Over several thousand years, coral reef animals have formed some strange relationships. There are three types of relationships that are generally called symbiotic relationships. Coral reefs have many excellent examples of such relationships. Specific names and relationships are listed below.

Parasitism:
In this relationship one animal benefits from the relationship but the other suffers from the relationship.

Commensalism:
In this relationship one animal clearly benefits from the relationship but the other does not. However, unlike the parasitism relationship, the animal that does not benefit does not suffer or get damaged from the relationship.

Mutualism:
In this relationship both animals benefit from the relationship. Many people call mutualism a symbiotic relationship.

To learn more about some of these strange relationships please click on one of the links below.

1. Dentists and Cleaners
2. Tricky Cleaners
3. Strange Home Security
4. Hide and Seek
5. Goby, the Guard Dog
6. Hitchhikers

The coral reef has tons of tiny colorful fish called wrasse. They are more commonly called cleaner fish. Bigger fish love to get their teeth, gills, skin, and mouths cleaned by the tiny wrasse cleaner fish! The wrasse picks out the parasites from the bigger fish and this becomes their meal. Did you know that the bigger fish will not eat the tiny wrasse even when it swims inside its mouth? It is incredible! This is a great example of mutualism because the bigger fish gets a clean and the little fish gets a meal. They help each other out and don't hurt each other. Both animals benefit from the partnership. In some cases, the wrasse even cleans wounds of dead skin and debris. It is said that the wounds heal faster this way than they would have on their own.

Wrasses are not the only type of cleaner fish. Butterfly fish, gobies, banded coral shrimp, and gray angelfish also form partnerships with bigger fish the same way the wrasses do.

A School of Wrasse Photo © Steve Turek, ICRIN

A school of masked butterfly fish Photo © Lyubomir Klissurov, ICRIN

A Gray Angelfish swimming in front of a yellow branching tube sponge Photo © Chuck Savall, ICRIN

Scientists have recently discovered that these tiny cleaner fish happen to remove some pieces of healthy scales and bits of fin along with parasites and dead flesh during the cleaning. If you think about it, this cleaning is not fully helpful to the bigger fish. But the scientists think that the bigger fish enjoy the cleaning. Have you ever had an itch and enjoyed the pleasure of having that itch scratched? Scientists think that the bigger fish get the same kind of pleasure when the cleaner fish clean them, so they are willing to put up with the cleaning. Cleaner fish are very important to the reef ecology. If they leave the reef, along with them many other types of fish life will leave as well.

There is a type of fish called the saber-toothed blenny that looks like a cleaner fish. They are really tricky and they know very well that they can make the big fish think they are the cleaner type. They swim near the big fish and when the big fish waits, still hoping to enjoy a pleasurable clean, the saber-tooth blenny swims close and quickly takes a quick bite of the big fish, then darts away quickly. This is a good example of a parasitic relationship.

Portrait of a yellow-green blenny hiding in the groove of a green brain coral; Photo © Chuck Savall

There is a very strange relationship between a sea anemone and the hermit crab. The hermit crab picks up tiny sea anemones and puts them on its back. The stinging tentacles of the sea anemone protect the crab from other vicious animals. They also provide camouflage. During the ride on the back of the hermit crab, the anemone gets scraps of food that float up when the crab eats. When the crab grows too big for its old shell, it moves into a new shell; however, it takes its anemone friend with it! It is surprising to the scientists how carefully the crab transfers the anemone from its old to new shell.

Hermit crab with anemones on its shell Photo © Lyubomir Klissurov

Many small fish use sponges or sea urchins as hideouts when danger approaches. This is an example of mutualism as both animals benefit from the relationship. Remoras, a special kind of fish, also have the same type of relationship with turtles, sharks, and manta rays. The remoras have suction cups that they use to attach to the bottom side of these reef animals. They can stay attached even when these animals swim fast. The remora attaches to these animals because whenever the animal it rides on stops for a feed, the remora detaches itself, feeds on scraps, and attaches back to the animal for yet another ride. The remoras also eat the parasites that live on the animals they ride on. When the remoras remove these parasites, the reef animal is relieved from the discomfort of the parasites. Although the remora seems to get more out of this relationship than the animal that it pairs with, this is a good example of mutualism as both animals get something from each other out of the relationship.

Note: All photos used on this page are from ICRIN. Photos from ICRIN are available free for non-commercial use with credit to the photographer.