Animals depend on one other to survive. They work together in many different ways. They can also work against one other. All these different relationships are known as symbiosis.

There are four main types of symbiosis: mutualism, commensalism, parasitism, and competition. To learn about these relationships, let's take a dive in the ocean.

Mutualism

Imagine you are diving deep in the Pacific Ocean. Here, you'll probably find a colorful clownfish in the middle of a group of sea anemones. You just found your first case of mutualism.

Mutualism is when two species, or kinds of animals, help each other out. Sea anemones live attached to coral reefs. They have stinging tentacles that can stun fish. Anemones drag stunned fish into their mouths and eat them.

There is one type of fish that is safe, though. Clownfish have a special mucus on their bodies. It stops tentacles from stinging them. Clownfish are able to swim comfortably between the anemones.

Other fish see the brightly colored clownfish. They come down looking for a meal. The bigger fish are then caught and eaten by the anemones. This way, the anemones get to eat. At the same time, they keep the clownfish safe.

Commensalism

Commensalism happens when one species lives with, on or in another species. This other species is called the host. The host is not helped or hurt by the relationship.

One example is barnacles and whales. Barnacles are tiny sea creatures that live in shells. They attach themselves to the skin of whales, which do not seem bothered by it. The huge whales carry the tiny barnacles to waters where there's plenty of food. There, both animals eat tiny organisms called plankton.

Parasitism

Some relationships aren't so nice. Parasitism happens when one species, the parasite, lives with or inside a host species. Parasites hurt the host, but they do not kill it immediately.

Some common parasites in the ocean are leeches and barnacles. Although barnacles have a different relationship with whales, they are parasites for swimming crabs. A barnacle may root itself inside a crab. It lives there, but it does not kill the crab.

Competition

Our last example of symbiosis is competition. This is when animals compete over food or space. Competition can happen between members of the same species. This is called intraspecific competition. It also happens between different species. This is called interspecific competition.

Coral and sponges have interspecific competition. Coral are sea creatures with tentacles. They use calcium to create a hard coral reef, where many animals live. Sponges are sea creatures that also live on coral reefs. If they eat too much, the coral do not have enough food to survive. If too many coral die, the reef ends up disappearing. This is bad for the sponges too. They begin to die off unless the reef is balanced again.

Symbiosis helps us understand how healthy the ocean is. Right now, the oceans are heating up because of global warming. Scientists say people burn too many fossil fuels. Fossil fuels include natural gas, oil, and coal. Burning them creates greenhouse gases, which stay in the air around Earth. They trap heat and make the world hotter. Hotter water causes coral to lose the algae inside them. Algae is a seaweed-like plant. Without algae, the coral turn white and die.

The symbiosis between coral and algae tells us if the ocean is healthy. It also shows how humans are hurting the environment.