content for echinoderms collected at various latitudes from other oceans around the world.

The researchers later paired their carbon estimates with population density and mortality data for the different echinoderm classes worldwide to determine how much calcium carbonate full-sized animals store in their bodies and how quickly that carbon was buried by sediment after the animals die.

Lebrato and his colleagues report that worldwide, echinoderms capture around 0.1 gigatonnes of carbon per year.

This is less than the global capture resulting from pelagic organisms - a figure that ranges from 0.4 to 1.8 gigatonnes depending on the sources considered - but still represents a sizeable carbon pump.

By comparison, human activities lead to around 5.5 gigatonnes of carbon being pumped into the air every year.

According to Craig Smith, a biological oceanographer at the University of Hawaii at Manoa, the numbers that this study reveals are probably an underestimate because vast regions of the Equatorial Pacific have high echinoderm biomass but are not well studied. (ANI)

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