Corals

The Star Polyp Corals are also referred to as Starburst, Eight Tentacle, Mat, or Daisy Polyps. They are usually white or brown with a white dot in the center of each polyp, although, some more rare Star Polyps are green. The green specimens have been called Clavularia viridis; however, they are now identified as a Pachyclavularia sp. They have the distinctive eight-leaved tentacles on each polyp. They are colonial animals with several individual polyps attached to a piece of live rock.

Accurately described as an encrusting coral, Star Polyp Corals rapidly grow over adjacent rock work, coral, or even the glass of an established reef aquarium. They are a peaceful coral armed with the defensive capability of being able to retract or deflate each of their polyps in response to predation. They will not harm other corals that are placed close to their colony, but are susceptible to being damaged by any aggressive corals in the reef aquarium. They are easy to maintain in the reef aquarium and make an excellent candidate for the beginning through expert reef aquarist. They require a medium to high light level combined with a medium to strong water movement within the aquarium. For continued good health, they will also require the addition of iodine and other trace elements to the water.

The experienced hobbyist cultures the colony by taking a cutting from their encrusting base. The cutting is then glued to a hard substrate such as a rock or dead coral head.

The symbiotic algae zooxanthellae hosted within their bodies provide the majority of their nutritional requirements through photosynthesis. They also benefit from weekly feedings of micro-plankton or foods designed for filter feeding invertebrates.

The Plerogyra Bubble Coral is a large polyp stony (LPS) coral and is also referred to as a Grape, or Octobubble Coral. Its genus name, Plerogyra, comes from the Latin pleres (full) and gyros (wide circle), which describes the round or oval, bubble-shaped polyps resembling a cluster of grapes when open during the day. It is an aggressive coral with long sweeper tentacles that will sting corals that are placed in close proximity to it in the reef aquarium. It can also sting the reef aquarist who tries to handle it when its sweeper tentacles are out, so precaution should be taken.

It requires a low to medium light level combined with a low to medium water movement within the aquarium. For continued good health, it will also need the addition of calcium, strontium, and other trace elements to the water.

It will benefit from additional food fed weekly in the form of brine shrimp or micro-plankton.

Corals are a part of the group of small aquatic animals called "Cnidarians." Cnidarians include the corals, sea anemones, hydroids, and jellyfish. Some are motile (free-swimming), like the jellyfish and hydroids, and others are sessile (attached), like the corals and sea anemones. Corals are a very diverse group of Cnidarians. They are made up of many tiny organisms living together in a colony, and each individual organism is called a "polyp."

What is a coral polyp?

A polyp is a small marine invertebrate (spineless) animal. Some coral polyps are as small as the head of a pin and others can be as large as a foot in diameter, but the majority of them are small. A polyps' body has radial symmetry, which means that if a line were drawn any way through the middle of the body, it would produce two identical halves. The body structure is simple – it is shaped like a tube. The tube is closed on one end where the polyp attaches to its growing surface. The other end of the tube is the mouth, which is used for both taking in food and excreting wastes. Tentacles surround the mouth for gathering food, and are usually found in multiples of six or eight. The body tissues of polyps are extremely simple, with only two cell layers – the outer epidermis, which has direct contact with the water, and the inner gastrodermis. The space between the two cell layers is filled with a jelly-like substance called "mesoglea."

The epidermis contains many different kinds of cells that perform separate functions.

Nematocysts: These are are arrow-like barbs on the tentacles that are filled with toxins. These toxins paralyze the microscopic crustaceans and other organisms that the polyp feeds on, while serving to protect the polyp from attack by predators. If the toxins are strong enough, they can even deter growth of other corals, and the stronger coral will have an advantage in competing for space to grow.
Epitheliomuscular cells: The second type of specialized cells in the epidermis are the epitheliomuscular cells that have muscle fibers for movement and contraction of the polyp.
Sensory receptors and primitive nerve cells: These allow the organism to gather and process information about its surroundings.
Mucus-producing cells: A very important job of some of the cells in the epidermis is to produce and secrete mucus. These mucus cells help to clean and protect the organism by removing dirt and other particles that may settle on the coral.
Interstitial cells: These cells may later turn into one of the specialized cells described above, or they can also play a roll in reproduction by differentiating into sperm or egg cells.

Similar to the epidermis, the gastrodermis also has different kinds of cells and structures. There are however, only two major types – glandular and epitheliomuscular.

Glandular cells: The glandular cells secrete digestive enzymes into the cavity in the center of the tube-like polyp. This cavity is a very primitive stomach, and is called the "gastrovascular cavity." The digestive enzymes break down the food that the organism eats into smaller pieces.
Epitheliomuscular cells: The epitheliomuscular cells function to move and contract the organism. In the gastrodermis they also have the important role of ingesting the small particles of food that have been broken down by the digestive enzymes. For this reason, they are known as "nutritive muscular cells." The food is then further digested inside the cells and broken down into components the cells can use to grow and function. The nutritive muscular cells also have flagella on them that help to mix the food inside of the gastrovascular cavity.
Mesenterial filaments: Mesenterial filaments can be found in the gastrovascular cavity. These long, thread-like structures contain digestive enzymes, and sometimes nematocysts. The filaments can be expelled through the mouth at the approach of food, or as offensive weapons against neighboring corals.
Zooxanthellae: In some species, the gastrodermis is also home to zooxanthellae (zo-zan-THEL-ee), a type of unicellular algae. The zooxanthellae live inside the gastrodermal cells of coral in what is called a "symbiotic relationship." In this type of association, two organisms live in close proximity and at least one of the organisms benefit from the relationship. In the case of coral and zooxanthellae, both organisms benefit from their living arrangement. The zooxanthellae are photosynthetic organisms; they capture sunlight and turn it into energy-rich compounds, which can be transferred to the cells of the polyp. Like all plants, the zooxanthellae need certain nutrients, such as nitrogen and phosphate, to survive and continue photosynthesis. The concentration of these compounds in ocean water is very small, and the zooxanthellae acquire them from the polyp. The polyp obtains these essential nutrients through the plankton and other food it eats. The zooxanthellae are also responsible for the color of the coral. If the zooxanthellae die, the coral turns a white color, called "coral bleaching," and is a very unhealthy condition. Though the zooxanthellae and some coral polyps can survive independent of one another, it is much more efficient for them to work together, and they are able to grow much faster if they cooperate.

