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Thursday, August 14, 2008

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The island of Moorea (French Polynesia) is in a geographic area that facilitates reef growth. (Photo credit: Dr. Anthony Picciolo)
Reef-building corals are restricted in their geographic distribution. This is because the algal-cnidarian symbiotic machinery needs a narrow and consistent band of environmental conditions to produce the copious quantities of limestone necessary for reef formation. The formation of highly consolidated reefs only occur where the temperature does not fall below 18°C for extended periods of time. This specific temperature restriction -18°C- does not, however, apply to the corals themselves. In Japan, where this has been studied in detail, approximately half of all coral species occur where the sea temperature regularly falls to 14°C an approximately 25% occur where it falls to 11°C (Veron 2000). Many grow optimally in water temperatures between 23° and 29°C, but some can tolerate temperatures as high as 40°C for limited periods of time. Most require very salty (saline) water ranging from 32 to 42 parts per thousand. The water must also be clear to permit high light penetration. The corals’ requirement for high light also explains why most reef-building species are restricted to the euphotic (light penetration) zone, approximately 70 m (Lalli and Parsons, 1995).

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2:36 AM

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The skeletons of stony corals are secreted by the lower portion of the polyp. 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, calcareous septa (sclerosepta), which provide structural integrity, protection, and an increased surface area for the polyp’s soft tissues, extend upward from the basal plate and radiate outward from its center. Periodically, a polyp will lift off its base and secrete a new floor to its cup, forming a new basal plate above the old one. This creates a minute chamber in the skeleton. While the colony is alive, CaCO3 is deposited, adding partitions and elevating the coral. 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 (Barnes, R.D., 1987; Sumich, 1996).At other times, the polyp extends out of the calyx. The timing and extent to which a polyp extends from its protective skeleton often depends on the time of the day, as well as the species of coral. Most polyps extend themselves furthest when they feed on plankton at night.In addition to a substantial horizontal component, the polyps of colonial corals are connected laterally to their neighbors by a thin horizontal sheet of tissue called the coenosarc, which covers the limestone between the calyxes. Together, polyps and coenosarc constitute a thin layer of living tissue over the block of limestone they have secreted. Thus, the living colony lies entirely above the skeleton (Barnes, R.S.K. and Hughes, 1999).
This large healthy elkhorn coral (Acropora sp.) exhibits an arborescent branching pattern.
Colonies of reef-building (hermatypic) corals exhibit a wide range of shapes, but most can be classified within ten general forms. Branching corals have branches that also have (secondary) branches. Digitate corals look like fingers or clumps of cigars and have no secondary branches. Table corals are table-like structures of fused branches. Elkhorn coral has large, flattened branches. Foliose corals have broad plate-like portions rising above the substrate. Encrusting corals grow as a thin layer against the substrate. Submassive corals have knobs, columns or wedges protruding from an encrusting base. Massive corals are ball-shaped or boulder-like corals which may be small as an egg or large as a house. Mushroom corals resemble the attached or unattached tops of mushrooms. Cup corals look like egg cups or cups that have been squashed, elongated or twisted (McManus et al. 1997). While the growth patterns of stony coral colonies are primarily species-specific, a colony’s geographic location, environmental factors (e.g., wave action, temperature, light exposure), and the density of surrounding corals may affect and/or alter the shape of the colony as it grows (Barnes, R.D. 1987; Barnes, R.S.K. and Hughes 1999, Lalli and Parsons, 1995).

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2:33 AM

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Massive reef structures are formed when each stony coral polyp secretes a skeleton of CaCO3. Most stony corals have very small polyps, averaging 1 to 3 mm in diameter, but entire colonies can grow very large and weigh several tons. Although all corals secrete CaCO3, not all are reef builders. Some corals, such as Fungia sp., are solitary and have single polyps that can grow as large as 25 cm in diameter. Other coral species are incapable of producing sufficient quantities of CaCO3 to form reefs. Many of these corals do not rely on the algal metabolites produced by zooxanthellae, and live in deeper and/or colder waters beyond the geographic range of most reef systems (Barnes, R.D., 1987; Sumich, 1996).
Two images of the same solitary coral Fungia sp. On the left is a living organism showing its outer covering of living tissue, and clearly visible central mouth. The image on the right shows the underlying skeletal structure of the same organism with the outer covering of living tissue stripped away.

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2:31 AM

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Most corals, like other cnidarians, contain a symbiotic algae called zooxanthellae, within their gastrodermal cells. The coral provides the algae with a protected environment and the compounds necessary for photosynthesis. These include carbon dioxide, produced by coral respiration, and inorganic nutrients such as nitrates, and phosphates, which are metabolic waste products of the coral. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, they supply the coral with organic products of photosynthesis. These compounds, including glucose, glycerol, and amino acids, are utilized by the coral as building blocks in the manufacture of proteins, fats, and carbohydrates, as well as the synthesis of calcium carbonate (CaCO3). The mutual exchange of algal photosynthates and cnidarian metabolites is the key to the prodigious biological productivity and limestone-secreting capacity of reef building corals (Barnes, R.D., 1987; Barnes, R.S.K. and Hughes, 1999; Lalli and Parsons, 1995; Levinton, 1995; Sumich, 1996).
Healthy staghorn coral.
Zooxanthellae often are critical elements in the continuing health of reef-building corals. As much as 90% of the organic material they manufacture photosynthetically is transferred to the host coral tissue (Sumich, 1996). If these algal cells are expelled by the polyps, which can occur if the colony undergoes prolonged physiological stress, the host may die shortly afterwards. The symbiotic zooxanthellae also confers its color to the polyp. If the zooxanthellae are expelled, the colony takes on a stark white appearance, which is commonly described as “coral bleaching” (Barnes, R.S.K. and Hughes, 1999; Lalli and Parsons, 1995).

