What is Symbiosis?

by Gabbie Baillargeon

Symbiosis occurs when two organisms live together, and usually become dependant on one another to survive.  There are three different types of symbiotic relationships:

  • Mutualism:  When both organisms are benefitted by the relationship
  • Commensalism: When one organism benefits and the other does not benefit, but is not harmed by the other.
  • Parasitism: When one organism is benefitted and the other is severely harmed.

Symbiosis can lead to amazing and innovative ideas on how to avoid predators and cope with their environment, check out these examples of symbiosis in action:

  1. Corals and Algae

Corals appear “bleached” or stark white in color when not housing a specific, single-celled algae called Zooxanthellae (zoo-an-thel-ee).  Within each coral polyp rests zooxanthellae colonies, which are responsible for giving corals their vibrant colors and providing vital nutrients.  Zooxanthellae undergoes photosynthesis, the process of using water, energy from the sun, and Carbon Dioxide to produce glucose, Oxygen, and other nutrients.  A study by the NOAA finds that, “90 percent of the organic material photosynthetically produced by the zooxanthellae is transferred to the host coral tissue.”  Corals then absorb these nutrients, undergo cellular respiration whose byproduct is Carbon Dioxide, which the algae then reuse during photosynthesis.  This crucial mutualistic relationship draws life to the reef, allowing it to flourish with color and vibrancy.  However, when zooxanthellae are not present in corals, reefs appear barren and devoid of life, which stresses how important their relationship is to the survival of the reef.

  1.  Sharks and Remoras   remora

Why would a small fish purposely buddy up with a shark?  It does seem like these little remoras would try to avoid being anywhere near a shark’s jaws, but instead, they have developed a mutualistic relationship with these fearsome predators.  Remoras take on the role of that “clingy” girl/boyfriend who will never leave your side. Remoras have a flat body and are a equipped with a suction cup mouth on their underside, which enables them to hang onto the shark as it traverses the ocean in search of food.  Remoras happily eat any unwanted parasites, algae or other particles – acting as a personal shark cleaner.  In return, when sharks successfully catch their prey, the remora detaches and sneakily snacks on the left overs.  Since both the shark and remora benefit from this relationship the shark tolerates the remora clinging to his side.

  1. Whales and Barnacleswhale barn

Large colonies of barnacles are often seen on various whale body parts, including the: fluke, face, and fins.  The barnacles are also filter feeders, so they greatly benefit from tagging along, because whales are constantly on the move looking for a fresh supply of microscopic plankton found in nutrient rich waters.  The barnacles enjoy the ride while absorbing nutrients from the water; however, there is no scientific evidence that whales also benefit from the barnacles.  Though it may weigh the whale down, they do not seem to experience any discomfort; therefore, they exhibit commensalism with the barnacles.

  1.  Kelp and Sea Otters

Think of the great kelp forests off the beautiful California coastline, with the deep green, leafy stalks gently swaying with marine mammals frolicing through the underwater wonderland. Naturally, sea otters utilize kelp forests as anchors by wrapping their bodies in kelp floating on the surface; allowing them to take a much needed mid-day nap.  In order to return the favor, sea otters feed on sea urchins who eat away at the roots of kelp – eventually killing them. Sea otters keep the urchin population in check and the kelp forests healthy, therefore this is a mutualistic relationship.

  1.  Classic Clownfish

Clownfish are one of the only known marine animals who are completely immune to the sting of anemones.  Made famous by the movie Finding Nemo, it is true that clown fish use anemones as homes.  They have the best security system in the marine world because anyone who tries to break in will instantly be stung, paralyzed, and definitely deterred from eating the residents.  The sea anemone is a happy landlord since clownfish keep the anemone clean by eating any dead tentacles; in addition, they lure fish towards the anemone providing a tasty treat. Just another example of mutualism.

  1.  Crabs and Anemones

crab anemClown fish aren’t the only ones who have a symbiotic relationship with anemones, Hermit and Rock crabs are also known to use anemones to their advantage.  The crabs will heft small anemones and attach them to their shell, and sometimes will even double fist anemones!  The main purpose of attaching the anemones to themselves is to deter predators from picking them up as an afternoon snack.  A sting from one of their toxic tentacles can be deadly.  The anemone also benefits from being crab luggage because they constantly catch small prey in their tentacles as the crab moves through the intertidal zone.  Yet another amazing example of mutualism!


  1.  Humans and the ocean

This is (mostly) a form of parasitism, as we enjoy the riches of the ocean without taking responsibility for our actions.  Ocean based tourism generates billions of dollars each year, and yet, we still do not take action to give back to the ocean.  Much of the world’s food is derived from the ocean, but we continue to recklessly drain the ocean, ignorant of the fact that there is not always an endless supply of fish, oil, and Oxygen for both humans and the marine ecosystem.