Unprecedented development along tropical shorelines is causing severe degradation of coral reefs primarily from increases in sedimentation. Sediment particles smother reef organisms and reduce light available for photosynthesis. Excessive sedmentation can adversely affect the structure and function of the coral reef ecosystem by altering both physical and biological processes. Mean sediment rates and suspended sediment concentrations for reefs not subject to stresses from human activities are < 1 to ca 10 mg cm-* d-' and < 10 mg I-', respectively. Chronic rates and concentrations above these values are 'hlgh'. Heavy sedmentation is associated with fewer coral species, less live coral, lower coral growth rates, greater abundance of branching forms, reduced coral recruitment, decreased calcification, decreased net productivity of corals, and slower rates of reef accretion. Coral species have different capabilities of clearing themselves of sediment particles or surviving lower light levels. Sedlment rejection is a function of morphology, orientation, growth habit, and behavior; and of the amount and type of se lment . Coral growth rates are not simple indicators of sediment levels. Decline of tropical fisheries is partially attributable to deterioration of coral reefs, seagrass beds, and mangroves from sedimentation. Sedimentation can alter the complex interactions between fish and their reef habitat. For example, sedimentation can lull major reef-building corals, leading to eventual collapse of the reef framework. A decline in the amount of shelter the reef provides leads to reductions in both number of individuals and number of species of fish. Currently, we are unable to rigorously predict the responses of coral reefs and reef organisms to excessive sedimentation from coastal development and other sources. Given information on the amount of sediment which will be introduced into the reef environment, the coral community composition, the depth of the reef, the percent coral cover, and the current patterns, we should be able to predict the consequences of a particular activity. Models of physical processes (e.g. sediment transport) must be complemented with better understanding of organism and ecosystem responses to sediment stress. Specifically, we need data on the threshold levels for reef orgarusms and for the reef ecosystem as a whole the levels above which sedimentation has lethal effects for particular species and above which normal functioning of the reef ceases. Additional field studies on the responses of reef organisms to both temgenous and calcium carbonate sediments are necessary. To effectively assess trends on coral reefs, e.g. changes in abundance and spatial arrangement of dominant benthic organisms, scientists must start using standardized monitoring methods. Long-term data sets are critical for tracking these complex ecosystems.

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Responses of coral reefs and reef organisms to sedimentation

This paper represents the results of more than 30 years field observations and research work carried out from the Isefjord Laboratory, Vellerup Vig (Zealand, Denmark), which is owned and financed by the author. The Isefjord complex, 36 km long, including the main fjord and the Roskilde Fjord, and covering about 400 km2, is a shallow (7–10 m, max. 30 m) area dominated by substrata of fine sand to mud with a high content of organic matter. As a guidebook for future research the first part gives information about distribution, systematics, ecology, and breeding of the majority of the 477 animal species described. Nearly 400 species are invertebrates and of the chordates 68 species are true fishes. 63% of all animal species have not previously been recorded from the area, 27 species are new to Danish seas, and one (Polychaeta, Capitellidae) is new to science. The hydrography is treated mainly on the basis of literature. The fjord system may be classified as mixohaline: the Isefjord proper is polyhali...

Systematics and ecology of the Isefjord marine fauna (Denmark) with a survey of the eelgrass (Zostera) vegetation and its communities

https://nsuworks.nova.edu/cgi/viewcontent.cgi?article=1332&context=occ_facarticles

Environmental Impacts of Dredging and Other Sediment Disturbances on Corals: A Review

The Effect of Sudden Changes in Temperature, Light and Salinity On the Population-Density and Export of Zooxanthellae From the Reef Corals Stylophora-Pistillata Esper and Seriatopora-Hystrix Dana

This study investigates the community structure of reefbulding corals in terms of species composition, zonation and diversity patterns, as well as possible factors affecting the observed distributions. The study was carried out by a series of line transects run underwater with SCUBA apparatus from the reef flat to a depth of 30 m. The reefs of Eilat are of the fringing type, with seleractinian corals as the most important hermatypic organisms. The different zones of the reef are analyzed on the basis of topographical characteristics of the reef, as well as from the numerical data on abundance and living coverage, using cluster analysis of all transects surveyed. The present knowledge concerning species diversity is reviewed and analyzed in the context of hermatypic coral data. Three different diversity indices (the species count, Simpson's index and Shannon and Weaver's index) were calculated for estimating the diversity obtained on different zones of the reef. It was found that there is a successive increase in diversity of hermatypic corals from shallow water to a depth of 30 m. Species diversity and living voverage of corals were significantly greater in steeper zones as compared to flatter zones of the reef. A possible explanation for this phenomenon is the accumulation of sediments in the flat zones. It is proposed that the severe and umpredictable nature of the reef flat may account for low abundance and living coverage of corals. It is also proposed that deep-water species which do not invade shallow water are species which have developed high specialization to their local environment. The idea that light intensity is a significant factor in calcium-carbonate deposition by scleractinian corals is supported by field measurements of individual colonies at different depths.

Alfred Goldsborough Mayer

Papers

Medusae of the World

Ctenophores of the Atlantic Coast of North America

Ecology of the Murray Island Coral Reef

Some Medusae from the Tortugas, Florida

Report upon the Scyphomedusae collected by the United States Bureau of Fisheries steamer "Albatross" in the Philippine Islands and Malay Archipelago