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Coral
Reef Science: Development Highlights
Habib
Sekha
U. E. Siebeck, N. J. Marshall, A. Klüter and Ove
Hoegh-Guldberg. Monitoring Coral Bleaching Using a Colour
Reference Card. Journal Coral Reefs. Volume 25, Number 3/August,
2006.
Communicated by Ecology Editor P.J. Mumby.
Abstract:
Assessment of the extent of coral bleaching has become an
important part of studies that aim to understand the condition
of coral reefs. In this study a reference card that uses differences
in coral colour was developed as an inexpensive, rapid and
non-invasive method for the assessment of bleaching. The card
uses a 6 point brightness/saturation scale within four colour
hues to record changes in bleaching state. Changes on the
scale of 2 units or more reflect a change in symbiont density
and chlorophyll a content, and therefore the bleaching state
of the coral. When used by non-specialist observers in the
field (here on an intertidal reef flat), there was an inter-observer
error of ± 1 colour score. This technique improves
on existing subjective assessment of bleaching state by visual
observation and offers the potential for rapid, wide-area
assessment of changing coral condition.
Comments:
The authors are referring to a chart which allows the determination,
semi-quantitatively, of the extent of coral bleaching. Other
similar charts have been available for several years in some
form or another. They are based on the fact that many corals
have beautiful pigmentation in their tissue that becomes visible
when their zooxanthellae density decreases due to bleaching
events. The zooxanthellae are colored different variations
of brown, which obscures the host's pigmentation. Hence, once
the zooxanthellae density decreases, the coral's pastel-like
colors become visible. In extreme bleaching events the coral's
tissue becomes white.
Keep in mind that these charts are typically designed for
use on corals in natural low-nutrient reefs, thereby showing
that pastel coloration is often a result of bleaching caused
by factors other than low nutrient levels. Pastel coloration,
therefore, might correspond with less than optimal coral health.
Here is an example of one such chart:
http://www.coralwatch.org/images/pdf/chart.jpg
More information is available on the following website:
http://www.coralwatch.org/default.aspx?page=details#reading
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