# Biomonitoring of Heavy Metals: The Unexplored Role of Marine Sessile Taxa
## 2 Materials and Methods  
The present compilation is the result of an extensive bibliographic research on Elsevier's Scopus database (www.scopus.com), entering different keywords, \"heavy metal\" AND \"taxa\" and \"heavy metal\" AND \"common name of the organism\" (Figure 1), in the option \"Article title, Abstract, Keywords,\" in all years until the cut-off date of 20 June 2020. The literature considered in this work includes journal articles and grey literature, as congress proceedings. Systematic reviews are not included by choice. All documents found with the aforementioned queries have been screened by reading titles and abstracts, excluding those not matching our criteria (Figure 1), and only the ones eligible for this study have been considered for the analysis. Duplicates, e.g., same documents found using different keywords, were counted as one. Since the Mediterranean province showed the highest number of documents on the topic, we conducted an additional manual research on the references reported in the found articles, in order to include possible documents on the area that could have been missed with the online search (Figure 1). A flow chart of the searching strategy and the eligibility process is given as Figure 1.  
Studies from the web-based and manual researches have been analyzed based on the taxa considered (Porifera, Cnidaria, Bryozoa, Polychaeta, Cirrippedia, Tunicata), temporal distribution, marine realm of the sampling site(s), habitat (sea, estuarine), analyzed body part (cells and tissues, entire specimen, microbiome, skeleton), science field (biomonitoring, microbiology, physiology), HM(s), work setup (field, laboratory). Moreover, HMs considered in the documents have been divided in two categories, essential (Co, Cr, Cu, Fe, Mn,  
Figure 1: Flow chart illustrating the steps for obtaining documents about the study of heavy metals (HMs) on organisms from Scopus search engine and from the manual research. Mo, Ni, Se, V, and Zn) and nonessential (Ag, Al, As, Bi, Cd, Ce, Cs, Eu, Ga, Hf, Hg, La, Lu, Nb, Pb, Sb, Sc, Sn, Te, Th, Ti, U, Y, and Zr) elements following [26; 27; 28]. Documents related to the Mediterranean Sea province have been analyzed on the basis of the considered taxa (Porifera, Cnidaria, Polychaeta, Cirripedia, and Tunicata), temporal distribution, ecoregtion of the sampling site(s), sampling depth(s), HM(s), considered order(s) per taxa. In all the analyses, every document could be included in one or more categories. The analysis reported in Figure 2B was carried out following the bioregionalization of coastal and shelf areas proposed by [PERSON] et al. [29]. While, for the creation of the map of documents distribution in the Mediterranean Sea, geographic coordinates were used. In studies showing only a map of the sampling point(s), geographic coordinates were estimated from it. In the absence of a map, coordinates of the sampling point(s) were estimated using the information across the text, if available. When the given coordinates ended up in land, they were adjusted to the nearest coastal points. Figure 2: Map showing the number of documents per: (**A**) first authors’ affiliation country and (**B**) marine realm. A list of works divided per taxa with all document's details (publication year, authors, title, DOI/Reference, source, first author affiliation country, realm of the sampling site, habitat, basic physicochemical parameters of water, taxa, application field, analyzed body part, data validation, HM(s), and work setup) is reported in the Supplementary Material as Table S1. The Supplementary Material also included a detailed list of documents (taxa, authors, publication year, marine ecoregion of the sampling site(s), latitude, longitude, depth, application field, order of the analyzed species, analyzed species, HM(s), concentration, and unit) on the Mediterranean Sea province as Table S2. In the case of HMs, concentrations were not reported along the text, they were estimated from graphs.