Symbiotic Relationships in the Ocean

A symbiotic relationship is one where two different species interact with each other. These interactions create a balance within the ecosystem because at least one of the species is gaining from it. The other species may also gain from the relationship, be unaffected or even get harmed from the relationship. Symbiotic relationships are very common in the ocean. especially near coral reefs.  There are four different types of symbiotic relationships. They are mutualism, parasitism, commensalism and mimicry. In this post I will provide a few examples of each of these relationships that can be found between marine life.


Mutualism is a a symbiotic relationship where each of the two different species benefit from each other.

Arguably the most important example of a mutualistic relationship in the ocean is the one between coral and zooxanthellae. Zooxanthellae are photosynthetic algae that lives inside the corals tissues. The corals provide the zooxanthellae protection and in return, they produce oxygen to help the corals remove waste.

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Coral Polyp” by emaze

Another mutualism in he ocean is between spider crabs and algae. This relationship benefits both of these species because the greenish-brown algae lives on the spiders back, which helps the spider crab blend into the shallow areas of the ocean floor where they live. In return, the algae gets a good place to live.

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Japanese Spider Crab” by (OvO) under Flickr

Cleaner fish and larger fish share a mutualistic relationship. This is because the cleaner fish eats harmful parasites and other small sources of food off of the large fish. This gives the cleaner fish a meal, the larger fish is helped because it no longer has these parasites on them. Often times larger fish wait in “cleaning stations” for the cleaner fish to come and get these things off of them. Some small shrimp can also be cleaners. The picture below shows a cleaner shrimp cleaning a large fish that would normally eat the shrimp if it wasn’t for this mutualism.

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Dangerous Dining” by Chris Lewis under Vimeo

Fish and sea anemones share a mutualistic relationship. The fish uses the sea anemone for protection from predators and they live in them. In return, the fish occasionally feeds the sea anemone and the fish also protects it from organisms that might try and eat the anemone. A popular example of a fish that does this is a clown fish.

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“Clownfish and Sea Anemone” by Samuel Chow under Flickr

Although there are many more mutualistic relationships between marine animals, the last one that I will talk about is the relationship between the Boxer Crab and anemones. In this relationship, the Boxer Crab carries around two anemones that sting and it uses them for protection. The anemones are benefited because since the crab carries them around, it allows them to be mobile which increases their options for finding food.

Image result for boxer crab and sea anemone

Boxing (Pom Pom) Crab” by  liquidguru under Vimeo



Parasitism is not a mutualistic relationship because only one of the species is benefited. The parasite gains from the relationship while the other species involved is harmed.

One example of a parasitic relationship is between fish lice and small fish hosts. The fish can be killed if there are too many fish lice attached to it. The lice benefits from the fish by feeding off of their bodily fluids.

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“Sea Lice on Salmon” by 7Barrym0re under  public domain

Isopods can also cause a parasitic relationship. Some isopods will eat the fishes tongue and then live in the fishes mouth so it they can eat whatever the fish is attempting to eat.

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“Betty in Mouth” by University of Salford Press Office under Flickr


Commensalism is a relationship where one species benefits from another species. The other species  is neither harmed nor helped in this relationship. There are many examples of commensalism in the ocean.

One example of commensalism among marine life are jellyfish and small fish. The small fish will typically hide inside of the jellyfish’s stinging tentacles if the stinging does not effect them. The tentacles provide protection for the fish from larger predators. This relationship has no effect on the jellyfish.

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“Baby Fish Take Shelter in Jellyfish” by Earth Touch News Network

Another relationship is between shrimp and a featherstar. The shrimp will blend in with the featherstar and use it for protection. As you can see in the picture below, it is very difficult to find the shrimp hiding in there.

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“Shrimp in Featherstar” by prilfish under Flickr


The last kind of symbiotic relationship is mimicry. Mimicry is when one organism that is harmless evolves to look similar to another organism that is poisonous. This stops predators from eating them because they think they are the poisonous species. They can also use mimicry to appear larger than they really are.

The four-eye butterflyfish uses a large eye spot in order to appear larger to predators.

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“Chaetodon capistratus1” by Chris Huss under  public domain

Another example of mimicry is between the Sabre-tooth Blenny and Cleaner Wrasses. The Cleaner Wrasse have a mutualistic relationship with larger fish so they don’t get eaten, and the Sabre-tooth Blenny takes advantage of this relationship by evolving to look very similar to the Cleaner Wrasse. Instead of cleaning the larger fish, the Sabre-tooth Blenny will take a bite out the the large fish’s flesh and swim away.

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“Bluestreak cleaner wrasse” by Nemo’s great uncle under Flickr
“Sabre-tooth blenny” by Fish Index

On the top there is a bluestreak cleaner wrasse and on the bottom is a sabre-tooth blenny. You can see how similar they look and how fish could mistake them.

4 thoughts on “Symbiotic Relationships in the Ocean

  1. Beautiful examples and images of mutualisms here! The sabre-tooth blenny is apparently an ectoparasite, so interesting! And a very cool example of aggressive mimicry! I love the gif of the crab with anemone pom-poms!


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