Detecting Detrimental Change in Coral Reefs (!)

[OKIsItJustMe]

(Please note, NASA publication, copyright concerns are nil.)

http://www.nasa.gov/topics/earth/features/coral-damage.html

[font face=Times,Times New Roman,Serif][font size=5]Detecting Detrimental Change in Coral Reefs[/font]
01.26.12

[font size=3]Over dinner on R.V. Calypso while anchored on the lee side of Glover’s Reef in Belize, Jacques Cousteau told Phil Dustan that he suspected humans were having a negative impact on coral reefs. Dustan—a young ocean ecologist who had worked in the lush coral reefs of the Caribbean and Sinai Peninsula—found this difficult to believe. It was December 1974.


[font size=1]The Pinnacle III reef in Discovery Bay on the north coast of Jamaica four days after its Sept. 16, 1972 discovery. The pinnacle reef rises some 110 feet from the seafloor. At the time of its discovery the reef was completely covered with corals and large tree-sized seafans. Credit: Phil Dustan.[/font]

But Cousteau was right. During the following three-plus decades, Dustan, an ocean ecologist and biology professor at the University of Charleston in South Carolina, has witnessed widespread coral reef degradation and bleaching from up close. In the late 1970s Dustan helped build a handheld spectrometer, a tool to measure light given off by the coral. Using his spectrometer, Dustan could look at light reflected and made by the different organisms that comprised the living reefs. Since then, he has watched reefs deteriorate at an alarming rate. Recently he has found that Landsat offers a way to evaluate these changes globally. Using an innovative way to map how coral reefs are changing over time, Dustan now can find 'hotspots' where conservation efforts should be focused to protect these delicate communities.

A Role for Remote Sensing

[font size=1]Left: A Landsat pixel-based map showing where the most change has been detected on Caryfort Reef between 1984 and 1996. Right: The spine of elevation shows where the most change has occurred, for Carysfort this change has been correlated with coral decline. Credit: Phil Dustan.[/font]

Situated in shallow clear water, most coral reefs are visible to satellites that use passive remote sensing to observe Earth's surface. But coral reefs are complex ecosystems with coincident coral species, sand, and water all reflecting light. Dustan found that currently orbiting satellites do not offer the spatial or spectral resolution needed to distinguish between them and specifically classify coral reef composition. So instead of attempting to classify the inherently complex coral ecosystem to monitor their health, Dustan has instead started to look for change—how overall reflectance for a geographic location varies over time.

Dustan uses a time series of Landsat data to calculate something called temporal texture¬—basically a map showing where change has occurred based on statistical analysis of reflectance information. While Dustan cannot diagnosis the type of change with temporal texture he can establish where serious changes have occurred. Coral communities have seasonal rhythms and periodicities, but larger, significant changes show up as statistical outliers in temporal texture maps and often correlate with reef decline.

A Case Study


[font size=1]There was a 92 percent loss of living coral on Carysfort between 1975 and 2000. Credit: Phil Dustan[/font]

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(More depressing information and larger images at the link…)