Anemones are friends to fish



IMAGE: An orange and white clownfish lurks from the folds of a mostly red anemone to see if predatory sea creatures are hunting for food in the form of clown fish. Researchers at UD …
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Credit: Photo of Stefan Andrews

When predators hunt small reef fish in the ocean, many of these small fish do the same thing: they hide in a nearby anemone.

New research from the University of Delaware, however, shows that large fish also associate with anemones. The difference is that large fish associate with anemones as juveniles, while smaller species associate with anemones throughout their lives.

This mutualistic relationship, in which individuals of two or more species cooperate, is driven by predation. Predators tend to attack smaller fish, which in turn, associate more with anemones for protection. While the benefit to fish is protection from predators, anemones have access to nutrition and increase aeration by hosting and protecting these small reef fish.

"Being able to understand why this relationship evolved can tell us more about reef ecosystems as a whole," said Lane Johnston, who graduated in 2018 with a master's degree in marine behavioral ecology and worked on the study during his time at the University. "Our finding was that predation and the attempt to avoid predation is really what drives the relationship, and that can help us understand how population dynamics change in a reef or any advancing ecosystem."

The research was recently published in the Ecology Letters Scientific Journal.

Johnston conducted the study in Moorea, located in French Polynesia, with its mentor, Danielle Dixson, assistant professor at the School of Marine Sciences and Policies of the Faculty of Earth, Oceans and the Environment; William Feeney, now a postdoctoral researcher at the University of Queensland in Australia who worked as a Fulbright Fellow in Dixson's lab during the study, and Rohan Brooker, now a researcher at Deakin University in Australia who was a postdoctoral researcher at Dixson & # 39; ;s. during the study.

From January to February 2016, researchers collected anemones and corals as well as threespot dascyllus – a fish they chose to be a case study subject which is a mutualistic anemone – on snorkel and scuba dives to conduct a study of laboratory with a field study on the shallow reef plains at Tema Bay.

They selected the fish-maiden as a kind of locally abundant and non-anemone comparison for the dascyllus to three, and classified the maidenfish and the dascyllus into four size categories:

    Rookie – less than 2 inches in size;

    Juvenile – 2 to 4 centimeters in size;

    Small adults – 4 to 6 centimeters in size; and

    Great adults – larger than 6 centimeters.

Arceye hawkfish, speckled sandperch and squirrelfish were selected as the predators in the study.

The purpose of these experiments was to verify whether the size of the dascyllus body could explain patterns of anemone associations among individuals under natural conditions, whether smaller fish were more vulnerable to predation by the three predators compared to their larger pairs and whether associations with anemones provided more protection than coral shelter.

The field study revealed that recruitment and juvenile dascyllus are associated almost exclusively with anemones, whereas the use of anemone progressively diminished between the small adults and the large adult dacyllus.

They also found no preference among predators for body size and dascyllus, and if anemones were available, they would help dascyllus to survive predation better than coral.

"It's kind of intuitive.If smaller fish can not be protected from predators, they need to find a habitat that can help protect them when they are smaller," Johnston said. "Makes sense [that they’d use anemones]and we just needed to prove it. "

In addition to the field and laboratory studies, collaborators in Australia, France and the United Kingdom followed field results to determine the evolutionary history behind the use of anemone.

Using large datasets from sites such as, a global database of fish species, these researchers found that mutualisms between fish and anemones evolved on at least 55 occasions in 16 fish families in the last 60 million years . In addition, they also found that larger body species associated with anemones as juveniles, while species of smaller bodies associate with anemones throughout their lives.

Johnston said it was interesting to discover that many species of fish associate with anemones, since they were once linked to only a handful of fish species, as the titular hero of the film, Finding Nemo.


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