Elizabeth K. Gocek
Tropical Marine Ecology
of the Bahamas and Florida Keys
June 1, 2000
In 1492, Christopher Columbus landed on the island of San Salvador, declaring it to be the “New World” for all to discover. Little did he know that the discovery would still continue today. The island itself contains a vast array of organisms that contribute to the ecosystem. However, the underwater world has as much, if not more, amazing life to explore. One such aspect of the water world of the Bahamas is the order of organisms known as Milleporina, Fire Coral. This organism is classified as coral, but is more closely related to jelly fish and other hydrozoans. They are not a true coral, but their abundance allows them to be a major contributor to the reef structure. The development of the order and survival make Fire coral a unique organism in the underwater ecosystem surrounding the Bahamian Islands.
Also known as stinging coral, false coral and itching coral, Milleporina are not a true stony coral. They are calcareous hydrozoans. Hydrozoans belong to the phylum, Cnidaria, known for possessing cnidocytes, stinging cells that are used to attack prey. Cnidocytes are also called nematocysts. This characteristic gives milleporina its trademark name, “fire coral”. A painful burning sting is produced if contact is made with a nematocyst. The skeletal structure is calcareous with a smooth surface. It may be textured and have tiny pores scattered on the coensteum, the surface of the skeleton. This characteristic gives Milleporina its name. Millepora translates to mean “many pores”. The pores are divided into two categories depending on their function for the organism. Gastropores are the location of the feeding polyps, known as gastrozoids. The polyps are small, containing four to six tentacles. The gastrozoids are hardly ever seen and rarely emerge from the pores. If they do emerge, they appear to be a fuzzy film on the surface of the coral. The internal structure of the gastropores contains zooxanthellae. These are the algae that maintain a relationship for the survival of both organisms. The algae in the pores help to promote production of calcium carbonate for the reefs to grow. As noted in the Ambergriscaye Field Guide, the mutualistic relationship between fire coral and zooxanthellae can be summarized by the following description:
Carbon dioxide is a waste product of the coral polyp respiration. Carbon dioxide
and water form carbonic acid. Carbonic acid dissolves or slows the deposition of
calcium carbonate by the corals. Carbon dioxide and water are the main ingredients needed in photosynthesis by the algae. The algae (zooxanthellae) remove the excess carbon dioxide and water within the coral polyp. This reduces the acidity (raises the pH) and creates and internal environment inside the coral, allowing the polyp to lay down its calcium carbonate skeleton. Only corals that harbour the algae can produce enough calcium carbonate to form the reef.
The other pores contain the tentacles that give fire coral its trademark name. Dactylopores house the visibly seen dactylozoids. Dactylozoids are mouthless polyps with short, thin stinging tentacles. There are usually five to nine dactylpores for every gastropore. The dactylopores are arranged around the gastropores. There are three types of nematocysts that can be found in the dactylopores: stenoles, isorhizaes and macrobasic mastigophores. Millepora species are the only cnidarians to possess the macrobasic mastigophores. These nematocysts are the reason why Millepora are classified into their own species. They are whip-like stinging cells used to attack prey. Nematocysts are the main defense mechanism and primary method of food capture for Milleporina. The stinging cells also help with territory accumulation by the species of fire coral. They often overcrowd other organisms and prevent them from overgrowing.
Fire coral mainly reproduce sexually. Medusae, possessing nematocyst buds are released into the water by the colony. Sex cells are formed then released and the medusae die. The planulae, free-swimming larvae, attach to a sessile area and form new colonies. Another option of reproduction is fragmentation of the main colony. This method requires large pieces of the original colony to break off and continue to survive in a new location.
Fire coral are often mistaken to be dead, making identification difficult. They appear dead because the tissues and polyps are often not visible. Also they do not have defined cups, like the true stony corals. The main visible characteristic of fire coral is the white edge across the tips of the branches. The rest of the structure usually is muted in color. Cream, brown, green and yellow are common colors. The most common is a mustard brown type.
