Abstract
Recent studies have documented variation in skeletal structure and carbonate mineralogy across a broad range of marine invertebrate taxa. Intraspecific changes in growth, morphology, and carbonate composition may occur in response to local and global changes in temperature, carbonate saturation state, and nutrient availability. Recurring upwelling along the west coast of the United States creates an alongshore mosaic of Ocean Acidification (OA), which may induce plastic responses and/or select for adaptive skeletal construction that can withstand pCO2 and temperature changes. Calcifying bryozoans provide a unique study system for investigating carbonate precipitation under variable conditions. Using a newly constructed flow-through CO2 control apparatus, we tested whether three laboratory-reared populations of the bryozoans Membranipora serrilamella, M. tuberculata and Celleporella cornuta showed differences in growth, calcification, and skeletal composition in response to simulated future OA conditions. Under elevated pCO2 (1200 mu atm), bryozoans showed no significant differences in growth rate (new zooids added) compared to clones reared under current atmospheric values. However, C. cornuta colonies raised under high CO2 were significantly lighter, with less carbonate per zooid compared to colonies grown in present-day conditions (400 mu atm). Scanning electron microscopy revealed that elevated pCO2 led to dissolution of bryozoan skeletons, which did not occur at 400 mu atm. Structural changes in M. tuberculata and C. cornuta colonies may be related to the dissolution of high magnesium calcite skeletal components. Analyses of bryozoan morphological responses along with environmental proxies (delta 13C, delta 18O, and Mg/Ca ratios) could yield high resolution records of temperature and pH, which could be used to help reconstruct environmental variation along the California coast.