- 1 Soft Corals
- 1.1 Structure and Biology
- 1.2 Distribution and Habitats
- 1.3 Food Source
- 1.4 Behavior
- 1.5 Reproduction
- 1.6 Human Influence
- 1.7 Class Photos from the US/British Virgin Islands in the Caribbean
- 1.8 References
Soft coral is also known as Alcyonacea and ahermatypic coral, which is a type of coral that does not secrete calcium carbonate skeleton or form reefs. They are normally colorful and look like underwater plants that swing with the waves in the ocean. They are colonial, and often times little polyps combine together to form a large organism. 
Structure and Biology
Soft corals have a flexible skeleton which is made of a protein called gorgin and calcium carbonate.  They have sclerites, which is a spiky skeleton element that supports their vertical structure as well as gives them texture. They also have gorgonin in the inner core of their colony, which is a type of fibrous protein that enables the flexibility of soft corals and their swinging movement along with the ocean waves. Their polyps are anatomically separated from each other, as each polyp is a separate living organism. 
Soft coral polyps have eight tentacles. Each polyp is shaped like a cup with a ring of tentacles around a central opening called a pharynx that functions as the mouth and anus of the organism. On the tips of coral tentacles, there are stinging cells called nematocysts, which are used to defend themselves and to capture prey like zooplankton. Most corals extend their polyps at night since that is when zooplankton is the most abundant. 
Types of Soft Coral
There are many types of soft corals, but all of them belong to the order Alcyonacea under the subclass Octocorallia. Octocorallia refers to corals with eight-branched tentacles in their polyp structure. Alcyonacea is further divided into families and suborders. 
|Astrospiculariidae||Consists of one genus from the Pacific Ocean. Bushy looking, low growing, and normally are green.|
|Clavulariidae||Commonly known as Palm Tree Polyps, and Clove Polyps. Consists of a few diverse corals, contained in four subfamilies. Polyps can have long tall stalks with either feathery or stark tentacles.|
|Nephtheidae||Most colorful and 'fluffy' of the soft corals. Can be bushy or tree-like with beautiful colors: red, pink, yellow, and purple. Examples are Carnation Coral and Tree Coral.|
|Siphonogorgiidae||Commonly known as China Corals. Form large tall colonies with thin and brittle branches. Typically are red with contrasting white of yellow polyps. Rarely available.|
|Xeniidae||Both pulsing and non-pulsing varieties. Pulsing means corals' polyps will pump water into the colony, which would create a rhythmic pulsing motion. Colors can be white, brown, or blue. Many have long feather-like tentacles.|
Distribution and Habitats
Soft Corals can be found in waters world wide but primarily exist in tropical or subtropical climates. They are typically found in intertidal zones. Some are found in deep sea, at depths up to six hundred and fifty feet or more.  Soft corals exist on inner reefs just below the stony corals. They are not often the dominant corals within the reef, inhabiting dim areas such as caverns. Soft corals are easily collected from the wild and most will thrive and grow quickly in captivity. Because of this, soft corals are popular for domestic aquariums.
Corals are not entirely self photosynthetic. They partner with autotrophs, internally symbiotic algae like zooxanthellae, to produce nutrients to sustain themselves. The symbiotic relationship between algae and coral is well-known: corals provide protection and algae performs photosynthesis to produce nutrients consumed by corals; however, the energy corals acquire from this symbiotic relationship is not enough for them to build biomass. Studies haves shown that corals mainly use this energy as fuel for respiration and mucus secretion, rather than using it as the main source for growth. Thus, corals also feed on other food sources like plankton, detritus, and dissolved molecules in the water column. 
For organic matter in the water, corals use their tentacles to trap small lives and pass them into their mouth. This is known as the “fly trap” mechanism and is generally utilized by corals with short tentacles; for corals with medium tentacles, they feed on small crustaceans and planktonic worms; and corals with large tentacles can feed on larger organisms including fish. Feeding for corals is essential because they acquire their necessary vitamins like fatty acids through this process. Corals’ feeding behavior varies depending on environmental cues like light, tides, currents, temperature, oxygen concentration, and food presence. When there is an absence of polyp predators, which is often at night, corals are more likely to “open up” to feed.  Studies have shown that soft corals mainly feed on phytoplankton since plant-digesting enzymes have been found in three soft coral species.
