Impact of high pCO2 and warmer temperatures on the process of silica biomineralization in the sponge Mycale grandis

Siliceous sponges have survived pre-historical mass extinction events caused by ocean acidification and recent studies suggest that siliceous sponges will continue to resist predicted increases in ocean acidity. In this study, we monitored silica biomineralization in the Hawaiian sponge Mycale grandis under predicted pCO(2) and sea surface temperature scenarios for 2100. Our goal was to determine if spicule biomineralization was enhanced or repressed by ocean acidification and thermal stress by monitoring silica uptake rates during short-term (48 h) experiments and comparing biomineralized tissue ratios before and after a long-term (26 d) experiment. In the short-term experiment, we found that silica uptake rates were not impacted by high pCO(2) (1050 mu atm), warmer temperatures (27 degrees C), or combined high pCO(2) with warmer temperature (1119 mu atm; 27 degrees C) treatments. The long-term exposure experiments revealed no effect on survival or growth rates of M. grandis to high pCO(2) (1198 mu atm), warmer temperatures (25.6 degrees C), or combined high pCO(2) with warmer temperature (1225 mu atm, 25.7 degrees C) treatments, indicating that M. grandis will continue to prosper under predicted increases in pCO(2) and sea surface temperature. However, ash-free dry weight to dry weight ratios, subtylostyle lengths, and silicified weight to dry weight ratios decreased under conditions of high pCO(2) and combined pCO(2) warmer temperature treatments. Our results show that rising ocean acidity and temperature have marginal negative effects on spicule biomineralization and will not affect sponge survival rates of M. grandis.