The relationship between clownfish and anemones is one of the most recognizable forms of marine mutualism. With that said, how clownfish managed to befriend the dangerous, carnivorous anemone reveals interesting facts about both sea creatures.
Clownfish are immune to anemones due to an external layer of mucus. This layer protects clownfish from the stinging tentacles of anemones. There’s also a lot of microbial sharing between the two. This explains why anemones don’t bother eating clownfish, since they share bacteria.
Because there is a great deal of research regarding what clownfish get out of the relationship, not a lot is known about how clownfish help anemones. A closer look gives us insight into how crucial clownfish are in the lives of the flowers of the sea.
Why Don’t Anemones Sting Clownfish?
Clownfish avoid getting stung by anemones thanks to a coat of mucus that makes them invulnerable to the stings. Because of this mucus layer, clownfish can live in sea anemones without getting hurt.
Anemones are living animals that need to eat and protect themselves. Like all living creatures, anemones have defense mechanisms in place to ward off predators. One of the many ways sea anemones defend themselves is with harpoon-like stingers called nematocysts, located in their tentacles.
They sting any fish that comes near, paralyzing them to make them easier to capture and eat. Anemones are carnivorous, so they are very dangerous to any fish that comes in contact with them.
So, how is it that clownfish aren’t affected by the nematocyst? Clownfish are born with a protective mucus layer. Most fish have a similar protective layer (which is why they’re always so slimy), but clownfish have a mucus layer that is thicker than that of other fish. According to the Royal Society, clownfish are born with this protective mucus layer, but it thickens when they come into contact with anemones.
Why Don’t Anemones Eat Clownfish?
Anemones don’t eat clownfish because they don’t consider clownfish to be invasive. Other fish see anemones as potential food, which is why they swim towards the tentacles despite the danger. The anemone will paralyze and poison the attacking fish with its nematocysts to protect itself from being eaten. Because anemones are carnivorous and they need to eat, they will take advantage of the fish’s paralysis and eat it.
Even though clownfish sometimes nibble on anemone tentacles, the anemones don’t attack because they don’t see it as a threat. Even if they try to attack the clownfish, the protective layer of mucus makes clownfish invulnerable to the nematocysts.
Experts believe that the reason clownfish don’t feel the need to eat anemone is because of shared bacteria. It was once believed that direct contact was all that was needed for a clownfish and anemone to exchange bacteria as they acclimate to each other. However, researchers at Laval University demonstrated how the microbiome of a clownfish changes even without direct contact with an anemone.
This could mean that by being in proximity to anemones, young clownfish can acclimate to the anemone before it even comes into contact. This chemical change in the microbiome can signal one of two things to a clownfish that the anemone:
- Would not make good food
- Can offer protection
Whichever it is, it allows the clownfish to approach the anemone and begin hosting it. Once this process starts, the anemone doesn’t see the clownfish as a dangerous being due to the shared bacteria.
How Do Sea Anemones Benefit from Clownfish?
Sea anemones heavily rely on clownfish. Clownfish defend anemones from other fish, help them get sunlight exposure, and provide them with fertilizer. Even though anemones have effective ways to defend against other fish, they are still at risk of getting eaten. Sea stars, snails, and butterflyfish regularly consume anemone tentacles. If the anemone isn’t healthy or has had most of its tentacles damaged by fish, it won’t be able to sting an attacking fish properly.
When fish see that the anemone is hosted by a clownfish, they will most likely retreat. Clownfish are territorial to an almost ridiculous degree. They have enough moxie in their tiny bodies to bite human divers that get close to their anemones. No matter how big the intruder is, they will show aggression when it’s time to defend their home, which the anemones appreciate greatly.
Seaweed grows tall and proud all around sea anemones. This is a problem because the seaweed creates shade and blocks sunlight. Anemones need sunlight to stay healthy. Without proper lighting conditions, they die.
Even though anemones can move and swim, if the seaweed density is too great, they will have trouble relocating to an area with more sunlight. Clownfish eat the seaweed that grows around anemones and ensure that there is always enough sunlight.
Last but not least, clownfish provide anemones with fertilizer. Because the clownfish often scare other fish away, the anemones need to find another way to eat. Clownfish defecate around the anemone and provide it with nutrients that help the sea creature grow.
How Do Clownfish Benefit from Sea Anemones?
Sea anemones help clownfish survive by providing shelter and food. Although clownfish are highly territorial, no amount of aggression can protect them from larger sea creatures. From an evolutionary standpoint, it’s also inconvenient to fight for your life every other day. So, like most creatures, clownfish seek shelter to protect themselves and their eggs.
Because of their tentacles, anemones make great homes for clownfish. If any dangerous fish try to get near, they will get stung and poisoned by the anemone. This brings us to another advantage anemones provide clownfish: food.
Clownfish have various ways of eating from the anemone. One way is by eating anything that is left over from any fish that get devoured by the anemone. Another way is by nibbling on the anemone tentacles. Because of the shared microbiome, the anemones don’t consider this to be threatening.
Why Do Clownfish Rub Against Anemones?
Clownfish rub themselves against anemones as part of the pairing process. It means that the clownfish and anemone are getting to know each other and preparing for a long, beneficial relationship together.
Before a clownfish hosts anemone, it isn’t always ready to live in it. Although clownfish have a protective mucus that is thicker than the average fish, they still need to thicken it more in preparation for living in an anemone full-time.
Rubbing against anemones causes a chemical reaction that helps thicken the protective mucus layer. It also helps the anemone get used to the clownfish and see it as less of a threat. Think of it like two dogs sniffing each other as a way to get to know each other better.
According to the Georgia Institute of Technology, the effects of rubbing against an anemone are not permanent for a clownfish. Upon being separated from the anemone, the microbiome of clownfish resembled that of non-hosting fish.
Are Clownfish Immune to Jellyfish?
Clownfish are not immune to jellyfish stings. They may be slightly more resistant to it than other fish, but they can still get hurt and die if shocked by jellyfish.
The reason clownfish are immune to anemone stings and not jellyfish stings is because jellyfish stings are a lot stronger. Anemone stings can hurt, but the sensation can range from a small pinch to a mild burn. Jellyfish stings, on the other hand, can be much more severe.
Not all jellyfish stings are fatal. Some can be just as mild as anemone stings. However, there are some jellyfish species capable of distributing serious damage—enough to leave adult humans sore and sick for days.
The good news is that clownfish rarely stray far from home, so the chances of one getting stung by a jellyfish are rare. Experts theorize that clownfish can become resistant to jellyfish if they have the chance to acclimate to them as they would anemones. With that said, given how convenient the clownfish-anemone relationship is, experts doubt that clownfish will ever need to rely on jellyfish for survival.
Are Clownfish and Anemone Relationships Mutualism or Commensalism?
The relationship between clownfish and anemones is considered mutualism. Mutualism is when two species form a relationship where both can benefit from each other. The relationship between clownfish and sea anemones is considered to be one of the best cases of mutualism between marine animals. This is because both creatures benefit from each other in very clear ways and acclimate to each other quickly and without problems.
Clownfish and anemone relationships cannot be considered commensalism. Commensalism is a symbiotic relationship in which only one species benefits while the other is not affected or harmed. It is a completely one-sided relationship, which isn’t the case for clownfish and anemones, given how co-dependent they are on one another.
A good example of commensalism between marine creatures is the relationship between remora (suckerfish) and large sea creatures. Remoras cling to the bodies of sharks, whales, and turtles. They use the bigger animals to move around and protect themselves from predators by associating with bigger animals. This relationship is considered commensalism because the whales and sharks don’t need the remora to survive.
