ECHINOMETRA VIRIDIS EXHIBITS SEASONAL RESPONSE IN CALCIFICATION RATES TO PREDICTED END OF 21ST CENTURY CO2-INDUCED OCEAN ACIDIFICATION

Atmospheric carbon dioxide (pCO­₂) has increased from ca. 280 to 400 ppm since the onset of the Industrial Revolution, with current models predicting levels as high as 900 ppm by the end of this century. This increase in atmospheric pCO₂ will lower oceanic pH, thereby affecting the ability of calcifying marine organisms to build their shells and skeletons. To test the effects of predicted end-of-century ocean acidification on the tropical urchin Echinometra viridis, specimens were reared under current and predicted end-of-century atmospheric pCO₂ at the urchin’s summer and winter temperatures with three-way replication. The actual pCO₂ and temperature values for the four treatments (± standard error) were: (1) 20.3±0.1 °C and 524±33 ppm; (2) 20.6±0.1 °C and 827±32 ppm; (3) 30.0±0.1 °C and 448±27 ppm; and (4) 29.9±0.1 °C and 783±45 ppm. Calcification rates over the 60-day experimental period, estimated as %-change in buoyant weight, were (1) 1.3 ± 3.9, (2) -14.6 ± 7.5, (3) 15.9 ± 4.1, and (4) 3.9 ± 4.7%, respectively. Analysis of variance (ANOVA) of the results revealed that calcification rates increased with increasing temperatures (p = 0.01085) and decreased with increasing pCO₂ (p = 0.01043). These results suggest that the tropical urchin E. viridis will be negatively impacted by CO₂-induced ocean acidification that is predicted to occur by the end of this century, and that these impacts will be more severe in the winter and in cooler, higher latitude waters.