Accommodating Anemones: Housing more than just clownfish

Reference: Hayashi, Kina, et al. “Large host anemones can be shelters of a diverse assemblage of fish species, not just anemonefish.” Journal of Fish Biology (2021). Doi: 10.1111/jfb.14916

Clownfish Cover

The film Finding Nemo gave the world many insights into the lives of marine fishes, including the fact that clownfish live in sea anemones. Anemones are animals, not plants, and are closely related to corals. Many anemone species tend to live on or near coral reefs, and have soft tentacles that contain stinging cells. These stingers, while generally too small to hurt humans, can injure fishes or other animals that get too close to the anemone. This is an excellent defensive tool, because it is very unlikely that a predator will eat an anemone if the cost of the meal is intense stings. Clownfish use these stinging tentacles to their advantage: they acclimate themselves to an anemone by developing a layer of mucous over their bodies that makes them immune from the anemone’s stinging cells. After they gain this immunity, they are able to use the anemone as shelter, hiding from their own predators. The relationship between these two marine animals is a well-studied one, but over the years, scientists have noticed that other fishes have also been seen in and around anemones. Could it be that clownfish are not alone in their use of anemones? Researchers in Japan, from the University of Ryukyus, set out to find the answer.

Anemone Associations

Researchers examined two study sites in the East China Sea – the Sakishima Islands and the Okinawa Islands. The coast around the Sakishima Islands has many shallow reefs and small anemones, while the Okinawa Islands has slightly deeper reefs and larger anemones, so researchers were able to see if these differences affected how fish behaved. Over several months at each site, researchers noticed which species of fishes went near or inside anemones, what the fishes were doing, the size of the anemones, and if clownfish were present with other species.

A snapshot of a coral reef off the coast of the Okinawa Islands. These reefs are vibrant spaces that house many corals, fishes, and anemones. Photo by Ryukyu Islander.

It turns out that the size of the anemone had a lot to do with the likelihood of fishes interacting with it. The larger the anemone, the more likely clownfish, as well as other types of fishes, were to inhabit it. Since anemones near the Okinawa Islands were larger than those near the Sakishima Islands, this led to some differences between the two sites. In all, researchers found seven fish species other than clownfish near anemones at the Sakishima Islands, and 15 non-clownfish species near the Okinawa Islands. Additionally, if a clownfish chose an anemone, that anemone was more likely to have a high growth rate, possibly because the anemones can feed off the waste that clownfish produce.

Some fish species, such as the threespot dascyllus, a black damselfish with large white spots, will only inhabit anemones that do not have clownfish, likely because some clownfish species can be territorial and aggressive. Other fishes, such as cleaner wrasses, were more likely to be around anemones if clownfish were present. This is because cleaner wrasses will actually pick dead skin and mucous cells left by clownfish off the anemones. All of the non-clownfish species seen in this study did not actually touch the anemone tentacles – they swam between or underneath them. This indicates that these other fishes probably do not acquire immunity from the anemone stinging cells like clownfish do.

The bluestreak cleaner wrasse, one of the species found to interact with anemones at both study sites. These cleaner wrasses will pick clownfish mucous and dead skin cells off anemones, giving themselves an easy meal. Photo by Francois Libert.

Saving Sea Anemones

This study is an excellent example of how systems in the ocean can be very complex. Even a seemingly straightforward relationship like that of clownfish and anemones is not all it seems. Given that sea anemones are found mostly near coral reefs, and that these reefs are in danger of severe damage or destruction due to climate change and ocean acidification, anemones are in serious trouble. Hopefully, the information gleaned from this study can help inform organizations and governments that are trying to preserve coral reefs of the importance of anemones for not only clownfish, but many other fish species too. If you would like to learn more about sea anemones and their importance to coral reefs, you can check out National Geographic’s website here. To learn more about some of the work being done to protect coral reefs in general, head to the Coral Reef Alliance webpage.


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