Monday, March 21, 2011

Nemo Really Does The Finding

[6] Introduction

Sea anemones and clownfish engage in a mutualistic relationship that offers protection and increase in food availability to both.
Sea anemones have tentacles that usually sting and repel other fish, excluding clownfish, which are shielded by protective mucus that covers their bodies. This allows the close proximity of clownfish and sea anemones so that the sea anemones provide protection for the clownfish by stinging and deterring clownfish predators that come near and provide food by allowing the clownfish to eat the leftovers of what the anemone has consumed [2]. The clownfish provide better water circulation, rid the anemone of parasites, drop scraps of food for the anemone [4], and defend the anemone from butterfly fish that eat their polyps [6].

All 27 species of clownfish engage in this mutualism but only 10 out of 1,000 sea anemone species allow clownfish to live with them [2]. Of all the clownfish, Amphiprion clarkia (which is not Nemo) is the only species that can interact with all possible anemones[3]. They live in the warmer waters of the Pacific and Indian Oceans around Japan, Indonesia, northwest Australia, and along the southeastern coast of Asia [3]. A. clarkia can either live alone, in pairs, or in colonies within a single sea anemone, with the biggest in the colony being the dominant female, and the second largest being a male [6].

Description of the Relationship

The relationship between sea anemones and clownfish is a mutualistic relationship because both benefit from the relationship, providing each other with both food and reciprocal protection from their respective predators. Sea anemones can also form relationships with hermit crabs, but crabs carry anemones on their shells for their own protection and do not provide protection or food in return like clownfish do [6].

E. quadricolor, H. crispa , H. magnifica, M. doreensis, S. gigantea, and S. haddoni are among the sea anemone species that interact with clownfish [7], with Amphiprion clarkia being the most flexible and well-adapted clownfish to the anemones [3]. The relationship between anemones and clownfish has developed to be absolutely crucial to the survival of the clownfish since they are quickly eaten by predators when they are apart from their host anemones [1]. The reproductive fitness of the clownfish depends heavily on the protective quality of the anemo
nes’ stinging nematocysts, so if the ancestors of clownfish were free-living, it apparently became more beneficial for them to live within the confines of the protection of the sea anemones than to live freely on their own.

The relationship between the two is established by a juvenile clownfish seeking out the same species of anemone that their parents occupied, possibly through chemical signals and cues that were imprinted upon them as embryos [3]. The clownfish establish contact with an anemone by making quick contacts with anemone’s stinging tentacles and its belly. The tentacles actually sting the clownfish at first, but after several hours they become immune to the stings and venture into the anemone [3]. Once contact is established, the clownfish reside in the anemone and will even move with the anemone if the anemone b
ecomes distressed enough to relocate. The clownfish often stay within a radius of 2 meters of the anemone, since their chances of survival dramatically decrease if they venture away from the anemone [8].

Cost and Benefit

For the sea anemone, there seem to be no cost, since it gains increase in food availability and protection. The clownfish keep away butterfly fish that would otherwise consume their polyps; in fact, when clownfish were taken away from sea anemones in an experiment to see how long it would take the fish to repopulate them, the sea anemones were gone within 24 hours [9]. The clownfish also fan water around the anemone to increase circulation and the opportunity for the anemone to come into contact with a food source. Sometime, the clownfish will even seek out food to feed to the anemone. Additionally, they clean debris from the anemones by ridding the anemone of parasites and eating leftover food such as copepods, algae, isopods and zooplankton [2].

In a study carried out by S.J. Holbrook and R.J. Schmitt in French Polynesia over a three-year period, researchers determined that the presence of clownfish can have a significant impact on the physical condition of the anemone. Among their findings, they determined that anemones with fish grew 3 times faster than those that didn’t, they underwent asexual reproduction more often, and they had a lower mortality rate [5]. So there are direct correlations between the presence of the clownfish and the health and reproductive fitness of a sea anemone.

The clownfish also benefit extensively from their relationship with the sea anemones. They are provided with a food source when they are cleaning the anemone, and they are given protection from predators that are typically not immune to the nematocysts of the anemone. But, there is a slight cost to the clownfish; sometimes they will take their protective duties so seriously that they will engage in risky behavior in order to fend off predators of the anemone [2]. The clownfish will even try to ward off divers by trying to bite them, when a human is clearly much bigger and more dangerous to the fish. So by having a relationship where the fish risks it life for the anemone, a slight cost arises for the fish, but it is drastically outweighed by the protective service and food supply of the sea anemone.



  1. it seems that sea anemones need the clownfish to survive, but you stated that only 10 out of 1000 sea anemones allow clownfish to live within them. Do you know why this is?

  2. It is similar to how we read in ch 2 of "The Art of Being a Parasite" that Polypodium hydriforme is the only species in it's phylum of 10,000 other species that is parasitic...not all sea anemones require clownfish mutualism because they all have different physiological characteristic that could make a mutualistic, parasitic, or commenal relationship either more or less beneficial to it.

  3. Is there a benefit to the anemone? I read that the benefit of the clownfish's presence is an increase in growth rate. However, you also stated that the polyps undergo asexual reproduction. Is this common or not (I mean can they only reproduce asexually)? If it is a "choice" between sexual and asexual reproduction then aren't the clownfish costing the anemone genetic variability? Without genetic variability, according to the Red Queen Hypothesis, aren't the anemones more susceptible to falling into an evolutionary lag with a competing adversary (none come to at the moment)?

  4. The polyps always reproduce asexually, it is not a choice. The anemones with clownfish grow faster because they have an increased supply of food from the fish, and they are generally more healthy because the fish rids them of ectoparasites.