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National Oceanic and Atmospheric Administration

About Coral Reefs

Coral polyps

Coral reefs are complex, biologically diverse ecosystems. Countless studies, books and papers have been devoted to exploring and understanding the nature of these unique marine environments. These four essays discuss some of the most important aspects of coral reefs. Many of their physical and biological characteristics are discussed in detail. Coral reef threats, both natural and anthropogenic, also are explored.

These essays are not meant to be exhaustive. For more information, the reader can refer to the literature cited at the end of each essay.

What are Coral Reefs

Coral reefs are fragile, highly complex communities which have great biological and habitat diversity. Together, with adjacent and interrelated seagrass beds, mangrove forests, other substratum compositions, and their physical and chemical environments, they comprise the coral reef ecosystems which support well over a million species.

This essay begins with a general description of the individual coral animal. It provides an anatomical overview and notes unique cellular characteristics of these organisms. Major structural forms are discussed, as well as the range of environmental conditions necessary for reef survival. Geographic distribution and diversity of major reefs in the Pacific and Atlantic oceans is discussed, as well as the Darwin’s theory of atoll formation. The major biogeographic zones of typical reef systems are described. more detail

Coral Reef Biology

Reef building corals are sessile colonial organisms, meaning they spend their entire adult lives fixed to the same spot on the sea floor. Over time stony corals have evolved specific physiological and behavioral characteristics to exploit their environment. This essay presents an overview of the major reproductive, feeding, and competitive behaviors in many species of hermatypic (reef-building) corals. These include reproduction, with a focus on mass spawning events; the contributions of photosynthesis and carnivory in coral nutrition; and species interactions as they compete for free living space, often considered a major limiting factor on coral reefs. more detail

Deep Water Corals

This essay presents an overview of the solitary and colonial assemblage-forming corals that inhabit deep, cold waters, at lightless depths that may exceed 2000 m, and temperatures as cold as 4° C. Like the tropical, shallow-water coral reefs, these deep-water corals develop an infrastructure that provides habitat and reproductive grounds for a variety of commercial and non-commercial species of fishes and invertebrates. Discussed is the global distribution of known deep-water corals, particularly Lophelia and Oculina reefs and the threats, by human activities, to these fragile communities. Recently enacted protection and conservation measures are described. more detail

Major Reef-building Coral Diseases

During the last 10 years, the frequency of coral diseases appears to have increased dramatically. Most diseases occur in response to the onset of bacteria, fungi, and viruses. However, natural events and anthropogenic (human-caused) activities may exacerbate reef-forming corals' susceptibility to waterborne pathogens. This essay provides descriptions of the known major coral diseases under study. This includes: Black Band Disease, Coral Bleaching, Discoloring Spots, Rapid Wasting Disease, Red Band Disease, White Band Disease, White Plague Disease, White Pox Disease and Yellow Blotch/Band Disease. more detail

Hazards to Coral Reefs

This essay presents an overview of natural and anthropogenic factors threatening many reef systems. As human populations and coastal pressures increase, reef resources are more heavily exploited, and many coral habitats continue to decline. Most scientists believe reef degradation occurs in response to natural and anthropogenic stresses. In many cases, natural disturbances such as hurricanes, cyclones, or disease outbreaks are exacerbated by anthropogenic stresses, such as pollution, sedimentation, and overfishing. These can further weaken coral systems and compromise their ability to recover. Conversely, a reef directly or indirectly affected by anthropogenic stresses may be too weak to withstand a natural event. more detail

Coral Reefs Ecosystem Essays

CoRIS is offering a series of essays on coral reef ecosystems in United States jurisdictions in the Atlantic and Pacific Oceans, and the Gulf of Mexico. The essays give up-to-date information on the status and health of the coral reef ecosystems, and provide links to CoRIS-held metadata and data. An essay on the coral reef ecosystems of the Northwestern Hawaiian Islands (NWHI) is the first of this series. more detail