Abstract
Oysters and other bivalve shellfish assimilate elements from the environment into their shell and soft tissues, making them potentially useful bioindicators of pollution to local waters. Unlike soft tissues, shell material is not readily metabolized and may provide a temporally explicit record of past pollution exposure. To determine if shell can be used as a bioindicator of pollution similarly to soft tissues (as a proxy for tissues) and how relationships between shell and tissue might vary with pollution sources or environmental conditions, we used solution-based Inductively Coupled Plasma Mass Spectrometry to measure trace metal concentrations in shell and soft tissues of native and lab-reared oysters. Native oysters were obtained from restored reef sites in LA, MS, and AL, with different expected pollution from nearby anthropogenic sources, and Lab-reared oysters were exposed to different types of contaminated water at two salinities (25, 14) to test a common local environmental variable. Overall, trace metal concentrations in shell increased with concentrations in tissue, with the values in tissue explaining 50% (native), 43% (lab-25), and 33% (lab-14) of variation in shell values. Mg and V were conserved (assimilated near 1:1) between shell and tissues in all treatments. Variation between shell and tissue was higher at lower salinity. These data indicate that shell can be a direct proxy for tissue for some elements and at least predictive for others but may be affected by environmental conditions such as salinity. Salinity may be particularly important to interpreting bioindicator data because it affects both oyster physiology and bioavailability of trace metals in the environment. This method, therefore, has high potential for use to reconstruct historical pollution events, such as the Deepwater oil spill, and may be most informative when other conditions that affect oyster physiology and trace metal bioavailability are also considered.
