Polycarpa aurata as biomonitor to assess potential toxic elements across the Coral Triangle

Coral reefs are increasingly threatened by multiple stressors, including pollution from potentially toxic trace elements (PTEs) released in the environment by many human activities, like widespread industrial and artisanal/small-scale gold mines (ASGMs), especially in the Coral Triangle. In the present study, concentration of 12 PTEs (Al, As, Ba, Cr, Cu, Hg, Fe, Mn, Mo, Sb, V, and Zn) in suspended particulate matter and their bioaccumulation in tissues (tunic and body without tunic) of the ascidian Polycarpa aurata were investigated by inductively coupled plasma mass spectrometry at four putative impact sites, downstream of four mining areas with different industrial and ASGM activities, and at four control sites in the North Sulawesi, Indonesia. Compared to control sites, P. aurata significantly accumulates Hg, Cu, and V in the tunic and, with higher values, Hg, Cu, Mo, and Cr (respectively, up to 3.35 ± 0.71, 12.63 ± 1.52, 9.58 ± 1.48, and 1.60 ± 0.47 μg g−1) in the rest of the body, especially in the presence of less regulated mining activities (i.e., ASGMs). Mercury showed a bioaccumulation factor for suspended particulate matter greater than 1 at all sites. As a combination of easy-to-recognize and sample, widespread, and very abundant throughout the Coral Triangle, an efficient filter feeder resistant to pollution, very effective in accumulating potentially toxic trace elements, especially mercury, copper, and chromium, P. aurata may be considered as an ideal biomonitor organism. To measure PTEs contamination, this species should be included in monitoring programs throughout the Coral Triangle by developing a proper standard protocol.