The damselflies have been found to disrupt “cleaning services” vital to reef health. And climate change may mean it will only get worse.
The meal of choice for the Caribbean cleaner fish, the shark-nosed goby, is a platter of parasites, dead tissue, scales and mucus taken from the bodies of other fish. By removing these pieces, the gobies offer their “cleaning services” to other marine species – a famous example of a mutually beneficial relationship between species.
But new research from Cambridge University and Cardiff University shows that when gobies inadvertently take up residence in the territories of aggressive damselfish, the damselfish scares off the gobies’ ‘difficult customers’.
The study, published today in Behavioral ecology, is an example of a largely unexplored phenomenon: a mutually beneficial relationship in nature disrupted by a third party.
Shark-nosed gobies work alone or group together and set up a “cleaning station”: a fixed location in a particular nook of the coral reef, where other parasite-ridden marine species go to take advantage of the gobies’ food needs. .
“The gobies wait at cleaning stations that customers visit, such as in stores. And with customers come parasites,” said Dr Katie Dunkley, a behavioral ecologist in the University of Cambridge’s Department of Zoology. “In exchange for a cleaning service, the gobies receive payment in food. »
Clients are varied and include parrotfish, surgeonfish, and butterflyfish. These discerning customers do their shopping, visiting various cleaning stations open for business. If interested, they will adopt a stationary pose which makes cleaning more likely – usually a head or tail position with all fins flared out.
During a cleanse – which can last from a few seconds to several minutes – the gobies make physical contact with the client, removing parasites and other tissue from the corpse. It’s called “tactile stimulation,” and in addition to getting rid of parasites, it can act as a stress-reducing massage for the client, Dunkley explains. Previous research has established the importance of cleaners – their removal has led to a decrease in the number and variety of fish species on reefs.
“Cleaning stations act like a marketplace, and if customers stop showing up, over time a cleaning station is going to close,” Dunkley said.
Five researchers spent more than 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-minute periods from 8 a.m. to 5:15 p.m. each day.
They found that client fish were less likely to go to cleaning stations that were more often patrolled by damselfish, which scared off “intruders”.
“I thought the damsels might also play a role when they visit the cleaning stations – although they are not cleaned often – but to see just their influence was surprising.
“The damselflies act like farmers by removing the algae they don’t want, to encourage the growth of their favorite algae. Damselfish protect their algal territories, and these antisocial fish spend a lot of time patrolling their territories, scaring off intruders by biting them. , attacking, chasing or threatening parries. »
Damselfly territories cover up to 70% of some reefs. On a healthy coral reef, a balance is maintained between algae and coral. But as reefs deteriorate and overfishing intensifies, algae thrive. As reefs deteriorate, damselflies can become more common and/or aggressive, reducing the number of species receiving the goby-cleaning treatment needed to keep them healthy, Dunkley says. This might ultimately contribute to the degradation of the delicate reef-supported ecosystems.
“In the future, we would like to find out the motivations of the ladies. Are they motivated by the desire to protect their algae farms or monopolize the cleaning stations? said Dunkley, Charles Darwin Fund and Galapagos Islands Junior Fellow at Christ’s College, Cambridge.
“Just as humans are connected through family, friends and colleagues, all fish are connected to each other. It’s important that we don’t just look at relationships in isolated bubbles. We need to step back and see how all fish are connected so that we can protect ecosystems like coral reefs. »
The study was funded by a GW4+ scholarship from the Natural Environment Research Council and Christ’s College University of Cambridge Galapagos Islands Fund (both awarded to first author, Katie Dunkley). The final author, James Herbert-Read, was supported by the Whitten Lectureship in Marine Biology and a grant from the Swedish Research Council (2018-04076).
