Symbiotic relationships in the marine ecosystem

Several forms of associations exist among species. Animals form interspecies relationships which create a balance within the ocean ecosystem. These associations established among species are collectively called symbiosis.

In latin, symbiosis means living together. In other words, it is a close association between two different species in which at least one of them benefits.

Thus these relationships are not always mutually beneficial and are more valuable to only one party.

There are three basic forms of symbiosis: mutualism - commensalism - parasitism.

1. Mutualism

Situation where two species benefit from the relationship. Both animals rely on each other for food, protection and/or other reasons.

✔️ Example 1 : gobies and pistol shrimps

A large number of goby species live together in the same burrow with one or more species of nearly blind alpheid shrimps (aka pistol shrimps).

✅ The shrimp cleans and maintains the burrow

✅ while the goby acts as a lookout.

When "working" at the entrance of the burrow, the shrimp maintains contact with the goby with one of its antennae and the goby warns the shrimp of potential danger with a flick of its tail.

This is a very close association and they may even settle from the plankton together as juveniles.

✔️ Example 2 : anemone fish (aka clownfish) and sea anemone

Thanks to Walt Disney's movie NEMO, this is probably the most famous mutualistic association.

✅ The incredibly brave clown fish is pretty territorial and protects its anemone from predatory fish (like butterfly fish) craving for the nutrient-rich tentacles. They also keep their host clean and provide it with nutrients.

✅ In return, the anemone provides a safe and protective home to the clownfish thanks to their nematocysts. These are stinging cells located on its tentacles releasing a toxin when touched by another animal. While most fish succumb to these stings, clownfish are protected by a thick layer of mucus (mix of their own coupled with the anemone's mucus). They can therefore live within the stinging tentacles which literally protect them from numerous predators.

✔️ Example 3 : corals and zooxanthellae

Zooxanthellae are photosynthetic single-celled algae that live within the tissue of most corals and give them their colour.

✅ The coral offers the zooxanthellae a protected environment and nutrients (carbon dioxide) to carry out photosynthesis.

✅ The algae produce nutrients through photosynthesis (process that converts carbon dioxide and metabolic wastes into sugars and oxygen).

2. Commensalism

Type of relationship where only one species benefits while the other is unaffected. This happens when one species lives with, on or in another species known as the host.

✔️ Example 1 : sea turtle and remora

✅ The latter benefits from a means of transportation and gets food when the turtle feeds as it swims around to catch anything that falls off the turtle's mouth.

➖ The turtle doesn't seem to suffer from the remora getting a free ride.

✔️ Example 2 : barnacles and whales

Barnacles are small crustaceans that attach themselves to the whales (or sea turtles).

✅ By attaching itself on the latter, the barnacle gets to move around plankton-rich waters where it can feed on micro-organisms.

➖ According to scientists, the barnacle doesn't seem to hurt the skin of the whale.

3. Parasitism

This is when one species benefits while the other is harmed. The parasite lives with, on or in the host at the latter's expense. It does not immediately die from this but may sicken and die over time.

Most parasites are internal and thus unseen but a few are external.

Example 1 : isopods and anemone fish

Isopods are parasites that may invade hosts through their gills and attach themselves to the inside of the mouth. Award-winning macro photos often show a clown fish with an isopod inside its mouth.

❌ The isopod drinks blood from the fish's tongue, draining it so much that the organ dies and falls off.

Exemple 2 : barnacles and swimming crabs

While barnacles are harmless to whales, this is not the case with swimming crabs.

❌ They root themselves within the crab's reproductive system. It doesn't die from this but this impairs its reproductive capabilities.

Sylvia Earle : "We need to respect the oceans and take care of them as if our lives depend on it. Because they do."

Symbiotic relationships are studied by scientists a.o. in order to assess the health of an ecosystem. E.g. when temperatures increase, the coral expels the algae living within it, then turns white and dies. This underlines the importance of not only studying the symbiotic relationship itself but also the negative impacts that humans can have on these interactions.

Want to know more and observe all this happening live in front of your eyes? Join us, dive and enjoy our biology presentations held onboard!

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