How the Clownfish and Sea Anemone Help Each Other

Biological Strategy

Clownfish

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Image: Samuel Chow / CC BY - Creative Commons Attribution alone

Cycle Nutrients

In ecosystems, there is no such thing as waste. Instead, one organism’s waste can be considered as another organism’s resource, and the cycling of nutrients may be the most important form of recycling in living systems. But sometimes those nutrients are transformed by one organism into a form that isn’t readily used by other organisms. For example, lignin is a complex organic molecule found in the cell walls of plants. In a forest, it’s one of the hardest molecules to break down in woody vegetation. Therefore, ecosystems include organisms that are particularly well-adapted to break down different types of nutrients. In the case of lignin, some fungi and bacteria release lignin-modifying enzymes that can break down the lignin to form carbohydrates and other life-supporting chemicals.

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Cooperate/Compete Between Different Species

From parasitism to mutualisms, there are endless interactions between organisms in nature. Interactions between species that lead to a negative outcome for one species are known as competition. Cooperation occurs when organisms work together for the benefit of each organism or species. While competition often occurs over resources or mates, the more biologists have begun to look for examples of cooperation in nature, the more they have found. For example, around 90% of plants have a beneficial partnership with fungi. Fungi provide the plant with nutrients such as nitrogen and phosphorus, in exchange for sugars from the plant.

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Coordinate Systems

Nature is full of systems that work in harmony by following simple rules that lead to complex behavior, such as fish swimming in a school or migrating grasshoppers flying in swarms. Coordinated behavior is also observed in how a slime mold grows, how our own neural network functions, and how some animals vote on where to live or move.

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Coevolve

Multiple living systems sometimes have such a close relationship that they end up evolving together; this is called coevolving. Coevolution occurs when changes in one living system’s genetic makeup results in changes in the other. Coevolution can result from positive, mutually-beneficial relationships. It can also result from negative relationships, such as that between a virus and its host. The host changes to avoid the virus’ harmful effects, which in turn causes a change in the virus so it can continue to predate on the host, and on through time.

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Protect From Microbes

In living systems, microbes play important roles, such as breaking down organic matter and maintaining personal and system health. But they also pose threats. Bacteria can be pathogens that cause diseases. Some bacteria create colonies called biofilms that can coat surfaces, reducing their effectiveness–for example, inhibiting a leaf’s ability to photosynthesize. Living systems must have strategies for protecting from microbes that cause disease or become so numerous that they create an imbalance in the system. At the same time, living systems must continue living in harmony with other microbes. Some living systems kill microbes. Others repel without killing to reduce the chances that microbes will adapt to the lethal strategy and become resistant to it. For example, some pea seedlings exude a chemical that inhibits biofilm buildup.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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One provides shelter, the other provides fertilizer, and both are better off for it.

Introduction

Of the more than 1,000 anemone species that live in the ocean, only 10 species coexist with the 26 species of tropical clownfish. Within these species, only select pairs of anemone and clownfish are compatible. Together, they are obligatory symbionts, which means that each species is highly dependent on the other for survival. Symbiosis between the two species is achieved in a variety of ways including a mutual protection from predators, an exchange of nutrients, and the clownfish’s tolerance of anemone nematocysts.

The Strategy

In order to live among the anemone, clownfish protect themselves from nematocyst strikes. Nematocysts are harpoon-like stingers on the anemone’s tentacles used to capture prey and ward off predators. While other fish approach the anemone as a potential food source, the clownfish doesn’t even try to eat the nutrient-rich tentacles. This avoids triggering an attack from the anemone.

The sea anemone and the clownfish have a mutually beneficial relationship.

On the off chance the clownfish is struck, it is protected by a thick mucus layer. The clownfish is born with a mucus layer that is already thicker than average, but as it grows it can become three to four times thicker than on other fish. It may even incorporate some mucus from the anemone itself.

In return for a safe and protective home, the clownfish benefits the anemone in several important ways. These include cleaning the anemone, providing nutrients in the form of waste, and scaring away predatory fish such as the butterflyfish.

The Potential

The clownfish mucus layer could inspire coatings that protect humans underwater from punctures, scrapes, and stings. But perhaps more importantly, studying the relationships between organisms that rely on one another reminds us that a single strategy isn’t always the most effective. Like nature, much of science relies on incremental discoveries that together lead to innovation. Each scientist shares information and data that can be used by others to advance their own research and add to the overall body of human knowledge.

This summary was contributed by Allie Miller.

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Last Updated June 18, 2020

References

“The clownfish Amphiprion clarkii is able to live unharmed amongst the tentacles of the sea anemone Stichodactyla haddoni. The latter has a powerful stinging response and would be capable of capturing any non-symbiotic fish that entered the tentacles. The presence of clownfish affects the anemone’s behaviour but does not impair its stinging ability, suggesting that a general inhibitory effect mediated by the anemone’s nervous system is not involved. A. clarkii achieves protection from stinging by means of its external mucus layer. This layer appears to be three to four times thicker than that of related fishes that do not inhabit anemones and consists largely of glycoprotein containing neutral polysaccharide. The mucus of A. clarkii remains inert after exposure to extreme denaturing conditions, suggesting that it does not contain specific nematocyte inhibitors or excitatory substances that are masked chemically; its inert nature probably results from a lack of those stimulatory compounds that are present in the mucus of non-symbiotic fishes.” (Lubbock et al. 1980:35)

Journal article

Why are clownfishes not stung by sea anemones?

Proc. R. Soc. Lond. B 207, 35-61 (1980) | R. Lubbock, David Cecil Smith

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