Colored Dissolved Organic Material Increases Resiliency of Coral Reefs by Controlling Exposure to UVR

Document Type

Conference Proceeding

Publication Date



ICRS11, Ecosystem Assessment of Coral Reefs - New Technologies and Approaches, ultraviolet radiation, coral reefs, absorption coefficient, attenuation coefficient, CDOM


Although mass coral bleaching events are generally triggered by high seawater temperatures, experiments have demonstrated that corals and reef-dwelling foraminifers bleach more readily when exposed to high energy, short wavelength solar radiation (blue, violet and ultraviolet [UVR]: . ~ 280 - 490 nm). In seawater, colored dissolved organic matter (CDOM), also called gelbstoff, preferentially absorbs these shorter wavelengths, which consequently bleach and degrade the CDOM. Alteration and destruction of watershed and coastal wetlands have reduced natural sources of CDOM that are tidally flushed into reefal waters. We have measured absorption of UVR and UV irradiance at various reefs in the Florida Keys that differ in distance from shore and the degree of anthropogenic development of the adjacent shoreline. Our results show that reefs associated with intact shorelines tend to be exposed to lower intensities of UVR than reefs associated with developed shorelines. Absorption due to CDOM at 320 nm (ag320) was less variable at reefs associated with intact shorelines, and higher at inshore reefs compared to offshore reefs. UVR is attenuated more quickly at inshore than offshore, clear-water reefs at similar depths. Spectral slope of ag, S, was generally greater at offshore sites, indicating a higher degree of photo bleaching of CDOM.

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Citation / Publisher Attribution

Proceedings of the 11th International Coral Reef Symposium, v. 1, p. 579-583