Sea Anemone loving Damselfishes
In this article, I’m going to introduce you to the famous anemonefish, also called clownfish. The anemonefish belong to the same biological family as the damselfish, the family Pomacentridae, which is made up of 360 species. There are approximately 30 species of anemonefishes, who together form the biological subfamily Amphiprioninae. All anemonefish live in the Indo-Pacific and are always found in association with one of 10 different species of sea
anemones (each anemonefish species has its favorite sea anemones). As sea anemones need a lot of light, anemonefishes live in relatively shallow waters, usually not deeper than 15 meters (49 ft.). Clownfishes typically live in tropical seas, but a few species can be found in subtropical waters. Many anemonefishes have limited geographical ranges, due to the short larval stage, which takes just a few days (more about that later). However some species have huge geographical ranges. The Clark’s Anemonefish for instance, can be found as far north as the Miyake-Jima Island of Japan, as south as western Australia, as east as Melanesia and as west as the Persian Gulf. Clownfishes feed on zooplankton and algae, as well as tiny shrimps, crabs, worms, tunicate larvae, fish eggs and much more. They are opportunists, which means that they can adjust their diet anytime if circumstances require it.
Heroes and Cowards
The thirty species can be divided into two subgroups: The poor swimmers or cowards and the skilled swimmers or heroes. Poor swimmers have rounded tail fins and use primary their pectoral fins to move. They stay always very close to their host anemones and retreat into the tentacles as soon as they feel threatened. The Pink Anemonefish
(Amphiprion Perideraion), the Skunk Anemonefish (Amphiprion Akallopsisos), the saddleback anemonefish (Amphiprion polymnus), the Common Clownfish (Amphiprion Ocellaris, or simply “Nemo”) and the Percula clownfish (Amphiprion Percula) belong all to the coward group. The skilled swimmers on the other hand have more emarginated caudal fins, which allows them to move much faster. Their behavior is less defensive and they are more likely to attack intruders. They often swim a meter or more above their host anemone and sometimes leave their host anemone altogether for foraging. When far away from their host anemone and threatened, they often seek shelter in coral and rock crevices. Famous representatives of this group are the Clark’s Anemonefish (Amphiprion Clarkii) and the Orange-finned Anemonefish (Amphiprion Chrysopterus). These heroes aren’t afraid of anything and attack predators many times their body size. When divers encounter coward clownfishes, they usually disappear deep between the tentacles of their host sea anemone. The heroes on the other hand, come out of their hiding places and attack innocent divers often (fortunately they are too small to cause any serious harm to the diver).
Bossy females and “psychological castration”
Anemonefishes usually live in groups that consist of a single female, a smaller lucky sexually active male and several even smaller male juveniles or subadults, also called “non-breeders”. All Anemonefishes are primarily male, but are able to change to a female if the circumstances allow it. The smaller “non-breeders” are sexually inactive and miss fully developed male sex organs. The reason for their impotence is called “psychological castration”. Their growth
rate and sexual functional capabilities are repressed by the presences of the dominant adult pair. Through slowing down their growth rates and staying sexually inactive, they don’t become a threat to the bigger members above them and are able to avoid conflict and eviction from the host anemone (competitors are often chased away from their home and forced to seek a new host anemone). Only when the sexually active male or the big dominant female disappear are they able to develop to their full potential. The biggest fish in the group will always become a female, whereas the second biggest fish will be allowed to become a sexually active male. However, Anemonefishes are not damned to stay at their original host anemone all their life and wait their turn to transform into a female or active sexual male. They are able to emigrate to another sea anemone and join new groups. This emigrations are especially common with the anemonefishes of the hero or skilled swimmer group. Clark’s Anemonefish for instance, often emigrate to new places, chase competitors away and are thus able to transform into sexually active males or even bossy females.
