Comparative bioactivity analysis of hard corals: antioxidant and antimicrobial responses three years after the MV Wakashio oil spill in Mauritius

In 2020, the MV Wakashio spilled 1000 tons of low-sulphur fuel oil along the south-east coast of Mauritius. This study aimed to compare the bioactivity of healthy hard corals with those affected by the oil spill, three years after the incident. Acropora selago, Pocillopora damicornis, Millepora alcicornis, and Porites rus were collected from affected and unaffected regions. Extracts were prepared through solvent extraction and fractioning with ethyl acetate and hexane, followed by antioxidant activity analysis using the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay and antimicrobial testing via disc diffusion. All species exhibited significant antioxidant activity (p < 0.05), with P. rus showing the highest radical scavenging activity (RSA), 9.04 % and crude extracts demonstrating the strongest overall bioactivity. Bacillus subtilis, Staphylococcus aureus and Escherichia coli were resistant to all extracts. Only crude extracts of A. selago, M. alcicornis, and P. rus (among other fractions) could inhibit Pseudomonas aeruginosa, with A. selago exhibiting the largest inhibition zone (10.56 mm). No significant bioactivity differences were found between corals of oil-affected and unaffected regions, possibly due to the floating and rapid dispersion of low-sulphur fuel on the water surface. These findings highlight the pharmaceutical potential of hard corals and suggest further research on species-specific and environmental factors.