An international study, coordinated by IRD and Paleosofia APEMA (Italy), shows that the reduction in size observed in certain marine organisms during mass extinctions in the past could be the result of ocean acidification. The smaller size would have helped the species to survive in higher concentrations of CO2, a phenomenon which may reoccur in the future with global warming. These results were published in the journal Nature Climate Change on 20 April 2015.
An international team of marine biologists and palaeontologists studied how marine gastropods (sea snails) withstand acidification in the oceans. To do so, they used natural CO2 sources, e.g. sites of volcanic gas emission in Sicily, as test sites to simulate the modification of seawater chemistry produced in past eras and likely to reoccur in the future.
The results of their study were published in journal Nature Climate Change on 20 April 2015 and explain why marine species that survived previous mass extinctions linked to ocean acidification were greatly reduced in size, a phenomenon known as the ‘Lilliput effect’. They provide compelling evidence on the impact that ocean acidification could have on marine ecosystems unless the quantities of carbon dioxide discharged into the atmosphere are slashed.
According to Vittorio Garilli (Paleosofia‐APEMA, Italy), co-director of the study, ‘two snail species living near CO2 sources in shallow water were almost one third smaller than those gathered in normal pH conditions. They have adapted their metabolic rates to cope with the acidified seawater. These physiological changes allowed the animals to maintain calcification and to partially repair shell dissolution.’
Some snails were studied at the IAEI laboratory of environmental studies in Monaco, where their calcification rates were measured in aquariums. Riccardo Rodolfo‐Metalpa (IRD, New Caledonia), the study’s other director, explains: ‘these organisms have developed an astonishing capacity for calcification and resistance to shell dissolution, in pH conditions that were considered too low for calcification at all. The organisms, which are exposed to high levels of CO2 over multiple generations, provide clues to the changes we can expect in marine ecosystems as CO2 emissions continue to rise uncontrollably and also explain previous mass extinctions.’
Jason Hall Spencer (Plymouth University, UK) and Marco Milazzo (Palermo University) add: ‘these snails show similar variations in size as those observed in fossil organisms. What is more, the results highlight the physiological benefits of dwarfism.’
Richard Twitchett, (Natural History Museum, London) continues: “fossil archives show that mass extinctions and the emergence of dwarfism in certain marine shellfish have been repeatedly linked to previous episodes of global warming. Similar changes will probably affect an increasing number of marine ecosystems, especially given the speed at when ocean acidification and warming are occurring.’
Jason Hall Spencer concludes: “it is vital that we develop understanding of the mechanisms that help certain species survive when exposed to very high levels of CO2, because gas emissions are already having negative effects on marine trophic networks and threatening food security.’