Gender transformations aside, how is it possible anyway, that these fishes can live between the poisonous tentacles of sea anemones? The answer to this question isn’t fully understood yet, but there are some popular (and probably less popular) theories. One of the more famous theory believes that the mucus layer covering the fish’s body has a special biochemical composition providing protection from the anemone’s stinging cells (called “nematocysts”). Through this biochemical composition of their mucus layer, the anemone fails to recognize the fish as a food source and doesn’t fire its stinging cells. As there are different sea anemones, the fishes need to change their biochemical mucus layer once they change a sea anemone or once they return from a longer stay away from their original home. To do this, the anemonefish goes through an
elaborate dance ritual. First it uses only its ventral fins to touch the anemone’s tentacles gently, then it uses its entire belly to rub it against the tentacles. The acclimation dance can take several hours and only after the dance ritual is finished, the anemonefish is able to dive fully into the tentacles of its new host anemone, welcome home! Obviously the anemonefish benefit from the protection the anemone provides them, as most predators are afraid of the poisonous and stinging sea anemones. But does the anemone getting something back in return, or is the anemonefish something like a parasite to the anemone? In fact, far from a parasite, the anemonefish is actually a benefactor to the sea anemone. It was shown that anemones hosting anemonefishes grew up to three times faster than those without any clowns. First of all the anemonefish keeps the anemone clean. It removes debris accumulating on the surface of the anemone and eats the fecal materials of the anemone. The excrements of the anemonefish on the other hand are rich in ammonium and act as an important nutrient source for the zooxanthellae, the little unicellular organisms living in the sea anemones. Likewise the movements of the clowns
between the tentacles of the anemones increase the circulation of oxygen-rich water and facilitate the absorption of nutrients. It is also known, that sea anemones housing clown guests, grow longer tentacles than lonely sea anemones. Not least the anemonefishes protect the anemone from predators (of course the heroes more than the cowards) and eats many of their parasites.
What was this thing with the sexually active male and gender transformation about again? As mentioned before, the second biggest fish of a host anemone is always allowed to take part in sexual activity with the big bossy female, and not just once a year, all the year round. Spawning usually follows a lunar calendar and takes place near the time of full moon, thus anemonefishes are often called sea werewolves (“that wasn’t true!”). Three to five days before spawning, the lucky male and bossy female begin with their courtship dances. They lean against each other and shake their heads. Beside those dances a typical courtship behavior is the male “substrate biting” (“what the heck is that?”). The male bites the substrate of the nest area and in doing so prepares it, cleans it and apparently appeases the dominant female through this ritual (“you love your life, don’t fight your wife”). The actual nest lies next to the base of the anemone and consists of a hard substrate, a piece of rock, coral pavement, a shell or even debris like tin cans, coconut shells or plastic pieces (“yes for once the plastic trash is useful a bit, beside all the damage it causes otherwise”). Just before spawning, the females belly becomes bigger as the eggs inside her abdomen become hydrated. At this point the pair begins to nip on the anemone’s tentacles, causing them to retract and fully opening up the spawning site.
The female presses her abdomen then against the substrate and squeezes the eggs out. The male follows close behind and fertilizes the eggs (“I hope the description wasn’t too detailed”). This procedures takes up to two and a half hours and after that, the female swims away and the male starts its main duty: guarding the eggs. The subordinated male fans the eggs with his pectoral fins, keeps them oxygenated and removes any debris which accumulates on them. He even eats infertile eggs, or eggs that suffered fungal infections (“that’s real parental love”) and chases away any predators, which come close to its nest (“even the coward group becomes quite aggressive during this period). After 7-8 days, the eggs hatch and the small larvae swim into the water column to join the plankton. The larvae swim with the plankton stream from 8 to 16 days till they are fully developed baby anemonefishes. Now they come down to the reef again to find a new suitable sea anemone and start a new life cycle as the lowest ranking members of a anemonefish group. If there aren’t eaten by predators or evicted by bigger fishes in their group, they will finally transform into developed sexually active male or even bossy females.