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MARINE LIFE of the Dominican Republic

Scuba diving and snorkeling are two of the most popular activities on a trip to the Dominican Republic. However before putting on your flippers or water tank, bear in mind a few general rules which are all part and parcel of being a responsible tourist:do not stand on the reef, touch it, remove pieces from it, or otherwise interfere with what you see.

Coral reef ecosystem as unique world heritage

Coral reefs are among the most diverse and productive ecosystems on Earth. They are found in the warm, clear, shallow waters of tropical oceans worldwide. Although coral reefs cover less than one quarter of one percent of the world's sea floor, they are home to 4000 different species of fish, 700 coral species and 1000 other plants and animals that depend on them for life. They provide over $30 billion in annual goods and services worldwide by enhancing biological diversity, fisheries production, maritime and cultural heritage.They are also a source of food, medicine and they act as shoreline barriers protecting the coast from wave damage, storm and erosion.Coral reefs with their beauty attract also tourists which boosts local economies. Coral reefs probably hold more beneficial undiscovered compounds. Humans will reap this benefit only as long as healthy coral reefs exist.

From Polyp to Reef

Corals are marine animals in the Phylum Cnidaria related to jellyfish and anemones. Coral animals are called polyps: tiny, cup-shaped, primitive marine organisms. Although some corals are a single animal, or polyp, most are colonial. Millions of polyps working together in a cooperative colony generation after generation create the limestone skeletons that form the framework of the beautiful coral reef. Most of this reef structure, the underlying foundation, is mainly composed of calcium carbonate from living and dead corals. The living corals build skeletons of calcium carbonate sequestered from the water. When the coral polyp dies, this skeleton remains incorporated in the reef framework. While corals are the chief architects of reef structure, they are not the only builders. Simultaneously many other organisms living in the reef community, other than corals, can contribute their skeletal calcium carbonate to the reef's structure in the same manner. Waves, grazing fish (such as parrotfish), sea urchins, sponges, and other forces and organisms break down the coral skeletons into fragments that settle into spaces in the reef structure. Although coral reefs look like solid structures, 40-70 percent of a reef is made up of tunnels, grottoes and caves. This open space provides more habitats than a solid structure. It takes years for some corals to grow an inch and they range in size from a pinhead to a foot in length.Since corals grow and provide the framework for extension of the reef  if corals are damaged then the whole complex equilibrium of the reef will be permanently altered. 

Coral growth physiology

The coral polyp is able to feed itself using stinging cells found on its tentacles which paralyze passing plankton. The plankton is digested but supplies only a small part of the nutritional requirements of the polyp. The remainder comes from the zooxanthellae. Zooxanthellae are critical elements in the continuing health of reef-building corals. Zooxanthellae are single-cell algae that live deep within the tissues of some corals. These symbiontic algae are able to convert sunlight, carbon dioxide and their own wastes into oxygen and carbohydrates. These carbohydrates are also used by the polyp to make calcium carbonate in a process known as calcification. This material forms the skeleton of the coral and eventually the framework of what we recognize today as a coral reef. The polyps, in return receive the "food" produced by the zooxanthellae. Through the exchange of nutrients, the zooxanthellae give the polyps their color, thus giving color to the reef.
This mutually beneficial relationship makes it possible for reef building corals to grow to their large size.Corals that do not contain zooxanthellae cannot produce massive coral reefs.

Corals are divided into two kinds and both are stationary on the ocean bottom. Hard corals. Also called reef-building corals, produce a rock-like skeleton made of the same material as classroom chalk (calcium carbonate). These skeletons and the various shapes of different colonies form the familiar structure of the reef. Hard corals rely on symbiotic algae (zooxanthellae) living within their tissues for nutrition and energy to build their skeleton. Most species form colonies composed of hundreds or thousands of polyps covering a stony skeleton such as brain, star, staghorn, elkhorn and pillar corals. These poplyps have rigid exoskeletons, or corallites, that protect their soft delicate bodies. The hard corals can be distinguished from the soft corals by the fact that hard coral polyps always have multiple of six tentacles, while soft corals have eight tentacles.
Soft corals. True soft corals, according to the definition, all belong to the subclass Octocorallia. The name "Octocorallia" refers to the fact that each polyp has eight tentacles. This can be confusing since many 'soft corals' are not actually soft. Soft corals, along with hard corals, are in the Phylum Cnidaria, having in common a very simple body plan and polyp structure. Most soft corals also lack a hard external skeleton, however, soft corals do produce smaller amounts of calcium carbonate that help them keep their shape. The outer crust contains spinicules of calcium carbonate, while the inner core consists of gorgonin; a flexible, fibrous wood- like protein. This gives the soft coral colony the ability to flex with the ocean waves and currents. Like hard corals, most soft coral species contain small single-celled algae (zooxanthellae) that live inside their tissues. The                  algae transfer food to the host coral.

