Coral venom and toxins as protection against crown-of-thorns sea star attack

Crown-of-thorns sea star (CoTS) outbreaks are one of the leading causes of hard coral cover decline across the Indo-Pacific, posing a major threat to the health and resilience of coral reefs. However, the drivers underlying feeding on preferred (e.g., Acropora spp.) versus non-preferred (e.g., Porites spp.) are poorly understood. We hypothesised that coral venom may influence CoTS food preferences. We investigated whether coral venom toxin and peptide families may drive CoTS prey preferences by comparing the genomes and transcriptomes of preferred (five Acropora species) and non-preferred (five Porites species and Echinopora lamellosa) prey species of CoTS. We constructed databases of known cnidarian venom toxins, and along with the full UniProtKB/Swiss-Prot Tox-Prot database, used these to identify toxin peptides and investigate function and phylogeny. The most abundant toxins across all coral species included kunitz-type neurotoxins, neurotoxic turripeptides, snake venom lectins, toxic proteases and actinoporins. There were proteins present only in certain Porites species but completely absent from all Acropora species (e.g., tereporin/conoporin, snake venom peptides) and vice versa (e.g., sarafotoxin). Further, Porites species contained a homolog to conkunitzin, a toxin known to disintegrate the tube feet of CoTS, suggesting a potential mechanism for their lower susceptibility to predation. We also observed a greater diversity of jellyfish-like proteins in CoTS-exposed Porites species compared to naive Porites species, suggesting these proteins deter CoTS. These findings have direct applications to assessing reef corals susceptibility to future CoTS outbreaks and active reef management.