How are corals classified?

There are many ways to classify corals – soft vs. hard; hermatypic (reef-building) vs. ahermatypic (non-reef-building); or those with zooxanthellae vs. those without zooxanthellae – but the main distinction is between hard and soft corals.

What are soft corals?

Soft corals are those that do not have hard skeletons or build reefs. Common examples include sea fans, sea whips, leather corals, and tree corals. Soft corals with zooxanthellae are often recommended for beginners in marine aquarium keeping. Only a minority of soft corals rely on zooxanthellae, however. Since the algae need intense sunlight to photosynthesize, the corals that do not have zooxanthellae are able to live at greater depths and in murkier water. Essentially, they can survive anywhere there is enough plankton to sustain them. Since the soft corals do not produce the skeleton that hard corals do, their body tissue is supported with clumps of crystallized calcite called "sclerites." The sclerites are suspended in an inorganic matrix and give the tissues support, while still allowing a lot of flexibility. The sclerites come in many shapes and sizes, and the shape of the sclerites is often an important clue in the identification of a soft coral.

What are hard corals?

Hard corals are those responsible for building coral reefs. There are very few hard corals that are ahermatypic. Those that are do not contain zooxanthellae, but hermatypic corals always contain zooxanthellae. Reefs are therefore located in shallow, clear water where there is the most direct sunlight to facilitate photosynthesis in the algae. Reefs are magnificent and beautiful ecosystems that cover less than 0.2% of the ocean floor, yet they are estimated to support nearly 25% of all marine life. For example, a specimen of coral measuring only 25 centimeters in diameter was found to have ten fish, at least twenty crustaceans, several shrimp, mussels, snails, and a pair of gall crabs living in its branches. This is not to mention the many microscopic parasites and other symbiotic organisms that were also living on or in the coral.

The polyps of hard corals make a sturdy, protective shell out of calcium carbonate. They filter the bicarbonate and calcium ions out of the seawater, where they are in abundance. The lower portion of the polyp secretes the skeleton where it is attached to a rock or other hard surface. This process produces a cup, called the "calyx," in which the polyp sits. The walls surrounding the cup are called the "theca," and the floor is called the "basal plate." Thin septa arise from the basal plate and provide the polyp with increased surface area, structural integrity, and protection. When polyps are physically stressed, they contract into the calyx so that virtually no part is exposed above the skeletal platform. This protects the organism from predators and the elements.

Many polyps are nocturnal feeders – retracting into the protection of the calyx during the day and extending their tentacles at night to feed. The calyx and polyp together are called a "corallite." The calyxes are connected to one another by more skeletal material called "coenosteum." The polyps also have living tissue connecting them called the "coenosarc," which lies on top of the coenosteum. The entire living tissue, therefore, lies on top of the skeleton. The polyps are able to share nutrients with one another through the coenosarc. When one polyp obtains food, it is shared with all the others.

Reefs grow very slowly. They only grow approximately one inch per year, but that is efficient enough to surpass decomposition by natural means. Unfortunately, there are other "unnatural" factors that can tear down the reef, such as overfishing, harmful fishing practices, damage from boat anchors, dredging, global warming, pollution, runoff and sedimentation from deforestation, as well as other human disturbance. There are many conservation groups working to protect these unique environments by preventing human destruction of the reefs. Organizations such as Reef Relief, MAC (Marine Aquarium Council), Reef Check, IMA (International Marinelife Alliance), USCRTF (U.S. Coral Reef Task Force), CORAL (Coral Reef Alliance) and CORL (Coalition of Reef Lovers) are just a few of the key groups that are providing resources and plans of action in order to help manage and protect our beautiful coral reefs.

Coral colonies can take many fascinating shapes and sizes. They can resemble fingers, mushrooms, tree-branches, elk horns, cups, and even brains. They can be as small as a dime or as big as a room, and come in many brilliant colors. Their extraordinary diversity and importance to marine ecosystems makes them a life form we should enjoy, appreciate, and protect.

Red Mushroom

Actinodiscus species

(31 Oct 03 - Jeffs Exotic Fish)

Also known as: Mushroom Sarcophyton Leather, Elegant Leather Coral, Green Crown Leather, Mushroom Coral, Mushroom Leather Coral, Toadstool Leather Coral

Finger Leather, Lobophytum

Lobophytum species

Also known as: Sinularia Finger Thick, Finger Leather Coral, Devil's Finger Leather Coral

Button Polyp

Epizoanthus species

Also known as: Sea Mats, Moon Polyps, Encrusting Anemones

Yellow Zoanthid

Cnidaria; Anthozoa: Zoanthidea

Also known as: Disc Anemones, Flower Corals, Mushroom Anemones