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Marine Laboratory Authors: Maricela YIP & Pierre MADL Headed by: dr.M.Stachowitsch and dr.W.Waitzbauer Vienna, October 7th 1999 |
Table of Contents:
Coral Anatomy Diseases acting with Pathogens Several diseases acting together Tissue Abnormalities |
1. Introduction: Pathogens of sleractinian corals have always been an essential tool to control dominating genera; thus, allowing less frequently occuring species to establish themselves in disease strucken areas. Diseases of reef building corals have increased significantly over the last decade and are causing widespread mortality. Studies have shown that coral diseases are affecting greater numbers of coral species, are increasing in frequency and distribution, and are spreading faster to new regions than ever recorded in the past. In recent years, there has been an emergence of newly described coral diseases with new types of pathologies or tissue conditions not observed in the past. Several of these diseases also have been recorded as killing coral tissue. Coral diseases occur in response to biotic and abiotic stresses. Biotic stresses are instigated by microorganisms including bacteria, fungi, viruses, and protozoans. Abiotic stresses occur in response to physical or chemical stresses, such as increased sea surface temperatures and UV radiation, anthropogenic input of nutrients, sediment, and other pollutants. Abiotic stresses may exacerbate the role of microorganisms in disease processes. Thus, the recent emergence of disease in corals is believed to be a consequence of deteriorating water quality that favors the proliferation of microorganisms, or of a reduced ability of a coral to defend itself against biotic and abiotic stresses. |
1.a A brief review about the functional elements of reef-building Corals: Many kinds of solitary corals or small coral colonies of anthozoans (phylum cnidaria) grow in temperate waters along marine shores, and even in the cold deep waters of the Arctic. However, the great majority of corals are scleractinian (stony) corals that construct tropical coral reefs (hermatypic - fig.1). Substantial reefs develop only in clear (excellent visibility), unpolluted (very little organic matter, or sediment), warm shallow or subtropical waters on firm substrates. They flourish best where the annual average temperature must not go below 18°C and the optimum temperature is 23°C to 26°C. Although, reefs in the Arabian (Persian) Gulf can survive enormous fluctuations in temperature from as low as 17°C in cold winter to up to 32°C in the summer. The process of skeleton deposition appears to be similar for different coral species, and it can be altered by environmental factors. Corals that live in deeper waters tend to form plate-like colonies, probably to maximize exposure of the symbiotic algae to available light, whereas in shallow waters the typical colony shape for the same species is more hemispherical. Wave action, sedimentation, and tissue injuries also contribute to shaping of the colony. |
![]() Fig.1 A healthy Reef (70kB) |
1.b Corals are of two types: perforate and imperforate. Perforate corals have porous skeletons with connections between the polyps through the skeleton. Imperforate corals have solid skeletons. Corals also have different growth forms. They can be placoid as in Tubastrea coccinea (orange cup coral) and Favia fragum (golf ball coral). They can also be meandroid in which corallites form a series within the same walls, as in the species Dendrogyra cylindrus (pillar coral). Other growth forms include coccoid, spherical shaped and phalecoid, as in Eusmilia fastigiata. | |
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![]() Fig.2 Coral Polyps (110kB) |
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![]() Fig.4 Zooxanthellae in a tentacle of a coral animal (left) and masses of zooxanthellae in the gastrodermal cells of a tentacle (right) (80kB) |
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