Performance of two Patagonian molluscs as trace metal biomonitors: The overlap bioaccumulation index (OBI) as an integrative tool for the management of marine ecosystems

In this study, we have investigated Cd, Cr, Cu, Ni, Pb and Zn in the biomonitors Mytilus chilensis and Nacella (P) magellanica sampled along seven selected sampling sites along 170 km of the coastal area of the Beagle Channel (Tierra del Fuego, Argentina) in four sampling campaigns: 2005, 2007, 2011 and 2012. The control charts were built by applying Johnson's probabilistic method for the first time in this marine area. We determined the metal concentration overlap ranges in the selected biomonitors (as well as medians and distribution), and the overlap bioaccumulation index (OBI) with respect to the lowest (OBI-L1) and the highest (OBI-L) extreme values of the overlap metal concentration ranges. The OBI can be used as an integrative tool in the management of prevailing unpolluted/ polluted marine coastal ecosystems. It consents to identify the most suitable organisms for managing several environmental conditions where an ecosystem quality control is needed. The OBI-L1 index can be employed as a preventive signal of alarm when the contamination process is in its early stages. For Cd, Ni, Cu and Cr, Nacella showed high OBI-L values that suggest its use as a biomonitor for mainly polluted marine ecosystems, in particular for Cd. Mytilus showed high Cd values for the OBI-L1 which means that this species is highly sensitive to a very low variation of the Cd levels in seawater. The OBI index enhances the observer's information variety about the performance of the molluscs as metal biomonitors in marine ecosystems. Eventually, here we propose to conceptualize the wide set of biomonitoring knowledge endowment as an open and evolutionary endowment of information variety supporting the environmental management.