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

Abstract

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 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 (Biometrika 36: 149-175, 1949) 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, Cr, Cu, and Ni, 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. Good OBI-L1 values were instead obtained for Mytilus for Cr and Cu, showing the good aptitude of these organisms to detect minimum variations of trace metals concentrations in seawater. The OBI index and its related guidelines have both theoretical and practical implications in environmental management. They can be used, for instance, in environmental prevention from events such as oil spills or other marine disasters. Marine ecosystems are complex systems. According to the Ashby's Law (1957, 1958), the understanding of a complex system (requisite variety) depends on the information variety owned by the observer. 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.

Managing complexity of marine ecosystems: From the monitoring breakdown structure (MBS) to the baseline assessment. Trace metal concentrations in biomonitors of the Beagle Channel, Patagonia (2005–2012)

“…The overall median is 3.71 µg/g while the confidence interval is in the range 0.98-9.96 µg/g. This is also consistent with the overlap bioaccumulation indexes (OBI) previously obtained for these biomonitors (Conti et al, 2019). Mytilus resulted highly sensitive to low seawater Cd concentrations (OBI-L1 = 5.16), which means it detects fivefold lower Cd levels in seawater with respect to the minimum overlap range according to Johnson's method.…”

“…The application of the normalization procedure has been carried out through the use of the SuppDists package of R (Wheeler 2013). In our previous study (Conti et al, 2019) we used the control charts to build the overlap bioaccumulation index (OBI). In this study, the control charts for the selected biomonitors were built for the first time to determine differences among sites, i.e.…”

“…Table 1 Metal concentrations in the selected biomonitors for the 2011-2012 sampling campaigns in the Beagle Channel (mean ± SD, µg/g dry weight) a (Conti et al, 2019); metal concentrations in coastal seawater samples, (ng/L) (mean ± SD) (n = 7 stations) and CFs b × 10 3 . a Data for N. magellanica in muscle and viscera were standardized by using the method reported in Conti et al (2012b).…”

“…Conversely, Nacella showed higher bioaccumulation Cd surplus, e.g. OBI-L = 4.98 which means it detects about five times higher Cd levels with respect to the upper extreme overlap range (see for details Conti et al, 2019).…”

“…The selection of biomonitors depends on their proved ability in metal assumption and to detect even minimal differences in the marine ecosystem accurately. This is strongly related with environmental management which needs reliable information consistent with the complexity of the marine ecosystems (requisite variety) (Ashby, 1957(Ashby, , 1958Conti et al, 2019) in order to take decisions at the early stage of the contamination processes (i.e. prevention programs).…”