Evidence of novel symbiotic relationships between Christmas tree worms and coral reef blennies and gobies

Morgan F. Bennett-Smith, Catheline Y.M. Froehlich, Lili F. Vizer, Peter M. Buston (2025). Symbiosis https://doi.org/10.1007/s13199-025-01067

In Kimbe Bay, Papua New Guinea, I set out to investigate a curious behavior I’d noticed during years of diving: occasionally, a small reef fish would perch directly on top of a Christmas tree worm—or even nestle within its delicate feeding structures. If you’ve seen these worms in the wild, you know they are famously skittish, disappearing instantly at the slightest disturbance. So why do some fish seem to get a free pass?

To explore this question, we spent several weeks observing patches of Porites coral inhabited by Christmas tree worms, recording every interaction between fish and worms. What we found was remarkable: certain species—particularly a small goby and a blenny—were regularly tolerated, while others triggered an immediate defensive retreat.

Is this a newly recognized mutualism? Or a subtle form of kleptoparasitism, where the fish cleverly exploit the worm’s feeding structure? Our paper dives into the details and explores what these surprising relationships might mean for life on the reef.

Link to paper: https://link.springer.com/article/10.1007/s13199-025-01067-w

Links to select press coverage:

BBC Wildlife Magazine: https://www.discoverwildlife.com/animal-facts/marine-animals/christmas-tree-worms-and-fish-papua-new-guinea