Octocorals

Soft Corals

Soft coral is also known as Alcyonacea and ahermatypic coral, which is a type of coral that does not secrete calcium carbonate skeleton or forms reefs. They are normally colorful and look like underwater plants that swing with the wave in the ocean. They are colonial, and often times little polyps combine together to form a large organism.

Structure and Biology

Skeleton

Soft corals have sclerites, which is a spiky skeleton element that supports their vertical structure as well as give them texture. They also has 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 different.

Suborders

Suborders of Soft Corals

Alcyoniina

Calcaxonia

Holaxonia

Protoalcyonaria

Scleraxonia

Stolonifera

Distribution and Habitats

Soft Corals can be found in waters world wide; however, 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.

Food Source

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 acquired 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.

For organic matter in the water, corals use their tentacles to trap small lives and pass them into their mouth. This is called “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 fishes. Feeding for corals is essential because they acquire their necessary vitamins like fatty acids through this process. Corals’ feeding behavior varies depending on 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.

In addition, dissolved organic matter (DOM) forms another important food source for corals. There are many types of DOM such as dissolved organic nitrogen and dissolved organic carbon. These DOM is found to be taken up by corals in high concentration during the day, which suggests that they are important sources for building organic matrix for corals, which is the protein around which calcium carbonate is deposited and it helps increase both the density and the strength of the coral skeleton.

Behavior

Soft corals can feed during the night or day. 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 marine algae, zooxanthellae. Some also have stinging cells, nematocysts, that sting passing organisms like plankton. Soft corals that are kept in captivity will thrive well being given plankton or brine shrimp.

Soft corals are known to often change forms so to adapt with water flows 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.

Reproduction

Soft corals are able to reproduce sexually or asexually. They sexually reproduce when the corals release sperm and egg in a mass all together as 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 allow to start 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.

Human Influence

Soft corals are at danger from humans for reasons of disturbance, over harvesting, habitat destruction, and pollution. Soft corals are harvested for recreationship purposes such as personal and commercial aquariums, and for medical purposes. The tissues can be compounded to form medicines. Soft corals draw in a lot of tourism, which is a threat because of people stepping on and damaging the corals.

Class Photos from the US/British Virgin Islands in the Caribbean

• Gorgonians