Starfish and sea urchins counteract our carbon emissions

Out of the estimated 5.5 gigatonnes of carbon emitted each year by human activities, about 1.8 percent are removed from the air and stored by echinoderms such as starfish, sea urchins, brittle stars and sea lilies. This makes them less important “carbon sinkers” than plankton, but the finding is still significant since no one expected them to catch such a large chunk of our wayward carbon.

The new discovery is the result of a study* led by Mario Lebrato**, PhD student at the Leibniz Institute of Marine Science. The work was done when he was at the National Oceanography Centre, Southampton (NOCS) and affiliated with the University of Southampton’s School of Ocean and Earth Science (SOES).

“I was definitely surprised by the magnitude of the values reported in this study, but [the study’s] approach seems sound, so the reported numbers are probably fairly accurate,” says palaeoceanographer Justin Ries of the University of North Carolina at Chapel Hill.

Ries also points out that these important creatures might be affected by ocean acidification.

“If the echinoderms end up being disproportionately susceptible to ocean acidification then it’s conceivable that the dissolving of echinoderm-derived sediments will be one of the earliest effects of ocean acidification on the global carbon cycle,” he explains. “In fact, maybe it already is.”
The body of an echinoderm consists of up to 80% calcium carbonate and according to the Lebrato study these hard-shelled animals collectively capture 100 billion tons of carbon each year.

“The realisation that these creatures represent such a significant part of the ocean carbon sink needs to be taken into account in computer models of the biological pump and its effect on global climate“, says Lebrato. “Our research highlights the poor understanding of large-scale carbon processes associated with calcifying animals such as echinoderms and tackles some of the uncertainties in the oceanic calcium carbonate budget. The scientific community needs to reconsider the role of benthic processes in the marine calcium carbonate cycle. This is a crucial but understudied compartment of the global marine carbon cycle, which has been of key importance throughout Earth history and it is still at present.”

The study has been published in the journal ESA Ecological Monographs.

* Mario Lebrato, Debora Iglesias-Rodriguez, Richard Feely, Dana Greeley, Daniel Jones, Nadia Suarez-Bosche, Richard Lampitt, Joan Cartes, Darryl Green, Belinda Alker (2009) Global contribution of echinoderms to the marine carbon cycle: a re-assessment of the oceanic CaCO3 budget and the benthic compartments. Ecological Monographs. doi: 10.1890/09-0553.

** mlebrato13 [at]googlemail.com