Fire Coral is divided into three Caribbean species, Millepora alcicornis, Millepora complanta, and Millepora squarrosa. However, they all share a common evolutionary development. Two billion years ago in the Paleozoic Era, large-scale reef building began in layered structures. Stromatolites are the blue-green algae responsible for the framework of today’s coral reefs. At this time there were stable reef systems around the globe with mobile sea organisms inhabiting these areas. These organisms were called archaeocyathids. However, they were diminished 600 million years ago at the end of the Cambrian Period. All of these corals are presently extinct. 100 million years later in the Ordovician Period, calcareous sponges and bryozoans began a reef building cycle with other organisms and algae. At this point, coral had begun to flourish. Shallow seas were characteristic of the Silurian and Devonian period. During this time, 430-395 million years ago, coal became abundant in the shallow seas. Fish and coral populations grew and once again, a second major extinction of the coral species occurred. There was little survival of any reef organisms. The rise and fall of the corals continued with another emergence in the Carboniferous and Permian Periods (345 and 280 million years ago). Crinoids, starfish and bryozoans evolved. However another depletion of marine life occurred, wiping out over fifty percent of the existing families of organisms. The present day corals became more locally developed between the Atlantic and Pacific Oceans when the Isthmus of Panama completely closed between the two oceans, 1-6million years ago. This now accounts for the separate species of fire coral in the Pacific and Atlantic oceans.
Growth and development of coral reefs depend on numerous factors. Fire corals are usually found in slow to medium water movement, in clear well lighted areas. The most influential growth factors include water temperature, depth, light intensity, salinity, turbulence and sedimentation. The ideal temperature range is 20-28 degrees celsius. Temperatures below 20 degrees result in lack of growth. Temperatures above 28 degrees result in death of the zooanthellae. Higher temperatures also cause bleaching. Bleaching is the whitening of coral colonies when conditions are not viable for zooxanthellae. The calcium carbonate skeletons are exposed, resulting in a bleached look of the coral. “Some researchers feel that global warming will lead to widespread bleaching of corals, and could have a serous negative impact on marine biodiveristy. Reef growth ceases with a widespread breakdown in the algae/coral symbiotic relationship” (Scotty). Temperature is definitely a crucial factor to the survival of coral reefs. Coral reefs grown best in shallow water less than 25 meters deep. Salinity can vary from 18ppt (parts per thousand) to 70 ppt. Water turbulence needs to be mild. The more turbulent the water the higher the risk of physically breaking of the colonies. Fire coral, along with most other coral, are highly sensitive to environmental factors.
The area around Florida and the Bahamas that contains the Millepora species reside on a limestone ledge. The structure of the ledges provide the framework and gives some protection to help preserve the coral reefs. They are naturally threatened by weather systems, such as hurricanes and cyclones and ocean warming trends. However, they are also in danger of man made threats from pollution, sedimentation from coastal development and over-fishing. Recreation and tourism use also pose problems to reef structure and survival. Collecting for aquarium use and jewelry making impact the survival of reefs. Fire coral is not currently labeled as endangered or threatened, but the habitat is very sensitive to natural and human interruption and destruction.
Preservation of the coral reefs is not only important for the coral itself, but for the many organisms that live within the reef ecosystem. Biomedical research has also begun to reveal medicinal treatments dependent on inhabitants of the reefs. Sponges are currntly being studied as possible anti-cancer agents. “Compounds like didemnin B, diazonomide A, dolastatin 10 and discodermolide are all potential cancer fighting compounds and they are all derived from marine organisms which live within coral reef ecosystems” (ENN Daily News 4/9/97). Shells of crustaceans are rich in chitin that can be used to make sutures and bandages. Studies also show that coral reefs contain components needed to repair human bone by using calcium carbonate to form calcium phosphate. Not only could the destruction of coral reefs be devastating to the natural ecosystem of the oceans, but many organisms in the reef systems may have answers that will not be retrieved for human health, if destruction continues. Coral Reefs are a magnificent resource for beauty, aquatic richness and medical breakthroughs. Milleporina is a major contributor to the reef system of the Bahamian Islands.
It is up to our society to prevent human induced destruction and promote conservation of a major key to scientific advancement.
2. . http://coral.aoml.noaa.gov/bib/abstracts/author-l/lewisl.html
9. Wells, Sue, Hanna, Nick. The Greenpeace Book of Coral Reefs.Sterling Publishing Co., 1992
10. Roessler, Carl. The Underwater Wilderness: Life Around the Great Reefs. Chanticleer Press.
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