Seventeen out of forty thousand. The ratio looks poor and is not. Medicinal chemistry has far lower success rates starting from molecules designed on paper, and the seventeen are not just any drugs: cytarabine for leukaemia and vidarabine against herpes, both born of a Caribbean sponge in the 1950s, the cone snail’s painkiller, the anticancer agents we will cover in the coming pieces. But the number that matters most is another. None of these molecules was invented. They were read. An organism had written them over millions of years, to defend itself, to hunt, to avoid being eaten while standing still, and a chemist copied them.
There is a paradox inside this story, and the series will return to it often. The organism that is collected is often not the one that makes the molecule. Carroll and colleagues counted the classes of compounds isolated from marine invertebrates and attributed with certainty to symbiotic bacteria: forty-six. The average time between finding the molecule in the animal and finding the bacterium that makes it is more than fifteen years. And in most cases that bacterium cannot be cultured: it lives only inside its host. Whoever wants the molecule must have the animal, or synthesise it from scratch after seeing it.

And here the objection comes, and it is a fair one. Once the molecule is found, the animal is no longer needed: it is synthesised. True, and the sea hare we will cover tomorrow proves it. But synthesis comes afterwards. First you need the organism, whole, alive, with its symbionts inside. Nobody has ever designed a conotoxin or a dolastatin on paper: they read them in an animal. Driving a species extinct does not burn a factory. It burns a book nobody has opened yet.
The books are burning at a rate that can be measured. The IUCN Red List, updated on 9 July 2026, counts 175,909 species assessed and 49,505 threatened with extinction. The latest update brought in the molluscs of deep-sea hydrothermal vents: more than half of those that depend on the vents are threatened by seabed mining, which has not yet begun on an industrial scale. Coral reefs, the main reservoir of marine chemistry, are worse off. In November 2024 the IUCN reassessed 892 species of warm-water reef-building corals: 44 per cent are threatened, against a third in 2008. Counting the data-deficient species, the range runs from 38 to 51 per cent. Between January 2023 and March 2025 bleaching-level heat stress hit 84 per cent of the world’s reefs, in 82 countries. In the first global event, in 1998, it was 21 per cent.

The cone snail that gave us ziconotide lives on those reefs. The sponges, the tunicates, the sea hares, the bryozoans: almost everything this series will describe lives on those reefs or on the seabeds that people want to mine. No adjectives are needed. Whoever destroys a marine species impoverishes the planet twice: once now, in the ecosystem, and once later, in the medicine that species could have given to someone not yet born.
This series will tell one molecule at a time: where it came from, who found it, what it did in the clinic, what it did not do. With real numbers and primary sources, not press releases. In 1983 this writer opened a column with the same title, «Marine Pharmacology & Toxicology», in La Conchiglia and The Shell, with Berardino Porfirio. The first article was called «Prospects» and said that the sea covers more than 70 per cent of the globe, that 160,000 species live in it, and that only a few hundred of them had been studied from a pharmacological point of view. A year later, in the second part of an article on antineoplastic substances from the sea, we wrote that the only anticancer drug of marine origin in clinical use was cytarabine. Forty-three years later, some of those prospects have become drugs, some have failed, some are still waiting. The series picks up from there. Tomorrow, the first story: a sea hare from the Indian Ocean, 1,600 kilograms of animals, a few milligrams of poison, and eight drugs.

Percentage of the world’s coral reefs hit by bleaching-level heat stress in the four global events recorded: 1998, 2010, 2014–2017 and 2023–2025 (data to 30 March 2025). Chart produced by ScienceOnline from data in International Coral Reef Initiative / NOAA Coral Reef Watch, 23 April 2025.

References
Carroll A.R., Copp B.R., Grkovic T., Keyzers R.A., Prinsep M.R., «Marine natural products», Natural Product Reports, 42(2), 257–297, 6 February 2025, open access CC BY-NC 4.0. doi: 10.1039/d4np00067f
Mayer A.M.S., Mayer V.A., Swanson-Mungerson M., Pierce M.L., Roberts C.M., Rodríguez A.D., Nakamura F., Taglialatela-Scafati O., «Marine Pharmacology in 2022–2023: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis and Antiviral Activities, Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action», Marine Drugs, 24(4), 133, 9 April 2026, open access CC BY. doi: 10.3390/md24040133
Newman D.J., Cragg G.M., «Marine Natural Products with Pharmacological Properties», in Puglisi M.P., Becerro M.A. (eds), Chemical Ecology. The Ecological Impacts of Marine Natural Products, CRC Press, Boca Raton, 2019, pp. 1–48.
Lavergne V., Harliwong I., Jones A., Miller D., Taft R.J., Alewood P.F., «Optimized deep-targeted proteotranscriptomic profiling reveals unexplored Conus toxin diversity and novel cysteine frameworks», Proceedings of the National Academy of Sciences, 112(29), E3782–E3791, 2015. doi: 10.1073/pnas.1501334112
IUCN, «From desert frog to deep-sea molluscs, remarkable species at risk – IUCN Red List», press release, Gland, 9 July 2026. https://iucn.org/press-release/202607/desert-frog-deep-sea-molluscs-remarkable-species-risk-iucn-red-list
IUCN, «Over 40% of coral species face extinction – IUCN Red List», press release, Baku, 13 November 2024. https://iucn.org/press-release/202411/over-40-coral-species-face-extinction-iucn-red-list
International Coral Reef Initiative, «84% of the world’s coral reefs impacted in the most intense global coral bleaching event ever», 23 April 2025. https://icriforum.org/4gbe-2025/
Marine Pharmacology, «Approved Marine Drugs», updated 9 April 2026, accessed 13 September 2026. https://www.marinepharmacology.org/approved
Royal Society of Chemistry, MarinLit. A database of the marine natural products literature. https://marinlit.rsc.org
Donati G., Porfirio B., «Prospects», in «Marine Pharmacology & Toxicology», The Shell, 174–175, 21, 1983; Italian edition: «Prospettive», in «Farmacologia e Tossicologia Marina», La Conchiglia, 174–175, 21, 1983.
Donati G., Porfirio B., «Antineoplastic Substances from the Sea. Part II», in «Marine Pharmacology & Toxicology», The Shell, 182–183, 27, 1984; Italian edition: «Sostanze antineoplastiche dal mare. Parte II», in «Farmacologia e Tossicologia Marina», La Conchiglia, 182–183, 27, 1984.