TEMPERATURE-DEPENDENT VARIATION IN BIOMINERALIZATION IN MARINE BIVALVE MOLLUSKS (NUCULIDAE)

Changing ocean conditions impact marine organisms by altering their ability to perform essential life functions. Understanding how different ocean conditions, in particular temperature, impact processes of biomineralization is critical for anticipating the impacts of ongoing climate change on marine life. For this study we investigated how biomineralization in the calcifying bivalve mollusk family Nuculidae varies geographically with environmental conditions in order to provide insight into how these organisms may respond to current and future warming. Previous work suggests that calcifying marine organisms will tend to grow larger crystals in warmer ocean water, and that these crystals will exhibit greater heterogeneity in their orientations. We are testing these hypotheses as part of an ongoing study involving the analysis of live-collected and historical Nuculidae specimens from locations around the globe. The microstructure of Nuculidae is composed of prismatic and nacre crystal layers. Nacre is a structure composed of calcium carbonate crystalline tablets separated by an organic matrix in a layout comparable to brick and mortar. Using a scanning electron microscope, we gathered data on the thickness of calcium carbonate tablets in the nacre layer of individual bivalve shells; our current dataset consists of 14,750 tablets and 70 individual specimens. Using x-ray photoemission electron microscopy imaging, ongoing work is also focused on measured heterogeneity in crystal orientations. These two biomineralization measures were then compared to sea surface temperatures at collection sites to look for temperature-related trends in biomineralization. Our initial analyses document a statistically significant positive relationship between nacre tablet thickness (TT) and sea surface temperature (SST) (p < 0.001). This suggests that TT may increase in the future as climate change progresses, which may have implications for the resilience of particular shellfish to shell dissolution and degradation in a more acidic ocean. In the future we intend to analyze our x-ray photoemission electron microscopy data for live-dead shifts in crystal orientation and size in the Gulf of Mexico and determine if the relationship between TT and SST is observed within individual genera.