HEAVY METAL FORAMS: LIVING WITH TRACE METALS IN TEXAS COASTAL BAYS

As in many estuaries, living foraminifera along the Texas Gulf Coast are subject to various natural and anthropogenic perturbations. In Nueces, Copano, Mission, and Mesquite Bays, stressors include extremes in temperature, salinity, and dissolved oxygen. Elevated levels of trace metals may also be a concern. Dissolved Pb and Cu, as well as Zn in sediments, have exceeded Texas Commission on Environmental Quality (TCEQ) criteria in Nueces Bay. Though they do not exceed TCEQ criteria, elevated levels of heavy metals, including Ba, are also found in the sediments of Nueces, Copano, and Mission Bays. Mesquite Bay, in comparison, is considered a pristine standard. While population numbers of foraminifera are generally healthy, evidence of stress in the bays is shown from test dissolution and the formation of framboidal pyrite. Test dissolution occurs in living individuals, mostly Ammonia parkinsoniana, and involves the loss of many chambers or entire outer whorls. Framboidal pyrite fills chambers of various species, is found disseminated in sediment, and is sometimes observed in living specimens. Previous papers have proposed that presence of heavy metals may stress foraminifera, causing bacterial attack and setting up a microenvironment conducive to pyritization and dissolution. More test dissolution and pyrite production seem to occur in bays with higher levels of trace metals. In an effort to better understand the variables that may act to cause dissolution and pyritization, major and minor elements, including Fe, Ba, Pb, and Zn, in living A. parkinsoniana tests are being analyzed with ICP-MS. Past research involving response of foraminifera to trace metals in sediments has mainly focused on shell deformation and population dynamics. The few papers looking at incorporation of heavy metals into tests do show that foraminifera pick up trace metals in highly polluted environments. It is expected that living foraminiferal tests from Nueces Bay will show heavy metal enrichment, and it will be interesting to see whether or not lesser amounts of heavy metals from the other bays will also be incorporated into shells.