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2:29 AM

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All coral polyps share two basic structural features with other members of their phylum. The first is a gastrovascular cavity that opens at only one end. At the opening to this cavity, commonly called the mouth, food is consumed and some waste products are expelled. A second feature all corals possess is a circle of tentacles, extensions of the body wall that surround the mouth. Tentacles help the coral to capture and ingest plankton for food, clear away debris from the mouth, and act as the animal’s primary means of defense (Barnes, R.D., 1987; Levinton, 1995).While coral polyps have structurally simple body plans, they possess several distinctive cellular structures. One of these is called a cnidocyte—a type of cell unique to, and characteristic of, all cnidarians. Found throughout the tentacles and epidermis, cnidocytes contain organelles called cnidae, which include nematocysts, a type of stinging cell. Because nematocytes are capable of delivering powerful, often lethal toxins, they are essential to capturing prey, and facilitate coralline agonistic interactions (Barnes, R.D., 1987).

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2:27 AM

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Corals are anthozoans, the largest class of organisms within the phylum Cnidaria. Comprising over 6,000 known species, anthozoans also include sea fans, sea pansies and anemones. Stony corals (scleractinians) make up the largest order of anthozoans, and are the group primarily responsible for laying the foundations of, and building up, reef structures. For the most part, scleractinians are colonial organisms composed of hundreds to hundreds of thousands of individuals, called polyps (Barnes, R.D., 1987; Lalli and Parsons, 1995).
As members of the phylum Cnidaria, corals have only a limited degree of organ development. Each polyp consists of three basic tissue layers: an outer epidermis, an inner layer of cells lining the gastrovascular cavity which acts as an internal space for digestion, and a layer called the mesoglea in between (Barnes, R.D., 1987).

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2:22 AM

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Every year careless boaters run aground, destroying coral colonies that are hundreds of years old. Seen from the surface, reefs have a unique golden-brown color. If you see brown, you may be about to run aground. Be cautious when anchoring your boat. Do not deploy the anchor directly in coral. Usually there are sandy areas close by; anchor in the sand. Many popular reefs off Key Largo and at Looe Key National Marine Sanctuary have special anchor buoys for mooring. In these areas, tie up to the buoys, rather than anchoring. Do not dispose of trash, bilge washings and other debris on or near the reefs!
Florida coral reefs, with whom we share the seas, are significant, unique natural resources. Be a responsible visitor - insure the continued vitality of Florida's coral reefs

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2:22 AM

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The tropical setting in Florida's reefs attracts millions of visitors annually. In order to minimize human damage to the corals, everyone's cooperation is needed. The reefs are well marked on navigation charts; if you are not familiar with the area, refer to the charts.
When diving or snorkeling, look, but do not touch! Do not grasp, stand or sit on living coral. You may damage the coral and hurt yourself in the process. All coral is protected. It is against the law to collect, harvest or sell Florida corals in state and adjacent federal waters.
Visit the Southeast Florida Coral Reef Initiative for more information on what you can do to help protect coral reefs.

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2:20 AM

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Florida's coral reefs came into existence 5,000 to 7,000 years ago when sea levels rose following the Wisconsin Ice Age. Reef growth is slow; estimates range from one to sixteen feet every 1,000 years.
Stony corals are the major reef architects. Polyps, the living portion of the coral, extract calcium from seawater and combine it with carbon dioxide to construct the elaborate limestone skeletons that form the reef backbone. Coral polyps are united into colonies. An individual colony grows one-half to seven inches a year, depending on the species. Corals start life as free-living larvae that later settle on the sea floor and develop into massive, sedentary limestone formations.
Though reef corals are classified as animals, there is, in fact, a complex of microscopic plants that lives within the animal tissues (a symbiotic relationship). The animals benefit from the energy that the plants provide through photosynthesis. The plants are protected within the coral tissues and gain nutrients from animal wastes. These tiny plants are called zooxanthellae and are responsible for much of the color seen in reef corals.

