The Environmental Science Graduate Students at Watlings Castle, San Salvador, Bahamas.(TME 98)
Symbiosis is “a close, prolonged association between two or more different organisms of different species”. A symbiotic relationship is always inter-specific, meaning that it occurs between two different species. Intra-specific, or relationships within a single species, are rarely considered symbiotic. Organisms benefit by taking part in symbiosis. The symbiotic process can help reduce competition for food and territory, helping species find their environmental niche.
Symbiosis can be broken into three main categories; commensalism, mutualism, and parasitism. The first type of symbiosis is commensalism. Commensalism is “a symbiotic relationship between two organisms of different species in which one derives some benefit while the other is unaffected”. A good example of a relationship that demonstrates commensalism is between the Imperial Shrimp (Periclimenes imperator) and large sea cucumbers. The Imperial Shrimp will ride on the sea cucumbers, receiving transportation. The sea cucumber helps serves as a transporter to food sources. The imperial shrimp is able to ride on the sea cucumber, getting exposed to larger areas with more potential food sources while using less energy.
Another example of a relationship involving commensalisms is between isopods and fish. Although Isopods are usually parasitic, there are some species that attach themselves to a fish without damaging tissue. Isopods are external marine parasites which are large enough that they can often be seen by the naked eye. They use complex sucker-like organs to firmly attachment themselves to their host. The Isopods scavenge floating food particles rather than feeding on their host, as they would in a parasitic relationship.
The Goby and sea-urchins also exhibit commensalism. There are certain species of Goby, like Astropyga radiate, that live amongst the spines of toxic sea-urchins. They gain protection from their host while their host is neither advantaged nor disadvantaged by the relationship.
Another type of symbiosis is mutualism. Mutualism is an association between organisms of two different species in which each member benefits. This relationship exists between Hermatypic (reef-building) corals and zooxanthellae or coral polyps. The zooxanthellae live inside the Hermatypic coral’s tissue. The zooxanthellae consume the waste products of the coral and turn the waste into substances usable by the coral for growth and maintenance. It is certain death for the coral if there is an absence of the zooxanthellae for too long.
Another example of mutualism involves the Boxer crab (Lybia tesselata) and small anemones. The Boxer crab carries a pair of anemones in its claws. When predators approach the Boxer crab it waves the anemones, which present their stinging tentacles. The Boxer crab gets protection and the anemones get the partials of food that are dropped by the crab. Clown fish and Anemones also exhibit mutualism. The clown fish receives protection from the anemones while the anemones receive food drawn by the clownfish.
The third type of symbiosis is parasitism. Parasitism is a symbiotic relationship in which one species, the parasite, benefits at the expense of the other, the host. There are two types of parasitism, ectoparasitism and endoparasitism. Ectoparasitism is where the parasite is external and endoparasites live inside the body of the host, such as viruses, bacteria, flatworms, roundworms and leeches.
An example of an ecotoparasitism relationship is the Fish Doctor and fish. The Fish Doctor, a type of isopod crustacean, will attach itself under the fins, scales, or gills of a fish. It then sucks the blood of the host fish until it dies.
An example of an endoparasitism relationship is the pearl fish and sea cucumbers. The pearl fish is a type of mesoparasite. It detects chemicals given off by the sea cucumber and enters the sea cucumber when it participates in gas exchange and breaths in water. The sea cucumber attempts to eject the pearl fish by expelling most of their digestive tract out through their anus. This can be detrimental for the sea cucumber.
Organisms use symbiosis in many different ways to accomplish a variety of life activities. These activities include defense, cleaning, transportation, food, housing, and camouflage.
Symbiosis is commonly used as a method of defense. The symbionts select hosts with better defense mechanisms then they have. An example of this behavior exists between the Carrier Crab and Urchins. The Carrier Crab is highly creative in locating defenses. This species will carry urchins on their back for protection as it crosses the sea floor. The urchins prefer a solitary existence but are not harmed by this activity.
