What's That Word? Symbiosis.

There are several popular terms that science has supplied to the general vernacular. One of the most relevant to us as aquarists is “symbiosis.” We can see countless examples of symbiotic behavior in nature, and a few are options for a display in your aquarium. This being said, it's a somewhat misunderstood term. We use it as a catch all for a relationship between two species that benefit both parties equally, and this has certainly happened, but there are other kinds of symbiotic relationships.

Symbiosis is really a term that means two different species have a long-term interaction. You are having a symbiotic relationship right now with billions of bacteria in your digestive system. This is an example of mutualism, where two species benefit. You give the bacteria a safe place to live and reproduce, while they break down food for you into components your body can actually use. One of the most iconic mutualistic relationships in the ocean is the one between an anemone and a clownfish where the clown gets protection from the nem, and the anemone gets care from the clowns who will remove waste from it and sometimes will even bring it food! Some will argue that the anemone is not meaningfully benefited in this relationship, making it an example of the next category.

Another relationship that falls under the umbrella of symbiosis is “commensalism.” A good example of this relationship is the one between Banggai Cardinals and Long Spine Sea Urchins. The young Cardinals can hide among the protective spines of the urchin, but supply nothing we can discern back to it in return. Commensalism is any relationship where one species is benefited, and the other remains unaffected. Other good examples of this are remoras and sharks, Emperor Shrimp and Sea Cucumbers and sometimes Zebra Crabs and Urchins; though depending on the species of Zebra Crab, which may or may not feed on the urchin itself, this relationship might also fall into the next category.

The third category of symbiosis is called Parasitism; in this relationship, one species is benefited, but to the detriment of the other. It is the basis for the word parasite. Most enteric worms fall under this category. If your pets (or you) have ever been unlucky enough to have worms, you'll have had some experience with this. The worm can live inside another organism for long periods of time, and gets protection and food, but the host organism loses nutrients to the worm. The world is absolutely chock full of examples of parasitism: ticks, mosquitoes, even mistletoe. However, aquarium displays feature very few examples of it though on rare occasion you will see a Pearlfish in a display. Pearlfish will live inside the cavity of a sea cucumber. Some Pearlfish will also consume the Sea Cucumber from the inside, making it a parasitic relationship. Other species of Pearlfish won't harm the Cucumber, leaving to eat on their own, and the Cucumber isn't harmed (as far as we know) making it an example of commensalism. All of the other examples of parasitism in your aquarium are problems; things like ich, fish lice, flukes and anchor worms. Dealing with these is another article.

In almost all these symbiotic relationships, one species is the host organism, and one species is hosted. The Anemone hosts the clownfish, and the Urchin hosts the cardinals, etc. That being said, symbiosis can also be used to describe cooperative relationships between species, like the relationships between cleaner species and other fish. There is no real “host” relationship between a grouper and a Cleaner Goby, but both species benefit from their inter-species relationship; the grouper gets groomed, and the cleaner gets a meal. Fish will line up for their turn at a Skunk Shrimp's cleaner station, and all the species involved benefit, but there isn't really a traditional “host.”

The anemone / clownfish relationship is probably the most iconic of these interactions that you're likely to see in the home aquarium, but there are other opportunities for you to have in your display. Certain species of Carpet Anemones can also host Domino Damselfish, which makes for an amazing (and hugely underrated) display. The Shrimp Gobies and Pistol Shrimp are another example of Symbiotic behavior. The basically blind shrimp will dig and maintain a burrow for both species to live in, and the Goby will act as a sentry looking out for danger and signaling the shrimp when to take cover. A large Longspine Urchin and a school of Banggai (Kaudern's) Cardinals also makes for a stark and interesting display. There are many species of coral crab that can live in different stony corals where the crabs can clean and protect the corals in trade for the cover the corals provide. There are also many parasitic relationships between crabs and corals as well, so watch any unintended crabs with a weather eye.

Probably the most common symbiotic relationship in reef style aquariums is one we don't often even think about. The corals themselves can't use the light we (or nature) provide them, instead they host another organism called zooxanthellae which is photosynthetic and can use that light to make sugars for the corals to consume!

Obviously, we love marine aquariums of all types here at Quality Marine, but the ones that feature these relationships are always something special. Now go forth and plan yourself a little corner of Symbiosis in your main display or maybe plan another tank around the relationship you'd like to feature!