We have come to think of a coral not as a single organism but as a holobiont: a coral animal, its photosynthetic algae, and a broader cast of fishes and invertebrates that live in and around its branches. Much of the recent excitement about these partnerships has focused on how they help corals cope with slow, large-scale stressors like warming and bleaching. But corals also face a more immediate hazard: physical injury from predators, storms, and handling. A wound that fails to close can be overgrown by algae or invaded by pathogens, threatening the whole colony. Whether the fishes living inside a coral help it heal those wounds had gone almost entirely untested. Led by Hayden Vega, and working with Craig Osenberg, Ashley Seifert, Ninah Munk, and me, we set out to find out. At the Gump Station in Mo'orea, French Polynesia, we ran a controlled experiment on the branching coral Pocillopora, one of the most common reef-builders in the lagoon and a favorite home of the yellowtail damselfish, Dascyllus flavicaudus. We cut 72 coral fragments to a standard size, then gave them either no wound, a small wound, or a large wound. Half the tanks housed a group of damselfish; the other half had none. Every coral received the same food and light. Then, for three weeks, we photographed the wounds and watched them close. The fish made a striking difference, and the difference grew with the size of the injury. For small wounds, corals living with damselfish healed about 38% faster than corals without them. For large wounds, the effect was even larger: healing rates jumped by 55%, so that wounded corals with fish closed their injuries roughly twice as fast as those without. By the end of the experiment, most of the wounds on corals with fish had fully closed, while most of the wounds on corals without fish were still open. Because our clock stopped at 21 days, we almost certainly underestimated how much the fish helped. Healing was not the only thing that suffered when fish were absent. We also measured photosynthetic efficiency, a gauge of how well the coral's algal symbionts were working. In corals with damselfish, that efficiency stayed high regardless of how badly the coral had been wounded. In corals without fish, it fell steadily as wounds got larger. Turf algae told the same story: colonizing algae took hold on wounds about nine times more often when fish were absent, exactly where a coral can least afford the competition. Interestingly, the fish did not measurably change how much new skeleton the corals laid down. Their benefit was concentrated in tissue repair and symbiont performance. Why would a resident fish speed a coral's recovery? Several mechanisms likely act together. Damselfish excrete ammonium-rich waste that fertilizes the coral's algae, supplying the extra energy that rebuilding tissue demands. Their constant movement through the branches, especially at night when oxygen runs low and the metabolic cost of healing is high, stirs water and delivers oxygen. And by keeping wounds from being smothered by algae, they buy the coral time to close them. Together, these findings add tissue repair to the growing list of ways coral-associated fishes support reef resilience, alongside their known roles in coral growth and heat tolerance. Protecting these everyday partnerships may be as important for reef recovery as protecting the corals themselves.
Citation
Vega, Hayden; Osenberg, Craig W.; Seifert, Ashley W.; Munk, Ninah; Stier, Adrian C. (2026). Coral-associated fishes accelerate coral wound healing and photosynthetic recovery. Biology Letters.
"The fish made a striking difference, and the difference grew with the size of the injury."
This paper is Open Access.
Watch the wounds close
Coral fragments were given a small or large wound and kept with or without yellowtail damselfish for three weeks. Pick a wound size and press play to see each coral heal at the rate measured in the experiment.
Rates from Vega, Osenberg, Seifert, Munk & Stier (2026), Biology Letters (Results, Fig. 2), drawn to scale on a 3 × 4 cm fragment. The animation assumes each coral healed at its average rate. The paper notes that this underestimates healing for wounds that closed before day 21, so the real fish effect is probably larger.
Every coral, one dot
Averages hide the individual corals. Each dot is one wounded fragment, placed by how much of its wound had healed by day 21. Corals whose wounds closed completely gather in the shaded zone on the right.
Tap or hover a dot to see that coral.
Per-fragment measurements from the public data repository for Vega, Osenberg, Seifert, Munk & Stier (2026), Biology Letters. One fragment without fish whose wound grew larger is not shown; with it removed, the closure counts match the paper (16 of 24 with fish, 9 of 23 without).
Closed is not the same as healthy
A closed wound still has to work. The team measured how efficiently the newly grown tissue photosynthesized (Fv/Fm, the maximum efficiency of photosystem II). Step through to compare corals without and with damselfish.
Means and 95% confidence intervals from Vega, Osenberg, Seifert, Munk & Stier (2026), Biology Letters (Results, Fig. 3B). Small dots are individual fragments from the paper's public data repository. The y-axis starts at 0.54 to show differences that are small in absolute terms.
Who claims an open wound
Bare coral skeleton is open real estate. During healing, turf algae often moved into the wounds. Press the button to see which corals still had algae on their wounds at day 21.
From Vega, Osenberg, Seifert, Munk & Stier (2026), Biology Letters (Results). Each square is one wounded fragment; algal status for each fragment comes from the paper's public data repository.
Cite this article
Vega et al. (2026). Coral-Associated Fish Accelerate Coral Wound Healing. Ocean Recoveries Lab. https://doi.org/10.1098/rsbl.2026.0177
