Atlantic and Gulf Rapid Reef Assessment

Coral reefs | Coral ID | Algae | Fishes

Coral Reef Background

 

 

Coral Reefs

Distribution and habitat requirements

Reef building corals are found throughout tropical and subtropical oceans such as the Indo-Pacific and Atlantic, normally between the Tropic of Capricorn and Tropic of Cancer (30S, 30N latitude). Reef development begins by settlement of reef forming organisms on a pre-existing hard foundation in shallow, warm well-illuminated water. The development of corals is influenced by such abiotic factors as light, substrate, wave forces, sediment, and temperature. Corals grow in areas with sufficient light and appropriate temperatures; light is essential for the symbiotic relationship between corals and zooxanthellae and the intensity of light affects the growth and nutrition of the coral. Optimal coral growth occurs when water temperatures are between 25-29C. Corals are often found along eastern shores of major land masses due to the presence of warm water flows. Abundance of corals decreases with increasing depth due to the extinction of visible light. They typically grow to depths <46m (150ft), although some species are found much deeper. The foundation of coral reefs is communities of hermatypic or reef building corals. Hermatypic corals are made up of tiny coral polyps that provide the calcium carbonate responsible for much of the structure of reefs. Corals belong to the phylum Cnidaria, best known for their possession of stinging organelles known as nematocysts. Distinguishing characteristics of cnidarians include radially symmetrical bodies, usually a crown of tentacles encircling the mouth, and a large hollow body cavity known as a coelenteron. Other cnidarians include sea anemones, jellyfish, hydroids, and sea fans. They exist as either free-swimming medusaE or as sessile benthic polyps. Polyps have columnar bodies topped with a ring of tentacles, a centrally located mouth leading to a gastrovascular cavity, and nematocysts. When feeding, cnidarians capture food using their nematocysts that either injects prey, becomes entangled in prey, or adheres to prey. Reef-building (or hermatypic) corals are of the order Scleractinia in the class Anthozoa. There are 6,000 species of anthozoans, all of them marine, although most do not make reefs and many zooxanthellate scleractininans do not get large enough to contribute significantly to reef construction.

 

Types of coral reefs

There are several major types of coral reefs in the Caribbean, each with a unique geological history and pattern of growth, including patch reefs, fringing reefs, bank/barrier reefs and atolls. Patch reefs are aggregations of a few corals isolated from other reefs by sandy areas or seagrrass beds. Fringing reefs closely follow shorelines sometimes with a narrow, shallow lagoon between the reef and land. Most Caribbean reefs are fringing reefs. Fringing reefs consist of several zones based on depth, structure of the reef, and algal and animal communities including the reef crest (the part of the reef the waves break over and usually at least partially emergent at low tide), the fore reef (the region of medium energy seaward of the reef crest). The spur and groove or buttress zone (the region of coral growth which includes rows of corals with sandy canyons or passages between each row) is part of the fore reef. Barrier reefs grow parallel to the coast, are often large and continuous, are separated from land by a wider lagoon, and are only likely to occur where there is a wide continental or insular shelf. The Great Barrier Reef in Australia is the largest barrier reef in the world. Atolls are circular shaped reef crests surrounding a central lagoon. In the Indo-Pacific, they develop during slow subsidence of volcanic islands and grow on the perimeter of the island, while in the Caribbean their origin is not understood as well.

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Anatomy of corals

A coral may consist of a single polyp or a colony of thousands of polyps that are linked by a common gastrovascular system through which they share food, water, and wastes with surrounding polyps. Coral polyps have tubular, saclike bodies with a ring of tentacles surrounding their mouths. Coral polyps can range in size from an average of 1-3 mm in diameter (for colonial corals) to 25 cm (in some solitary corals).

 A polyp is made up of two cell layers: the epidermis and the gastrodermis. The non-tissue layer between the gastrodermis and the epidermis is called the mesoglea. The polyp contains mesenterial filaments, which contain nematocysts, a pharynx, and the columella (central axis of corallite found below mouth). Nematocysts are also found in the tentacle tips. The coenosarc is soft tissue stretching over the surface of the coral between the polyps.


Adapted from NMITA1

 

The corallite is the part of the skeleton (corallum) deposited by one polyp and includes a skeletal wall (theca). Calcareous plate-like structures (septa) radiate from the wall to the center of the corallite. Other structures include the calice (the upper surface of the corallite), the coenosteum (the skeletal material underneath the coenosarc), and dissepiments (horizontal layers or partition of skeletal material (flat or curved) within or outside the corallite.

 


Adapted from NMITA1


Adapted from NMITA1

 

Eight morphological corallite characteristics used to classify and distinguish different coral species1:

Calice: cup-shaped depression on the corallite surface
Coenosteum(-a): skeleton between corallites within a colony
Columella(-ae): central axial structure (vertical rod) within a corallite
Corallite:
skeleton of an individual polyp, solitary or within a colony
Costa(-ae): extension of a septum beyond the wall
Dissepiment: horizontal partition (flat or curved) within or outside of corallite
Septum(-a): radially arranged vertical partition(s) within a corallite
Wall: vertical structure enclosing a corallite

 

1Adapted from: NMITA: Neogene Marine Biota of Tropical America, GLOSSARY OF CORAL MORPHOLOGIC TERMS by A.F. Budd and K.G. Johnson, http://poites.geology.uiowa.edu/database/corals/glossary/glossmnu.htm

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Coral reefs | Coral ID | Algae | Fishes

Robert N. Ginsburg
Atlantic and Gulf Rapid Reef Assessment
MGG-RSMAS, University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149
USA
Telephone: (305) 421-4664
Email: info@agrra.org
Send data to: data@agrra.org
URL: http://www.agrra.org

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