Coral reefs are one of the most complex ecosystems on the earth and its estimated to support nearly 25 % of all marine life.
Coral reefs consist of hundreds and thousands of tiny (the size of a pinhead) invertebrate animals (having no back-bone) called polyps, they are the architects of the sea, living together in a colony. A new reef is formed when coral spawn, ie release clouds of eggs and sperm at the same time, the larvae travel with ocean currents to shallow water and attached to a solid surface, thus forming a thriving community with abundant animal life and plants, providing food, shelter and protection to thousands of individuals. The body structure of a polyp is very simple, you can imagine it like a tube closed on one end and where the polyp attachs to its growing surface for example a rock, a shipwreck.
More Coral info:
Each polyp has a mouth and a stomach (yes...they are animals, no plants or rocks !), around the mouth the tentacles (are found in sets of six or eight) are situated, which contains stinging cells which contain nematocysts, these cells produce toxins which are used to capture and immobilize the prey, such as plankton, small fishes to mention same. They have a dermis, which in contact with water and a gastrodermis inside the polyp, both tissues are separated by the mesoglea (jelly-like).
Mostly all hard coral polyps, have an algae inside called zooxanthellae, they have a symbiotic relationship, this occurs when two organisms create a union in which each is benefited by the other. Through photosynthesis the algae produces food transforming sunlight into nutrients and oxigen, the coral uses these products to make proteins, fats, and carbohydrates, and produce calcium carbonate (CaCO3) around them, in return the polyp gives the algae CO2, N2, other substances and a safe enviroment that the algae needs.
Now we can see why mostly of the coral reefs are found in shallow waters, as they require sunlight to survive.
The Zooxanthellae is also responsable for coral´s color, if the algae die then the coral turns white "coral bleaching" which is an unhealthy condition.
There are two types of corals, Hard or Stony Corals and Soft Corals:
Stony Corals are reef builders and have a hard skeleton, while Soft Corals dont produce skeleton their bodies are supported with clumps of crystallized calcitate (sclerites).
The skeletons of stony corals are secreted by the lower portion of the polyp by filtering Ca2+ and HCO3- from salt water, plus the CaCO3 they produce. This process make a cup (calyx) in which the polyp sits, they wall surrounding the cup is 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. Periodically, a polyp will lift off its base and secrete a new basal plate above the old one, creating a small chamber in the skeleton, where more CaCO3 is deposited elevating the coral.
When the Polyp is stressed or during the day, they contract into the calix to protec from predators, and since polyps are mostly nocturnal feeders, during the nigth they extends its tentacles to feed.
Corals reproduction can be sexual and asexual.
Fire coral, black and white corals, are not true corals, they belong to the same groups (celenterates) but they are Hydroids, they share the same body structure: dermis - gastrodermis and between these 2 layers of skin the mesoglea (jelly-like). Fire Corals are very similar to corals becouse they also have a calcium carbonate structure. These three hydroids have stinging cells, can inflict painful burning stings. Even a slight brush against it with bare skin will cause an immediate fiery reaction, raising painful welts that eventually itch for a long time. To avoid it, remember do not touch nothing and keep neutral buoyancy.
Reefs have an imperceptible growth ( only about few cm or inch per year !! between 5 and 25 millimeters, 0.2–1 inch) and an extraordinary fragility. Corals grow depending on water temperature, salinity, turbulence, and the availability of food.
Coral colonies can take amazing shapes, sizes and colors have a look at the pictures below. Please, take care !! overfishing, boat anchors, global warming, pollution, to mention some issues that affect to the reef, if you dive please remember:
How to protec the reef:
- Do not touch or harass any marine life (corals, fishes, etc)
- Do not buy any marine life souvenir like shells, sea stars, seahorses, coral jewellery, etc
- Keep neutral buoyancy
- Do not feed any underwater creature
- If takes photographs, dont hold from corals, practise your buoyancy control !
- Focus on your kicking, lift your fins up so you do not remove the bottom composition or break any coral
- When entering the ocean, think you are a guest ... take care of this amazing and fragile home !
- Think that you are not the only diver in the reef, if each diver touchs, harrass, feed, breaks, etc human hands will destroid the reef in the blink of an eye.
Note: Sponges are not corals, they are other kind of invertebrates which are also found in the reef.