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Open AccessArticle

Water Column Optical Properties of Pacific Coral Reefs Across Geomorphic Zones and in Comparison to Offshore Waters

1
Department of Marine Sciences, University of Connecticut, Groton, CT 06340, USA
2
Currently: Labsphere, Inc., North Sutton, NH 03260, USA
3
Bermuda Institute of Ocean Sciences, St. George’s GE 01, Bermuda
*
Authors to whom correspondence should be addressed.
Remote Sens. 2019, 11(15), 1757; https://doi.org/10.3390/rs11151757
Received: 20 June 2019 / Revised: 17 July 2019 / Accepted: 22 July 2019 / Published: 25 July 2019
(This article belongs to the Section Coral Reefs Remote Sensing)
Despite the traditional view of coral reefs occurring in oligotrophic tropical conditions, water optical properties over coral reefs differ substantially from nearby clear oceanic waters. Through an extensive set of optical measurements across the tropical Pacific, our results suggest that coral reefs themselves exert a high degree of influence over water column optics, primarily through release of colored dissolved organic matter (CDOM). The relative contributions of phytoplankton, non-algal particles, and CDOM were estimated from measurements of absorption and scattering across different geomorphic shallow-water reef zones (<10 m) in Hawaii, the Great Barrier Reef, Guam, and Palau (n = 172). Absorption was dominated at the majority of stations by CDOM, with mixtures of phytoplankton and CDOM more prevalent at the protected back reef and lagoon zones. Absorption could be dominated by sediments and phytoplankton at fringing reefs and terrestrially impacted sites where particulate backscattering was significantly higher than in the other zones. Scattering at three angles in the backward direction followed recent measurements of the particulate phase function. Optical properties derived from satellite imagery indicate that offshore waters are consistently lower in absorption and backscattering than reef waters. Therefore, the use of satellite-derived offshore parameters in modeling reef optics could lead to significant underestimation of absorption and scattering, and overestimation of benthic light availability. If local measurements are not available, average optical properties based on the general reef zone could provide a more accurate means of assessing light conditions on coral reefs than using offshore water as a proxy. View Full-Text
Keywords: Inherent Optical Properties (IOPs); coral reef; colored dissolved organic matter (CDOM); absorption; scattering; light ecology; remote sensing Inherent Optical Properties (IOPs); coral reef; colored dissolved organic matter (CDOM); absorption; scattering; light ecology; remote sensing
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MDPI and ACS Style

Russell, B.J.; Dierssen, H.M.; Hochberg, E.J. Water Column Optical Properties of Pacific Coral Reefs Across Geomorphic Zones and in Comparison to Offshore Waters. Remote Sens. 2019, 11, 1757.

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