Intake of trace contaminants by corals in Abrolhos reef bank (western South Atlantic) during two decades of coastal impacts

Abstract

Abrolhos is the largest and most diverse coral reef system in the South Atlantic. It is home to several endemic coral species and a site of cetaceous reproduction. Like any other reef ecosystem worldwide, it experiences multiple disturbances associated with increasing sea surface temperatures, El Niño events, and, most recently, oil spill pollution. In addition to these global stressors, the Abrolhos region may have been impacted by coastal human interventions, a large-scale mining disaster, floods, and extra-tropical cyclones that affected the region during the last 20 years. Among these stressors, the Fundão dam collapse (the largest in the Southern Hemisphere) deserves special attention since it delivered significant amounts of iron tailings to the nearby coast. To investigate the region's recent history, we collected, dated, and performed detailed geochemical and isotopic analyses on two coral colonies (i.e., Siderastrea stellata and Mussismilia harttii), in order to determine if effects of recent human activity on reef systems (and most recent natural impacts) could be detected thorough bioaccumulation of metals in their skeletons. In this context, we detected an abrupt increase in Fe and Mn concentrations in the coral skeleton, which are among the main constituents of the Fundão dam tailings. We show that a concomitant increase in metal concentrations tracks contaminant dispersion of the Fundão dam tailings released to the western South Atlantic. Besides this event, our data also show that coastal dredging activities in the nearby coral reef site (i.e., at the Tomba channel) and two natural episodes (i.e., the flood of 2013 and the anomalous extra-tropical cyclonic activity in 2008) were also recorded in the coral skeleton based on changes in Rare Earth Elements distribution, Rb and U concentrations.