Done by: Abbas Mohammed

ID:080121023

The object of this volume is to describe from my own observation and the works of others, the principal kinds of coral-reefs, more especially those occurring in the open ocean, and to explain the origin of their peculiar forms. here I do not treat of the polypifers, which construct these vast works, except so far as relates to their distribution, and to the conditions favourable to their vigorous growth.

Reefs are concretions produced by living organisms.

Coral reefs are solid, long-lasting structures. Because they are formed by the hard parts of the animal skeletons.

Coral reefs have a salient topography. They are based on the sea floor on solid rock foundations

Coral reefs have ecological effects on their surroundings

The building blocks of coral reefs are the generation of reef-building, and other organisms that are composed of calcium carbonate. For example, as a coral head grows, it lays down a skeletal structure encasing each new polyp. 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. Many other organisms living in the reef community contribute their skeletal calcium carbonate in the same manner. Coralline algae are important contributors to the structure of the reef in those parts of the reef subjected to the greatest forces by waves (such as the reef front facing the open ocean). These algae contribute to reef-building by depositing limestone in sheets over the surface of the reef and thereby contributing also to the structural integrity of the reef.

Coral reefs and fishes in Papua New Guinea Southeast Asian coral reefs are at risk from

damaging fishing practices (such as cyanide and blast fishing), overfishing, sedimentation, pollution and bleaching. A variety of activities, including education, regulation, and the establishment of marine protected areas are under way to protect these reefs. For example, The risk of contamination of the waters of the Gulf Arab oil and industrial pollutants and civil based in several regions, and the disposal of sewage in the waters of the Gulf is increasing. Is also the poaching and the problems resulting from the establishment of towns and villages in high risk coastal Gulf.

Throughout the Earth history, from a few thousand years after hard skeletons were developed by marine organisms, there were almost always reefs formed by reef-building organisms in the ancient seas. The times of maximum development were in the Middle Cambrian (513-501 Ma), Devonian (416-359 Ma) and Carboniferous (359-299 Ma), due to Order Rugosa extinct corals, and Late Cretaceous (100-65 Ma) and all Neocene (23 Ma - present), due to Order Scleractinia corals.

Not all reefs in the past were formed by corals: in the Early Cambrian (542-513 Ma) resulted from calcareous algae and archaeocyathids (small animals with conical shape, probably related to sponges) and in the Late Cretaceous (100 - 65 Ma), when there also existed reefs formed by a group of bivalves called rudists; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.

Latitude ◦ The role of the temperature ◦ The effects of emersion ◦ The effects of sedimentation

Bathymetry◦ The number of coral species observed

decreases with the depth ◦ The coral production rates have also been found

to decrease with the depth ◦ The growth rates of the coral species decrease

with the depth,

Reefs are concretions produced by living organisms.

Coral reefs are solid, long-lasting structures Southeast Asian coral reefs are at risk

from damaging fishing practices Not all reefs in the past were formed by

corals The number of coral species observed

decreases with the depth

Harmelin-Vivien M, Stoddart DR (1985) Hurricane effect on coral reefs. Proc. Of the fifth Internat.

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