Long-term exposure to elevated pCO2 more than warming modifies early-life shell growth in a temperate gastropod

Co-occurring global change drivers, such as ocean warming and acidification, can have large impacts on the behaviour, physiology, and health of marine organisms. However, whilst early-life stages are thought to be most sensitive to these impacts, little is known about the individual level processes by which such impacts take place. Here, using mesocosm experiments simulating ocean warming (OW) and ocean acidification (OA) conditions expected for the NE Atlantic region by 2100 using a variety of treatments of elevated pCO(2) and temperature. We investigated their impacts on bio-mineralization, microstructure, and ontogeny of Nucella lapillus (L.) juveniles, a common gastropod predator that exerts important top-down controls on biodiversity patterns in temperate rocky shores. The shell of juveniles hatched in mesocosms during a 14 month long experiment were analysed using micro-CT scanning, 3D geometric morphometrics, and scanning-electron microscopy. Elevated temperature and age determined shell density, length, width, thickness, elemental chemistry, shape, and shell surface damages. However, co-occurring elevated pCO(2) modified the impacts of elevated temperature, in line with expected changes in carbonate chemistry driven by temperature. Young N. lapillus from acidified treatments had weaker shells and were therefore expected to be more vulnerable to predation and environmental pressures such as wave action. However, in some instances, the effects of both higher CO2 content and elevated temperature appeared to have reversed as the individuals aged. This study suggests that compensatory development may therefore occur, and that expected increases in juvenile mortality under OA and OW may be counteracted, to some degree, by high plasticity in shell formation in this species. This feature may prove advantageous for N. lapillus community dynamics in near-future conditions.