Symbiosis is commonly used for the purpose of cleaning. With cleaning symbiosis the symbionts don’t live in the tissues their hosts’. There is a common practice of “cleaning stations”. This is where large fish will go to the places where symbionts, the cleaner shrimp and fish, live. The cleaners pick off parasites, algae, and detritus from the larger fish, obtaining a meal from the cleaning process. This process helps maintain the health of many marine populations. There are some types of fish which even change color to indicate that they need to take place in the cleaning process, making external parasites stand out more against their skin. A perfect example of cleaning behavior is the Cleaner Shrimp and the Grouper.
Transportation is another way organisms use symbiosis. When one animal uses another for transportation, the symbiotic relationship is called phoresis. An example of this type of relationship exists between the Swimmer crab and Actinopyga. This is a commensally associated relationship between the urchin Actinopyga and the Swimmer Crab. The Swimmer Crab benefits, receiving transportation and protection from the Actinopyga.
Symbiosis is also used as a way for the symbionts to obtain food. Several different kinds of shrimp, crabs and copepods live on coral and other cnidarians surfaces creating commensally associated relationships. The shrimp/crab/copepods benefit by consuming the mucus coating, dead skin or any adhering organic particles off the coral. This activity does not harm the crustacean hosts. This activity may even result in the shrimp/crab/copepods eating off an occasional parasite, protecting the crustacean.
Organisms use symbiosis as a way of creating housing. Endoecism refers to animals that live in the shelters created by their host. An example of this type of relationship exists between the Arrow Goby and crabs. The Arrow Goby can be found in the burrows of several invertebrates. They prefer crab holes, where they live and find food. They will feed on the wastes of the host, providing the role of housekeeper. At times the food they find is too large for them to eat so they give it to the crab, providing their host with meals. This relationship also exists between the Goby and blind shrimp. The goby, unable to dig burrows, uses the shrimp as a home, the shrimp, unable to see potential predators, uses the goby as a form of protection. When a Blind Shrimp predator approaches the goby fish touches the shrimp with its tail to warn it, then both the shrimp and goby fish retract into the burrow.
Camouflage is another way organisms use symbiosis. The Pencil fish or seahorse and grass beds exhibit this relationship. The Pencil fish normally resides in the buoyant grass beds, using them to hide. The Anemone Hermit crab (Dardanusm pedunculatus) and small sea anemones also use symbiosis to create camouflage. The Hermit crab will attach several anemones to its shell, providing both camouflage and deterrent to predators. The benefit to the anemone is that it is exposed to more food with the crab as its mobile home then it would have encountered if it were stationary.
A healthy reef supports many kinds of symbiotic relationships. However, when the reef is stressed by abuse, nature or human, the relationships can fail. The break down of these relationships will most likely result in the death of the reef.
Symbiotic relationships are very common in the ocean, particularly on the coral reefs. While these relationships do have a negative affect on some species they are usually helpful. These symbiotic relationships are crucial to the success of a coral reef environment, allowing organisms to fit into a niche. If species didn’t work together then countless species in the reef system would be out competed and destroyed.
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Gillis, William T.; Byrne, Roger; and Harrison, Wyman. 1975 “Bibliography of the natural history of the Bahama Islands” The Smithsonian Institution. [found on http://www.botany.hawaii.edu/faculty/duffy/arb/191/v191.pdf]
Hall, David. “Symbiosis.” [found on http://www.seaphotos.com/symbiosis.html]
Hatcher, B.G. “Coral reef ecosystems: how much greater is the whole than the sum of the parts?” Coral Reefs (1997) 16.
MarineBio.org. “Symbionts, Parasites, Hosts and Cooperation” [found on http://marinebio.org/Oceans/SymbiontsParasites.asp]
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Strickland, Mark. 2005 “Invertebrates” [found on http://www.oceanic-impressions.com/invertebrates.htm]
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