This paper reports the sequential voltammetric determination of Hg(II) and Cu(II) at the gold electrode (GE), and of Cu(II), Pb(II), Cd(II), Zn(II) at the hanging mercury drop electrode (HMDE) by differential pulse anodic stripping voltammetry (DPASV). Determination was performed in algae, potential environmental bio-monitor matrices, using 0.1 M HClO4 as supporting electrolyte. The sample digestion was also performed using a concentrated HCl-HNO3-H2SO4 acidic attack mixture. The analytical procedure was validated by the analysis of standard reference materials: Lagarosiphon Major (Aquatic Plant) BCR-CRM 060, Ulva Lactuca BCR-CRM 279 and Platihypnidium Riparioides BCR-CRM 061. For all elements in the certified matrices, in terms of repeatability, expressed as relative standard deviation (sr), precision was on order of 3-5%. In all cases, accuracy, expressed as relative error (e) was less than 6%, while the detection limits expressed in μg/g, dry weight, were in the 0.031-0.085 range. The analytical procedure was transferred and applied to algae, species Ulva Rigida and Gracilaria Rhodophita, sampled in two lagoon ecosystems connected to the Adriatic Sea (Italy): the Goro Bay, located at the mouth of the Po River, and the lagoon ecosystem located in proximity to Ravenna. To better validate the proposed method, a critical comparison with spectroscopic measurements is also discussed.