A Little Help from a Friend: 5 Symbiotic Marine Animal Relationships


One of the most basic lessons of life is that sometimes cooperation is better than conflict. This same principle applies under the sea and is evidenced by ‘symbiotic relationships’ that have developed among various organisms in marine ecosystems. Through the process of evolution some underwater inhabitants have figured out that they can increase their chances of survival in a hazardous fish-eat-fish world if they collaborate with others.

Symbiosis is a scientific concept that describes a close, long-term interaction between two different species where some form of benefit is gained by at least one of the partners. Symbiotic relationships occur in both marine and land animals. There are three main types of such relationships:

  1. Mutualism—describes a relationship between both partners benefit from the interaction.
  2. Commensalism—a relationship in which one partner benefits while the other is unaffected.
  3. Parasitism—a negative relationship where one partner benefits at the expense of the other.

Countless symbiotic relationships exist within marine ecosystems. Here is a list of some of those most commonly witnessed by scuba divers.

Clownfish and Anemones

Anemone_Fish_1.jpgThis is a friendship for the ages. Photo Credit: NOAA

The relationship between clownfish and sea anemone is a perfect example of mutualism, where both organisms benefit from teaming up together. Clownfish make their homes among the poisonous tendrils of the sea anemone, where they are provided shelter, protection and a place to hide from potential predators. Clownfish have developed a biological immunity to the anemone’s sting and are therefore safe in the anemone’s embrace. In return, the anemone benefits by consuming the waste of the clownfish and the scraps of food that naturally fall by the wayside as the clownfish eats. Anemone also remain vibrant from the constant aeration generated by the movement of the clownfish.

Barnacles and Whales

barnacle_whale_1.jpg Barnacles on a gray whale in Hare Eye Lagoon, Mexico. Photo Credit: Ken-Ichi Ueda

Barnacles have worked out a good deal with whales, mainly humpbacks, reaping great rewards from attaching themselves to the belly or backs of the whales. Barnacles are filter-feeders, relying on plankton that they filter through feather-like appendages that extend through holes in their shells. By hitching a ride on a whale’s body, they are carried like royalty from meal to meal as the whale swims through plankton-rich waters. An added benefit is protection from predators, as only the most courageous of predators is likely to attack a whale. For the most part, the whale remains unaffected—they can support the weight of thousands of barnacles at a time. Barnacles and whales are an example of a symbiotic relationship of commensalism.

Pistol Shrimp and Gobies

Shrimp_Goby.jpg A seeing-eye fish Photo Credit: Klaus Stiefel

Although the tiny pistol shrimp is basically blind, it has enlisted the help of the bottom-dwelling goby to act as its eyes and ears. The pistol shrimp spends its days digging small burrows in the sandy seafloor searching for food. By doing so, the pistol shrimp creates holes that are just the perfect size to provide a resting place and protective shelter for a goby. The pistol shrimp allows the goby access to the holes it digs—rent-free—as long as the goby completes one job in return: serving as watchman. When a predatory fish approaches the goby flicks its tail several times, alerting the shrimp to the coming danger. Both the goby and shrimp retreat deep into the burrow to wait out the attack.

Decorator Crabs and Sea Sponges/Anemones

Sponge_Crab_(Dromia_sp.)_(6082716840)resized-Wikimedia-Commons.jpgA decorator crab shows its style in the latest 2017 fashion. Photo Credit: Bernard Dupont/Wikimedia Commons

Decorator crabs use the time-tested art of camouflage to help them survive, attaching materials from their environment to their shells to help hide from prey. The ingenious thing is that they don’t just use non-living materials but living organisms including sea sponges and anemones as well. The decorator crab snips off pieces of sponge and anemone to add to its shell, gaining a piece of camouflage (in the case of a sea sponge) or a handy weapon (in the case of a poisonous anemone). The sea sponge and anemone both continue to live on the back of the decorator crab and, like a barnacle, gain the benefit of being transported to different feeding areas.

Sharks and Pilot Fish

Shark_Pilot_1.pngAn oceanic whitetip shark and a group of pilot fish swimming at the Elphinstone Reef in the Red Sea, Egypt. Photo Credit: Oldak Quill

The survival strategy of the pilot fish involves making the most powerful of friends. The striped fish can often be seen swimming below a shark as it cruises the sea in search of prey. The pilot fish performs the important role of cleaning the shark’s skin of parasites and the shark acts as a bodyguard in return. The ocean’s apex predator shows phenomenal restraint by not eating the pilot fish because it is aware of the benefits of being squeaky clean.

Ryan Patrick Jones