These leather corals produce over 600 different chemical compounds to deter predators and competitors. Chemists study them for pharmaceutical leads, several show anti-cancer and anti-inflammatory properties.
Toby Hudson, CC BY-SA 3.0, via Wikimedia Commons
A chemical arms race on the reef
Unlike their stony relatives, soft corals lack a formidable calcium carbonate skeleton for defense. To survive in the competitive reef environment, they deploy a sophisticated chemical arsenal. Sessile and exposed, soft corals like the leather corals (Sarcophyton) and Sinularia species produce a diverse array of secondary metabolites, primarily terpenes and steroids. These compounds are not involved in primary life functions like growth but are instead used for protection.
This chemical warfare, known as allelopathy, has two main purposes. First, it deters predation from corallivorous fish and other marine animals. The chemicals make the coral tissue unpalatable or toxic. Second, these compounds are released into the water to inhibit the growth of nearby competitors, especially faster-growing stony corals. By creating a toxic zone, soft corals can secure their access to space and sunlight. Genera like Sarcophyton and Sinularia are particularly known for their potent chemical defenses, which can cause tissue death in stony corals that grow too close.
From coral defense to cancer treatment
The same potent chemicals that protect soft corals on the reef are of great interest to medical researchers. Soft corals are a source of thousands of compounds with potential as antibiotics, anti-inflammatory agents, and anti-cancer therapies. One of the most promising is a compound called eleutherobin, first discovered in the 1990s in a rare Australian soft coral. Laboratory studies showed that eleutherobin is a powerful inhibitor of cancer cell growth because it disrupts the cytoskeleton, an important structural component within cells. For decades, research was stalled because the original source was too rare to harvest for drug development. Recently, scientists discovered that common soft corals also produce it and have successfully identified the genetic code responsible, opening the door to lab synthesis.
Another significant compound is sarcophine, a cembranoid diterpene isolated in large quantities from Sarcophyton leather corals. Sarcophine and its derivatives have demonstrated the ability to inhibit tumor formation and have shown anti-inflammatory properties. Researchers have also modified sarcophine to create sarcodiol, which shows promising chemopreventive effects against melanoma cells in laboratory studies. The biodiversity of reefs in places like Fiji makes them hotspots for discovering new natural products with pharmaceutical potential.
💡Fun Facts
The compound eleutherobin stops cancer cells from dividing in a similar way to the well-known chemotherapy drug Taxol.
Some soft corals can release toxins that make up to 50% of the coral's dry weight.
Certain soft corals, like *Sinularia flexibilis*, can release chemicals that specifically inhibit the ability of stony corals to build their calcium skeletons.
When stressed or as a way to clean themselves, leather corals can retract their polyps and shed a waxy, toxic layer of mucus.
