To survive, animals learn how to share — or not share — the spaces where they live. Creatures interact with one other in different ways. All of 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 imagine diving deep into the ocean.
Mutualism
Imagine you are diving in the Pacific Ocean. Here, you might spot a group of clownfish swimming in a bed of sea anemones. You've just found an example of mutualism.
In mutualism, both species help each other in some way. Sea anemones are creatures that live attached to coral reefs. When another animal touches an anemone, the anemone's tentacles release poisonous chemicals. This stuns the animal, and allows the anemone to bring the animal into its mouth.
Clownfish are safe from anemones. They have special mucus on their bodies that stops the tentacles from stinging. The lucky clownfish are able to swim comfortably between the anemones. Meanwhile, when bigger fish see the brightly colored clownfish, they come and try to eat them. These unsuspecting fish get killed off by the anemones.
Clownfish help the anemones get food. The anemones help keep clownfish safe. This is why their relationship is an example of mutualism.
Commensalism
Commensalism is when one species lives with, on or in another species. This other species is called the host. The host is not helped by the relationship, but it isn't hurt either.
For example, barnacles attach themselves to the skin of a whale. Barnacles are small sea animals that live in shells. They do not seem to bother the huge whale, which carries the barnacles to plankton-rich waters. There, both species get to eat a large amount of plankton, which are tiny sea organisms.
Parasitism
Another harmful relationship is parasitism is a harmful relationship. This happens when one species, the parasite, lives with, on or in a host species. The parasite is bad for the host species. Unlike in predation, the host is not immediately killed by the parasite, though.
Some common ocean parasites 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's reproductive system. The crab does not die from this, but it has a much harder time having babies.
Competition
When organisms fight over the same space or food, they are in competition with one other. Competition between members of the same species is called intraspecific. Competition between different species is called interspecific.
One example of interspecific competition is the relationship between coral and sponges. Coral are underwater creatures with tentacles. They use calcium to create coral reefs, where many other animals live. Sponges are sea creatures that are common in coral reefs. They eat food that coral also need in order to survive. Sometimes, sponges may beat out coral for that food. If this happens, and too many coral die, the reef starts to disappear. That means sponges won't be able to live on the reef either, and they start dying off until the reef gets balanced again.
By looking at symbiosis, humans can understand how healthy an ecosystem is. For example, Earth and its oceans are heating up because of global warming. Scientists say this is because of the fossil fuels we burn, such as natural gas, oil, and coal. Burning them creates greenhouse gases, which stay in the air and trap heat. When ocean water gets hotter, it hurts the coral reefs. The higher temperature causes coral to force out algae, a kind of seaweed that lives inside them. Without their algae, the coral turn white and die.
The symbiosis between coral and algae tells us how the ocean is doing. It also helps us understand how humans are hurting the environment. In the words of National Geographic Explorer Sylvia Earle: "We need to respect the oceans and take care of them as if our lives depend on it. Because they do."
