Investigating temperature influences on shell growth and microstructural variations in bay scallops: insights from multiscale microscopy

Scallops (order Pectinida) are well-known for their robust and beautiful calcitic shells that protect them from external impacts and predators. Scallops respond to environmental conditions, including water temperature, salinity, and food supply, which are reflected in the shell growth rates and patterning. The bay scallop (Argopecten irradians) is a species of high ecological and aquacultural value in North America, and its habitat may expand towards higher latitudes with inevitable global warming. To investigate the effect of water temperature on the accretion rate and the polycrystalline microstructure of the Bay scallop shell, we conducted a controlled growth experiment on juveniles, 4 weeks following their larval metamorphosis. Approximately 400 individuals, collected from a hatchery 4 weeks after metamorphosis, were then reared in reconstituted seawater for 9 weeks at 23 °C and 26 °C. At 7-, 9-, 11-, and 13-weeks post-metamorphosis, calcein was added to the water for 7 hours for fluorescent staining, and then equal batches of scallops were collected and fixed. Morphologic characterization of bay scallop shells included micro-computed X-ray tomography for 3D measurements to measure shell thickness, and fluorescence light microscopy for accretion rate assessment. We used mechanical testing of complete shells in compression to assess their stiffness, strength and toughness. Microstructural analysis of the shells included scanning electron microscopy and crystallographic analysis by electron backscattered diffraction. The scallops reared in warmer water exhibited a faster growth rate with shells showing higher calcite grain misorientation, no difference in relative shell thickness, and inconclusive difference in the shell mechanical properties. This study may help us to understand the multifarious implications of climate change.