Symbiotic relationships describe the association between different species living in the same environment. Symbiosis comes in three forms: mutualism, commensalism, and parasitism. Mutualism describes a relationship that is beneficial to both the host and the symbiont. Commensalism describes a relationship in which the symbiont benefits from the association and the host is neither benefited nor harmed. In a parasitic relationship the symbiont is benefited at the expense of the host, which can sometimes prove fatal.

Clownfish illustrate mutualism perfectly. Anemones have stinging cells on their tentacles called nematocytes, which are used to catch and kill their prey and manoeuvre them into their digestive systems. The clown fish acclimatizes to these nematocytes by swimming slowly around the anemone?s tentacles altering its mucous sting. The anemone harbours the fish without harm. Anemones prey on everything from plankton to small fishes. Clownfish are the exception to this, and in return for their protection they provide defence for the anemone by eating one of its main predators, the polychaete worm.

An example of commensalism is the relationship between a whale shark and the fishes that tag along with it-?usually jacks, remoras, and cobias. Striped remoras can be seen clinging on to the sides of these massive fish, sucking the plankton and bacteria from their skin, and at the same time getting a free ride. Remoras are considered the hitchhikers of the ocean. Golden pilot jacks and cobia use a different tactic. These fish are wake-riders and instead of getting a free ride, they swim underneath or behind the whale shark in order to reduce drag and therefore save energy. Cobia are often mistaken for juvenile sharks when spotted from afar, for their body shape and the way they move from side to side is very characteristic of a shark.

All three of these commensals are freeloaders; not only do they get an easy ride, but they are able to feed on the scraps of food that whale sharks leave behind: krill, plankton, and small fishes. These clever symbionts benefit from this association, while the whale shark remains untroubled. There are also a number of parasitic relationships found here, and one of the largest groups of parasites are the copepods. The ectoparasitic copepods (working on the outside of their host) feed on teleost fishes and moray eels. These copepods have mouthparts adapted to pierce and suck through their host?s tissue. Some species are known to attach themselves onto the gills of their fish hosts and lay their eggs there. These parasites, however, must fight to keep their niche. There are other organisms that feed on these parasites, thereby creating another symbiosis to counter-act the parasitic one. These are the cleaner organisms that live in mutualism with their hosts. Sheltered in rock crevices in coral reef environments, divers can find areas where several organisms set up cleaning stations.

Usually cleaner species consist of shrimp, pipefish, and wrasse. Once you become aware of symbiotic relationships, you?ll be surprised how many you see underwater.

While working as a full time Divemaster in Hawaii, Anik Clemens also worked part-time at a Microbiology Lab affiliated with the University of Hawaii. She can be contacted at anikclemens@yahoo.com.