5 Symbiotic Relationships in the Ocean

5 Symbiotic Relationships in the Ocean

We all have to get along with our neighbors. It’s just the way things are if you want to enjoy a peaceful existence. Although it may be difficult because of cultural, habitual, or recreational differences, there is usually a way that people can find a balance if both are open to compromise. But how many people can say they are mutually benefiting from their neighbors without actually interfering with each other’s business?

There are three common types of symbiosis found in the ocean: mutualism, commensalism, and parasitism. For humans, it may be hard to imagine having any of the first two types, where one or both benefit from the relationship. Nonetheless, symbiosis is a system that has been in place on Earth among various species for millennia.

Check out a few of the most popular examples of marine life exhibiting the two different types of symbiotic relationships in the ocean:

Sea Cucumber and Shrimp

imperial shrimp on sea cucumber surface

The relationship between imperial shrimp and the sea cucumber is a good example of commensal species—one benefits while the other neither benefits nor is harmed.

The imperial shrimp first finds a sea cucumber. It will then utilize the sea cucumber for its locomotive purposes by hanging tight as they move through waters filled with the shrimp’s food source. The shrimp will only disembark to hunt (until it runs out of food) and then climb back aboard to travel to the next feeding ground.

In some cases, their relationship may turn into a mutualistic one—particularly with cleaner shrimp. The latter may clean algae and parasites from the sea cucumber as “payment” for the free ride.

Sea Anemone and Clownfish

clownfish swimming in sea anemone

The mutualism of the relationship between these two organisms is well-known due to the popularity of films such as “Finding Nemo.” The sea anemone and clownfish showcase a great example of mutualistic symbiosis, meaning both organisms benefit from having the other around.

The anemone protects the clownfish by concealing it within its poisonous arms (which the clownfish is immune to) and leaving scraps of its meals for the clownfish to consume. In return, the clownfish rids the anemone of parasites, wards away predators, and even offers nutrients by way of its excrement.

Interestingly, the boxer crab also shares a similar relationship with sea anemones—it feeds the anemone and, in exchange, makes use of its stinging tentacles as a defense mechanism or deterrent. Boxer crabs can often be seen with sea anemones attached to their claws, which they wave like “pom-poms” to ward off predators. They typically wave them horizontally as a warning to potential aggressors, but they may also do a forward “punching” movement (hence the name) against an attacker.

Hermit crabs also wear anemones on their shell for protection while the anemone thrives on leftovers that the crabs feed on.

Whale and Barnacle

barnacles on head of whale

Also exhibiting an example of a commensal relationship are the whale and the barnacle. The whale reaps no rewards from the barnacles attached to its body, but it also does not suffer any ill effects. The barnacle, on the other hand, reaps great rewards by attaching itself to a whale because of its filter-feeding nature.

Like the imperial shrimp, the barnacle stands to gain an abundant food source by attaching itself to a whale for the duration of its existence.

Decorator Crab and Sponge

decorator crab camouflages with sponges

A most striking balance is struck between the decorator crab and the sponges that it decorates itself with. The decorator crab does so as a means of defense, snipping bits of sponge to cover its shell as camouflage. The sponges continue about their lives, filter feeding as they normally would when attached to coral reefs or any other surface.

The crab also benefits from the toxins that may be inherent to the species of sponge it chooses and feeds on the algae growing around the sponge. The sponge benefits in the same way that the other “hitchhikers” on this list do—it benefits from this somewhat mutualistic relationship by being exposed to many feeding opportunities based on the crab’s movements.

While this is not exactly obligate mutualism, the decorator crab definitely survives longer and the sponges are able to feed more conveniently, thanks to their unique relationship.

Manta Ray and Remora

Manta Ray with remora sucker fish

Remoras are known collectively as “suckerfish” for their propensity to attach themselves to many different types of species, including dugongs, sharks, sea turtles, and manta rays. The remora, which is a fairly large fish, uses its host for the usual amenities: protection, transportation, and scraps from the larger predator’s meals. The remora can also exist in mutualism with its host and establish a cleaning symbiosis by ridding the host animal’s skin of bacteria and parasites.

The animal kingdom offers many examples of how species can coexist in mutualistic relationships under beneficial terms, or at least causing the least amount of annoyance to each other. Have we, as humans, lived up to this ancient standard as well as we can?


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