Cleaner fish may spread helpful microbes across coral reefs

Where do fish go for a deep clean? Coral reefs. These underwater hubs host bustling stations where small fish perform hygiene services for their larger neighbors.

Cleaner fish dart around bigger “clients,” even entering mouths to remove parasites and bacteria. Some even offer what looks like a massage.

But are these fish spas just about grooming? Or could they affect the entire microbial network of a reef?

Cleaner fish help microbes travel

A study published in the journal Marine Ecology Progress Series explores this hidden layer of reef life. The research was led by experts at the University of California, Davis and Woods Hole Oceanographic Institute (WHOI).

The team set out to investigate whether cleaner stations help spread harmful pathogens or helpful microbes.

If microbes move easily around a reef, they may influence coral bleaching or disease resistance. Understanding these interactions could inform coral restoration strategies.

“How pathogens or microbes are moving around a reef could be critically important to understanding how individuals will be affected,” said lead author Anya Brown, an assistant professor with the UC Davis Bodega Marine Laboratory and a National Geographic Explorer.

“We know microbes play a role in coral bleaching, for example. This study really lays a foundation for using cleaner fish stations as a way to study movement of microbes around the reef environment.”

Cleaner gobies and fish visits 

The scientists chose to study the cleaning goby, a tiny fish known for its services on Caribbean reefs. Despite its small size, the goby plays a key role in reef life. It has a striped body and is about the size of a human pinky finger.

In June 2021, the researchers removed these gobies from some cleaning stations on reefs in Puerto Rico and St. Croix. They wanted to see what would happen when these little cleaners were taken out of the picture.

The team analyzed changes in water quality, shifts in the kinds of microbes in the water, and how other fish, especially damselfish, responded. Damselfish often visit gobies to get cleaned.

The results were revealing. Places that still had gobies attracted more fish. These active cleaning spots seemed to influence the tiny life forms in the water too. But each reef reacted differently, showing that microbial shifts depend on local reef conditions.

Impacts beyond parasite removal

Cleaner fish do more than just remove parasites from other fish. Their cleaning activity may also change the types and amounts of microbes in the reef.

By interacting closely with many fish, cleaner fish might help spread certain microbes or reduce harmful ones. This can affect not only the health of individual fish but also the balance of microscopic life across the reef. So, their impact extends beyond visible cleaning – it reaches the invisible microbial world that supports the whole ecosystem.

Study co-author Paul Sikkel is a research professor at the Rosenstiel School’s Department of Marine Biology and Ecology.

“While larger organisms on coral reefs attract the most attention, the study underscores the huge impact tiny organisms such as these fish can have and how important they are to helping healthy reef ecosystems function,” said Sikkel.

“While cleaner fish are well-known for their role in consuming parasites and reducing stress in other fish, this is the first field study to quantify their effects on microbes of other fish and the surrounding coral reef environment.”

Global collaboration and next steps

Scientists from several institutions collaborated on the research, including Amy Apprill and Jeanne Bloomberg from WHOI, and Gina Hendrick and Matthew Nicholson from the University of Miami. Marta Soares and Raquel Xavier joined from the University of Porto in Portugal.

The study was supported by major science organizations. Funding came from the National Science Foundation, WHOI, and Portugal’s Foundation for Science and Technology.

Even though cleaner fish are tiny, they can influence entire ecosystems. Researchers are just beginning to understand how these fish help control the movement of microbes and maintain reef balance. The study opens new questions about the deeper connections shaping ocean life.

The study is published in the journal Marine Ecology Progress Series.

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