Fish are helping corals heal faster, study finds

Corals share a close bond with the fish dwelling among them, and that relationship could be even stronger than previously known.

A new study published July 8 in Biology Letters found that the yellowtail dascyllus (Dascyllus flavicaudus), a type of damselfish, helps heal injuries on Pocillopora spp., a genus of stony coral found largely in the Indo-Pacific Ocean.”Surprisingly, we found that the bigger the wound, the faster the recovery,” said Hayden Vega, lead author and Ph.D. student at the University of California, Berkeley.

For the experiment, the team collected 72 corals of identical size from Mo’orea, French Polynesia, and divided them into small, large and “no wound” categories. One subset was observed with fish and another without for 21 days.

Corals with small wounds healed 38% faster in the presence of fish than those without. Among corals with larger wounds, healing was 55% faster with the fish.

Researchers also found that in the presence of damselfish, the photosynthetic efficiency of algae living within corals remained stable across wound sizes. Without fish, efficiency declined as wound size increased.

While the precise mechanism is not yet clear, Vega identified three possibilities: fish feces may supply nitrogen and phosphorus as fertilizer for coral’s algae, fish movement could increase water flow improving nutrient uptake, and fish may contribute directly to wound cleaning.

Previous research has shown coral-dwelling fish aid in cleaning wounds and help corals tolerate warming oceans. The new evidence adds another dimension.”These positive interactions between species under stress end up creating a network of resilience in ecosystems,” Vega told Mongabay.

Andrew Shantz, a marine ecologist at the University of Hawai’i who was not involved in the study, said the findings may be broadly applicable to damselfishes across the tropical Pacific, Indian Ocean and Great Barrier Reef, and could inform conservation.”Conservation plans could potentially be designed around preserving the habitat of these fish, as much as it is about corals,” he said.

Both corals and damselfish face rising threats from warming oceans, acidification, and collection for the aquarium trade.