Effects of the 1982-1983 El Niño mega event on bivalve mollusk biomineralization
Marine bivalve mollusks are valued as climate change recorders due to predictable growth rates and the recording of the ambient seawater environment into their shells (e.g., temperature, dissolved inorganic carbon (DIC)). Bivalves that endure extreme environmental perturbations also exhibit alteration of the shell microstructure in response to the stress. Numerous studies demonstrate correlations between shell isotopic values and environmental parameters, such as δ^18O and temperature, but the possibility of confounding isotopic signatures between shell layers and microstructures in a single organism, induced by environmental stress factors, has not been sufficiently studied. Two bivalve species (Trachycardium procerum and Chione subrugosa), collected from the Peruvian coast after the 1982-1983 El Niño, exhibit microstructural alterations in the shell in correlation with the sea surface temperature (SST) anomaly during the event. Common biomineral alterations include changes in the relative thickness of certain microstructural types and the loss of intercrystalline organic matrix components. δ^18O_shell and δ^13C_shell data show no significant changes in correlation with the El Niño growth scar in any shell layers of T. procerum. C. subrugosa, an intertidal species, shows δ^13C_shell and δ^18O_shell depletion in the affected area. These data indicate that biomineralization changes are not synchronized with isotopic signatures. Furthermore, bivalve biogeochemical proxies may not be sufficiently sensitive to detect rapid fluctuations in SST, but potentially useful in detecting other localized El Niño associated events, such as an increase in rainfall.