Marine ecosystems harbor a remarkable chemical diversity that remains largely unexplored, with marine invertebrates standing out as prolific producers of bioactive secondary metabolites. Viral diseases continue to pose major challenges, both for aquaculture—where outbreaks compromise productivity and sustainability—and for human health, where effective treatments are still lacking against many pathogens.

In this context, the present study investigated the antiviral activity of crude extracts obtained from two nudibranchs (NA and NB), one holothurian (PS), and one soft coral (CR). Extracts were tested against a panel of eight viruses, including human respiratory viruses (HCoV-229E, hMPV, RSV, IAV) and fish viruses (VHSV, CyHV-3, TiLV, CCPV), using complementary in vitro assays that evaluated direct virucidal effects, pre-treatment of host cells, and continuous exposure during infection.

The nudibranch extracts exhibited the strongest and most consistent antiviral effects, significantly reducing infection across both human and fish viruses. In contrast, the holothurian extract showed selective antiviral activity but was limited by cytotoxicity at certain concentrations. The results suggest that nudibranchs contain metabolites with broad-spectrum antiviral potential, acting through mechanisms that may involve both viral inactivation and cellular protection.

These findings are highly relevant for the development of innovative strategies in aquaculture, where sustainable viral control remains a critical bottleneck, and they also highlight promising prospects for human therapeutics. By demonstrating the value of marine biodiversity as a reservoir of novel antiviral agents, this work underscores the importance of sustainable marine bioprospecting as part of the Blue Economy, advancing marine biotechnology toward solutions with cross-sectoral impact.