Divers and snorkelers alike may have had the opportunity to view anemonefish, also affectionately known as clownfish, in their natural habitat; but how many fully understand the complex association between these fish and their anemone homes? An astonishing symbiotic relationship exists between these two organisms, enabling the fish to enjoy a safe home, while the anemone is protected from predators and cleaned of parasites.
These parasites, which live off the tissues of the anemone, as well as leftovers from the anemone’s dinner, provide food for the fish and enable the fish to stay close to home rather than having to venture into the dark and dangerous open ocean for food. This relationship is described as mutualistic since both anemone and fish benefit. A pretty neat setup if you ask me!
By now you may be wondering how the anemones protect these little fish from the nasties that lurk in the shadows. Well, all anemones have characteristic stinging cells called nematocysts. These microscopic capsules contain very sharp barbs which are wrapped up tightly like a spring, ready to discharge and pierce prey at the slightest contact. You may have touched an anemone in a rock pool and felt the tentacles stick to your fingers. Those are the nematocyst barbs shooting into your skin, but don’t be alarmed, human skin is tough enough to prevent pain from this particular armament. However, jellyfish and bluebottles, which belong to the same group as anemones, have more vicious barbs which are laced with potent toxins, giving unfortunate swimmers and divers nasty stings if touched.
Given that anemones have such effective weaponry, how are clownfish not killed by the stings of their own hosts? This is a mystical marine conundrum which has not yet been solved. One opinion is that the mucus of the anemonefish protects them from the anemone stings; another is that the mucus lacks the proteins found in the mucus of most marine animals, allowing the clownfish to pass by the tentacles without being recognised as prey.
Of over one thousand species of sea anemones, only ten host clownfish. As there are twenty-eight different species of clownfish, not all fish prefer a specific anemone species. However, these fish are very territorial and refuse other species of clownfish to enter their home in fear of it being invaded. Clownfish are beautiful creatures, ranging from black to orange, all with striking white bars across their bodies. They are wonderful to photograph as they never wander far from their colourful homes, but be careful not to stress them out while observing their unusual behaviour.
Another remarkable behavioural characteristic of clownfish is the presence of a dominance hierarchy. The largest fish, typically being the only female, calls the shots and breeds with the largest of the males in the group. The rest of the clownfish, which are usually all males, are suppressed by the aggressive female and do not breed. Interestingly enough, all clownfish are male when they are born. It is only when the dominant female dies, that the next largest clownfish develops into a female!
Zooxanthellae, porcelain crabs and anemone shrimps are just a few more of the many intriguing symbionts that are associated with sea anemones on coral reefs. But that is another story for another time. Now, armed with all this fascinating information, look out for these two unique marine animals and appreciate the complexity that is the anemone-clownfish interaction.
By: Megan Laird