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2:16 AM

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Platform reefs usually lie in sheltered seas and quite far offshore. They are flat-topped with small and very shallow lagoons.
Barrier reef

A coral reef growing parallel to the coastline and separated from it by a lagoon is called a barrier reef. The lagoon may develop between the fringing reef and the land. As the reef continues to grow further and further offshore it eventually reaches the edge of the continental shelf. Barrier reefs can also originate offshore if the depth of the seabed out there is shallow enough to allow corals to grow.
The most famous barrier reef is the Great Barrier Reef in Australia. It stretches over 2300 km and covers over 200'000 km2. It lies between 24 and 240 km from the main continent.
Atoll

Atolls are rings of reef, often encircling an island (sand and coral rubble). They typically have a shallow, sandy, sheltered lagoon in the middle. Access to the open sea beyond is through a number of channels. These provide fresh and colder water for the lagoons. Corals atolls are on the top of submarine mountains. These mountains are remnants of volcanos. Once there were fringing reefs around the volcano. As it slowly submerged the corals continued to grow up to the surface of the water. What remained after the volcano became invisible is a ring of coral reefs surrounded by deep ocean.
However some atolls were probably formed by rising sea levels rather by the sinking of islands. Other theories suggest that corals colonized eroded limestone formations, so called karstic saucers.

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2:15 AM

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Fringing reefs are relatively young. They can develop in shallow waters along the coast of tropical islands or continents. The corals grow upwards to sea level or just below and outwards towards the open ocean. Fringing reefs are generally narrow platforms a short distance from shore and don't contain a substantial lagoon.

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2:13 AM

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As with coral reefs around the world, Singapore reefs suffered a mass bleaching event in June 1998. Sea temperatures around Pulau Hantu and St John's were elevated by 1-2 deg C from March to June 1998. 50-90% of all reef organisms in Singapore were affected, particularly the hard corals, soft corals and anemones. The bleaching effect extended till 6m, the lower growth depth limit for coral growth locally. Sea temperatures returned to normal in August 1998. A study of the stressed colonies was undertaken during this period. 10 out of 35 coral colonies died from the stress, and the genera Sinularia and Euphyllia were most affected. Other colonies showed various signs of stress, such as growth of turf algae and silt accumulation, leading to partial mortality

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2:07 AM

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Careless diving or boating activities can severely damage fragile, slow-growing corals!!!

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2:05 AM

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The most significant cause of reef degradation in Singapore is sedimentation. Land reclamation, dredging of shipping channels and dumping of earth spoils, have increased the sediment load. Loss of coral reefs to land reclamation occurred along the southwest coast of the mainland and on some of the offshore southern islands. Increased sedimentation affected the remaining reefs in two ways 1) by causing a slow but steady reduction in live coral cover 2) by reducing the lower depth limit of coral growth on reef slopes. Surveys since 1986 indicated that live coral cover decreased by up to 20% on some reefs, although other reefs registered no impact. The reduction in sunlight penetration reduced the lower depth limit of coral growth. In the 1970s, coral growth extended to 10m down the reef slope. Today, growth is restricted to 6m although some coral species still occur at the 8m depth.
Accidental oil spills remain as an ever-present threat. However the 1997 Evoikos oil spill (27,000 tonnes) did not seriously affect coral reefs, although oil contaminated the upper parts of some reef flats.Other activities that also have an impact on the reefs include recreational and tourist-related use. Negligent or inexperienced divers without proper buoyancy control, leave a trail of broken corals. Anchor damage is caused by fishing boats and pleasure craft. At Pulau Hantu, a popular dive spot, courtesy mooring buoys were previously installed to prevent anchor damage.

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2:01 AM

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The reef can be subdivided into several zones: the reef flat, the reef crest and the reef slope. The shoreline gives way to the shallow reef flat that may vary in width and depth - at very low tides, some parts of the reef flat are exposed to air and direct sunlight. Here, scattered about are small colonies of boulder-shaped knob corals (Favia), maze coral (Platygyra sp.) and sponges of different colours. Pockets of sandy areas may be surrounded by lawns of large brown algae Sargassum sp. Bands of black sea urchins gather in large numbers. This level also marks the outer edge of the reef flat, which gives way to the reef crest.
Marine life on the reef crest is usually the richest - almost every type of coral is represented: the brain corals (Family Mussidae), bubble-corals (Family Caryophyllidae), pore corals (Family Poritidae), mushroom corals (Family Fungidae), cauliflower coral (Pocillopora sp), cave corals and disc coral (Family Dendrophyllidae), the table and staghorn corals (Acropora sp.), anemone corals (Goniopora sp)and many others. Living among these corals are many other marine animals. Deep purple-coloured sea anemones, with their symbiotic clownfish are a common sight. Crinoids (feather stars) are cryptic by day, and hide in coral crevices. Attached on the reef substrata are the sponges, sea squirts (tunicates), feather-duster worms and stinging hydroids. The other more mobile reef residents are the cowries, cone shells, nudibranchs, shrimps and crabs may be found in the crevices of the reef.

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1:55 AM

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THE MANY THREATS THEY ARE FACING

Human activity may represent the greatest threat to coral reefs living in Earth's oceans.
In particular, pollution and over-fishing are the most serious threats to these corals.
Physical destruction of reefs due to boat and shipping traffic is also a problem.
with the increase in human population and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially.

Markets for fishes and other natural resources have become global, supplying demand for reef resources far removed from their tropical sources.

Reefs are threatened well beyond coastal areas and so the problem is broader than factors from land development and pollution though those are too causing considerable damage.

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12:26 AM

Wednesday, August 13, 2008

I love you;

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9:08 PM