Elevated pCO2 Reduces Calcification Rates and Alters Skeletal Microstructure in Three Calcifying Marine Invertebrate Species

This study investigates ocean acidification effects on calcification rates and skeletal microstructure in marine calcifying invertebrates within the context of marine ecology and ocean acidification biology, an area of growing scientific importance given its implications for coastal shellfish aquaculture management, marine protected area design, and ocean acidification policy. Using controlled mesocosm incubations at four pCO2 levels with alkalinity anomaly calcification measurement and SEM skeletal microstructural imaging, we examine aragonite and calcite saturation state decline under elevated pCO2 reducing net calcification and increasing skeletal dissolution rates in 36 mesocosm tanks (9 per species per pCO2 treatment) incubated for 56 days drawn from flow-through seawater mesocosm facility at Bodega Bay Marine Laboratory. Results indicate that calcification rates decline significantly at pCO2 > 600 ppm in all three species, with net calcification becoming negative (net dissolution) in coralline alga at 1100 ppm, and SEM imaging revealing progressive dissolution microstructure at the species-specific dissolution threshold (p < 0.001), with 58.4% calcification reduction in oysters at 1100 ppm versus 400 ppm as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to marine ecology and ocean acidification biology and carry actionable implications for the design of programs and policies targeting coastal shellfish aquaculture management, marine protected area design, and ocean acidification policy.