“Anti-social” damselfish deter cleaner fish customers, which could contribute to coral reef collapse

Damselfish have been discovered to be disrupting ‘cleaning services’ that are vital to reef health, and climate change may mean this is likely to only get worse.

The preferred meal for the Caribbean cleaner fish, the sharknose goby, is a slab of parasites, dead tissue, scales, and mucus stabbed from the bodies of other fish. By removing these morsels, gobies offer their ‘cleaning services’ to other marine life – a famous example of a mutually beneficial relationship between species.

But new research from the University of Cambridge and Cardiff University shows that damselfish scare off gobies’ “picky customers” when they accidentally set up shop in the territories of aggressive damselfish.

The study published today in behavioral ecologyis an example of a largely unexplored phenomenon: a mutually beneficial relationship in nature disrupted by a third party.

Working alone or in groups, sharknose gobies set up a “cleaning station,” a permanent location in a designated corner of the coral reef where other parasitized marine life can go to exploit the gobies’ nutritional needs.

“Gobies wait for customers at cleaning stations, much like they do in stores. And with the customers come the parasites,” said Dr. Katie Dunkley, behavioral ecologist in the Department of Zoology at the University of Cambridge. “The gobies receive food in exchange for cleaning.”

Customers are diverse and include parrot fish, surgeon fish and butterfly fish. These picky customers fish around and visit various cleaning stations that are open for business. When interested, they assume a stationary pose that makes cleaning more likely – typically a head or tailstand position with fins flared.

During a cleaning, which can last from a few seconds to several minutes, gobies make physical contact with the client and remove parasites and other dead body tissue. This is called “tactile stimulation,” and not only can it get rid of parasites, but it can also act as a massage and reduce the client’s stress, Dunkley says. Previous research has demonstrated the importance of cleaners – removing them resulted in fewer numbers and less variety of fish species on the reefs.

“Cleaning stations act as a marketplace, and if the customers stop showing up, over time a cleaning station will go out of business,” Dunkley said.

Five researchers spent over 34 hours observing cleaning stations on a shallow fringing reef in Tobago over a six-week period. Equipped with snorkels and waterproof paper, they recorded underwater interactions for 10 minutes each day from 8:00 a.m. to 5:15 p.m.

They found that customer fish were less likely to go to cleaning stations, which were more frequently patrolled by damselfish, which deterred “invaders.”

“I thought damselfish might also play a role when they visit cleaning stations – although they’re not often cleaned – but to see how influential they have been was startling.

Damselfish behave like farmers, weeding out algae they don’t want to encourage the growth of their favorite algae. Damselfish protect their algal areas, and these antisocial fish spend much of their time patrolling their territories, deterring intruders by biting, attacking, chasing, or threatening.”

The territories of some damselfish cover up to 70% of some reefs. On a healthy coral reef, a balance between algae and coral is maintained. But as reefs deteriorate and overfishing increases, algae thrive. As reefs deteriorate, damselfish can become more common and/or more aggressive — resulting in fewer species getting the goby cleaning treatment necessary to keep them healthy, Dunkley says. This could ultimately contribute to the collapse of delicate ecosystems supported by reefs.

“In the future we would like to tease out the motives of the damselfish. Do they want to protect their seaweed farms or monopolize cleaning stations?” said Dunkley, a junior research fellow with the Charles Darwin and Galapagos Islands Fund at Christ’s College, Cambridge.

“Just as humans are connected through family, friends and co-workers, all fish are connected. It’s important that we don’t just look at relationships in isolated bubbles. We need to take a step back and see how all fish are connected and we can protect ecosystems like coral reefs.”