Effects of anthropogenic seawater acidification on acid–base balance in the sea urchin Psammechinus miliaris

The purple-tipped sea urchin, Psammechinus miliaris, was exposed to artificially acidified seawater treatments (pH w 6.16, 6.63 or 7.44) over a period of 8 days. Urchin mortality of 100% was observed at pH w 6.16 after 7 days and coincided with a pronounced hypercapnia in the coelomic fluid producin...

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Bibliographic Details
Published in:	Marine pollution bulletin 2007, Vol.54 (1), p.89-96
Main Authors:	Miles, Hayley, Widdicombe, Stephen, Spicer, John I., Hall-Spencer, Jason
Format:	Article
Language:	eng
Subjects:	Acid-Base Equilibrium - physiology Acid–base balance Animal, plant and microbial ecology Animals Applied ecology Bicarbonates - analysis Biological and medical sciences Carbon dioxide Carbon Dioxide - analysis Carbon Dioxide - physiology Carbon sequestration Echinodermata Echinoida Echinoidea Ecotoxicology, biological effects of pollution Fundamental and applied biological sciences. Psychology Hydrogen-Ion Concentration Hypercapnia Invertebrates Magnesium - analysis Marine Marine and brackish environment Ocean acidification Psammechinus miliaris Sea Urchins - metabolism Seawater - chemistry
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Summary:	The purple-tipped sea urchin, Psammechinus miliaris, was exposed to artificially acidified seawater treatments (pH w 6.16, 6.63 or 7.44) over a period of 8 days. Urchin mortality of 100% was observed at pH w 6.16 after 7 days and coincided with a pronounced hypercapnia in the coelomic fluid producing an irrecoverable acidosis. Coelomic fluid acid–base measures showed that an accumulation of CO 2 and a significant reduction in pH occurred in all treatments compared with controls. Bicarbonate buffering was employed in each case, reducing the resultant acidosis, but compensation was incomplete even under moderate environmental hypercapnia. Significant test dissolution was inferred from observable increases in the Mg 2+ concentration of the coelomic fluid under all pH treatments. We show that a chronic reduction of surface water pH to below 7.5 would be severely detrimental to the acid–base balance of this predominantly intertidal species; despite its ability to tolerate fluctuations in pCO 2 and pH in the rock pool environment. The absence of respiratory pigment (or any substantial protein in the coelomic fluid), a poor capacity for ionic regulation and dependency on a magnesium calcite test, make echinoids particularly vulnerable to anthropogenic acidification. Geological sequestration leaks may result in dramatic localised pH reductions, e.g. pH 5.8. P. miliaris is intolerant of pH 6.16 seawater and significant mortality is seen at pH 6.63.
ISSN:	0025-326X 1879-3363