Corals are borrowing a toxic trick from jellyfish to fend off their spiny predators.
Some coral reefs appear to have evolved venom components similar to those in jellyfish, potentially helping them discourage devastating attacks from crown-of-thorns sea stars, researchers report in Molecular Ecology. By comparing the genetic blueprints of corals that these sea stars love to eat versus those they avoid, scientists uncovered key differences in their toxin arsenals that might explain feeding preferences and offer clues for protecting reefs.
“We found genera-specific differences with jellyfish toxins (CFXs) only present in Porites species,” the researchers note in the study.
Crown-of-thorns sea stars, or CoTS, are voracious coral eaters scattered across the Indo-Pacific, where they can explode in numbers during outbreaks, stripping reefs bare and worsening damage from events like bleaching. At low levels, these sea stars are helpful, munching on fast-growing corals like Acropora to make room for slower ones like Porites. But in booms, a single star can devour up to 12 square meters of coral a year, and swarms race across reefs at 60 kilometers annually, slashing coral cover by half or more.
They gobble Acropora eagerly but snub Porites, even when options are slim. Past ideas pointed to nutrition, shape, or guardian critters on corals. But now a fresh angle has emerged: venom. Corals, like other stinging sea creatures, pack toxins in their nematocysts — tiny harpoon-like cells — to zap threats. To test this hypothesis, the team explored genomes from four Acropora species (preferred prey) and four Porites (avoided), plus one each from the Caribbean, where CoTS don’t roam, for comparison.
Across all, the toxin lineup featured neurotoxins to stun nerves and pore-forming toxins to punch holes in cells. But standout contrasts popped up. Porites alone carried homologues to CFX toxins, potent weapons from box jellyfish that can cause heart issues or cell breakdown. These are grouped with a specific jellyfish type known for cardio effects. Meanwhile, only Acropora had pore-formers with an aerolysin twist, a domain linked to bacterial toxins that rip open cells.
Geography mattered too. Certain toxin versions, like MAC-PF hole-punchers and those CFX-like ones in Porites, showed signs of rapid evolution, positive selection, in Indo-Pacific corals facing CoTS, but not in Caribbean ones safe from them. This hints that predator pressure shapes these defenses over time.
The work doesn’t prove these toxins directly repel sea stars, but it spotlights how corals might arm themselves differently. One Porites species boasted the most diverse toxin mix, perhaps explaining its low appeal to CoTS. Intriguingly, young sea stars start on algae before switching to coral, and bigger ones tolerate more venom, suggesting experience builds resistance.
“These findings suggest that, despite similarities in the overall toxin repertoire, there are distinct molecular signatures that may influence CoTS feeding behaviour,” the team adds.
Citations
L. M. Gorman et al. Coral Venom and Toxins As Protection Against Crown-of-Thorns Sea Star Attack. Molecular Ecology. Published online December 16, 2025. DOI: 10.1111/mec.70202