Coral Species

Coral species have various distinct colors such as red, green, and blue. The color of coral changes depending on the condition of the health, even if it is a homogeneous colony in the same place. Generally, healthy coral has deep color, and becomes light when unhealthy. The coral health can be judged from its color by visual observation. The Coral Health Chart can be used specifically with:
Branching coral (Staghorn corals) 
Branching corals or staghorn corals belong to a genus of hard corals known as Acropora. There are different forms of growth, e.g., branching, cluster, bushy, finger-like, etc., that make up this diverse and popular genus of stony corals.Acropora corals grow relatevely fast in order to shade out other corals and gain more space on the reef. By growing branches staghorn corals provide greater exposure to sunlight for the symbiotic algae zooxanthellae that are hosted within their body, so they receive the majority of their nutritional requirements from photosynthetic algae that live within them. These corals are consummate reef builders and one of the most important members of coral reef communities around the world. They are found in a variety of colors.
Boulder coral (Star Coral, Bolder CoralBrain Coral, and Pineapple Coral) Sturdy, massive corals grow so slowly that they take hundreds of years to reach their enormous size. These photosynthetic brain-like or moon-like corals get their common name from a ring of tiny skeletal ridges that encompass each polyp. These corals are usually boulder-shaped. Boulder corals help to form the foundations of coral reefs.They are commonly found in shallow water such as intertidal reef flats or fringing reefs, rocky shorelines and harbour breakwaters
Plate coral (Montipora sp., Fungia sp.)
Plate Coral is a large polyp stony coral which grows in sheets or plates and can have whorls and interesting patterns resembling a flower. Those which belog to gen Fungia have a rounded flat skeletal disk with long                  tentacles extending from the top. These tentacles are frequently    brown or green in color, sometimes with brightly colored tips. Symbiotic algae zooxanthellae are hosted within this organism. On the reef these corals inhabit shallow areas in calm lagoons on sandy or muddy bottoms.
Soft coral
Gorgonians, or others such as sea fans, sea whips, and sea rods, sway with the currents and lack an exoskeleton and do not build reefs. While soft corals contribute in only a small way to the formation of the limestone structure of the reef, however they play an important role in reef ecology. Most soft corals contain the symbiotic algae zooxanthellae within their bodies, and receive nutrients from the algae when exposed to high light levels They occur commonly in all reef habitats. They display a dazzling array of bright colours and a wide range of colony shapes.The Coral Health Chart can't be used to monitor blue/purple corals or fire coral. The colour in these corals is associated with pigments and does not vary in bleaching events.

Types of reefs.

Together corals and other marine organisms construct many different types of reefs. The different types of reefs include:
Fringing reefs are reefs that form along a coastline. They grow on the continental shelf in shallow water.
Barrier reefs grow parallel to shorelines, but farther out, usually separated from the land by a deep lagoon. They are called barrier reefs because they form a barrier between the lagoon and the seas, impeding navigation.
Coral Atolls are rings of coral that grow on top of old, sunken volcanoes in the ocean. They begin as fringe reefs surrounding a volcanic island; then, as the volcano sinks, the reef continues to grow, and eventually only the reef remains.

Vital conditions

Several physical factors control and limit coral reef distribution. The growth rate of organisms that build coral reefs generally is affected by:
Temperature. Reefs do not develop in water temperature below 18º C/64º F. In water temperatures below 20º Celsius (C)/68º Fahrenheit (F), corals start to experience stress.
Light levels. The reef must be adequately unlighted. Heavy sedimentation smothers coral feeding structures and reduces the light for photosynthesis.
Salinity.Corals cannot tolerate significant deviations from the normal sea water salinity of 32-36 parts per thousand.
Depth. Since zooxanthellae need light for photosynthesis, most reefs grow in water 25 metres/80 feet or shallower. Although some corals can survive deeper, they cannot build reefs.
Nutrients concentrations and food supply.
Water quality. Increases in human populations in coastal regions near reefs mean increased construction and industrialization, resulting in siltation and turbidity from runoff and dredging activities, high levels of nutrients from sewage discharges, and the release of potentially toxic contaminants to nearshore waters.

Two related ecosystems are important to coral reef ecology:
Mangroves. These salt-tolerant trees with submerged rootstrap produce nutrients for food and habitat, stabilize the shoreline, and filter pollutants from the landbase.
Seagrass beds. They facilitate sediment settlement, stabilize the bottom and recycle nutrients to the coral reef.