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Sargassum duplicatum and Padina tetrastromatica seaweed species collected from oil and a non-oil extraction site at Madura Island were investigated in this study for selected bioactivities, heavy metals and toxicity effects. The collected seaweeds were evaluated for their phytochemical constituents, total phenolic contents (TPC), antioxidant activities, antidiabetic activities, anticancer activities, toxicities and heavy metals using Folin-Ciocalteus method, the 2,2-diphernyl-1 picrylhydrazyl (DPPH), α-glucosidase enzyme, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Brine Shrimp Lethality Test (BSLT) and atomic absorption spectrophotometer, respectively. The crude extracts (C), normal hexane (N), ethyl acetate (E), and methanol residue fractions (M) were studied. The highest TPC (589.79 ± 7.14 mg GAE/g) was observed in ethyl acetate fraction of P. tetrastromatica from the non-oil extraction site. Meanwhile, the crude extracts and all fractions showed potent antioxidant, antidiabetic, and cytotoxic activities with ethyl acetate fraction of P. tetrastromatica from non-oil extraction site displaying the highest effects (IC50 25.25 ± 5.15, 249.12 ± 1.77 and 70.56 ± 2.56 µg/mL: antioxidant, antidiabetic, cytotoxic activities respectively). In the brine shrimp assay, the crude extracts and all fractions of both species from the two sites were non-toxic with exception of the hexane fraction of P. tetrastromatica from oil site which was very toxic after 24 h incubation. However, the crude extract of S. duplicatum and ethyl acetate fraction of P. tetrastromatica from oil extraction site were mildly toxic except the hexane fraction of P. tetrastromatica from oil site which was very toxic after 48 h incubation while samples of both species from the non-oil site were nontoxic. In each species, the concentration of Cd from the oil extraction site was higher than those of the non-oil site with the values of P. tetrastromatica leading and a similar observation occurred Cu in P. tetrastromatica but the same Cu was negligible in S. duplicatum as Pb was negligible in both species. According to the findings of this current study, it is safe to conclude that both S. duplicatum and P. tetrastromatica from Madura Island have antioxidant, antidiabetic and cytotoxic activity, we therefore recommend these species from the non-oil extraction site for drug candidates against the various health abnormally they seem to inhibit.

Caulerpa is one of the seaweed that grows naturally in Indonesian waters such as those in Mandangin Island. This study aimed to identify Caulerpa sp. based on molecular analysis using certain genetic markers. This research is expected to provide information on the identification of macroalgae from Indonesia waters, especially Mandangin Island, Madura with the use of molecular analysis based on 18SrRNA primers. The two green seaweed samples from the Caulerpa genus in this study were successfully analyzed using 18SrRNA primers. The BLAST results of samples 1and 2 are related to Caulerpa taxifolia 18SrRNA, but in the phylogenetic tree result, Sample 1 was more closely related to Caulerpa sertularioides f. longipes. 18SrRNA primers have been used for molecular identification of green seaweed from Mandangin for the first time and this shows that barcode markers can be used for molecular identification of seaweed, specifically Caulerpa in the waters of Mandangin Island, Indonesia.