Soft corals can feed constantly. They are most known for getting their nutrients from multiple sources such as symbiotic relationships, planktonic organisms, microscopic food particles in the water, and dissolved organic matter. Many soft corals obtain the largest portion of their nutrients from symbiosis with the zooxanthellae. Some also have stinging cells, nematocysts, that sting passing organisms like plankton to make them easier to capture. Soft corals that are kept in captivity will thrive given plankton or brine shrimp. 
Soft corals are known to change forms to adapt with water flow patterns and types of prey. Some species, like the Xeniidae family, are known to exhibit a 'pulsing' motion. This happens when the polyps retract, extend, and retract again on the surface of the coral in order to capture prey. 
Soft corals have a chemical defense mechanism to ward off predators and other species that may harm them. They have allelopathic (toxic to other species) chemical effects; terpenoids and other molecules that poison creatures that wander onto its surface or try to attach onto the corals. They chemicals can be released into the water. 
Soft corals are able to reproduce sexually or asexually. They sexually reproduce when the corals release sperm and egg in a mass during a fertilizing event (brooding). The sperm that is released is gathered by female polyps that have eggs. When the egg and sperm fertilize their larva, it eventually settles to the bottom to begin life cycle.  Soft corals asexually reproduce by budding and fragmentation. Budding is when a new polyp develops out of a previous one. In fragmentation, a large healthy portion is cut away from the organism and begins growing and developing independently. Soft corals in captivity can be artificially propagated using the process of cutting and grafting. This involves cutting a reasonable piece of the coral off, soaking it in a sterile solution and attaching it with a kind of glue to a hard substrate. The coral will then adapt and grow on its own.
Soft corals are at danger from humans for reasons of disturbance like collection of corals for commercial and medical purposes. They are also effected by overfishing, pollution and discharge, and tourism.
Collection of Corals
In many countries, corals have been mined for commercial purposes by making pieces of corals into ornaments, souvenirs, or jewelry. Since soft corals are not only colorful and beautifully-shaped but also easy to grow in a given environment, they are also targets for the aquarium industry. Moreover, their tissues can be compounded to form medicines, thus they can also be collected for medical purposes. 
Overfishing results in increasing algae population that would block sunlight and out-compete corals. Overfishing of large predator fish also results in increasing population in polyp-feeding fish which would harm corals. Destructive fishing methods like dynamite fishing can have huge harmful effects on corals. Dynamite fishing refers to the fishing method that use explosives to bomb an area with a large population of fish and then collect dead fish afterwards. Those explosives would not only kill fish, but also destroy coral's skeletons and make it hard for corals to maintain their three-dimensional structure. 
Pollution and Discharge
Corals are affected by multiple pollution sources such as sediment, nutrients,runoff, groundwater seepage, and human changes in water sheds. Some pollutants that negatively affect corals are natural; however, are made worse by human influence. Examples of these are: high levels of rainfall; extreme weather events such as typhoons or hurricanes, highly erodible soils, and limestone hydrologic features. In addition to natural sources are many man-made sources: pesticides, petroleum hydrocarbons, pharmaceuticals, heavy metals, pathogens, and excess nutrients. Pollutants can damage coral reefs by blocking their access to nutrients or giving them a burst of too much nutrients, causing an excess of algae to suffocate the corals.
Soft corals draw in a lot of tourism, which is a threat to corals because recreational activities can severely damage coral. Recreational use of the coral reefs causes harm due to: breakage of coral colonies and tissue damage from direct contact such as walking, touching, kicking, standing, or gear contact; breakage or overturning of coral colonies and tissue damage from boat anchors; changes in marine life behavior from feeding or harassment by humans; water pollution, and trash and debris deposited in the marine environment. Reef Resilience says that, "Trampling of corals is also common on shallow, near-shore reef flats and has led to extensive damage in areas with high levels of human use." It is important for visitors of coral reefs to be informed and conscientious to the creatures and habitats below them. 
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