What is a Coral Reef

Date: Wed, 28 Aug 2013 20:45:11 -0400
From: John McManus <jmcmanus@rsmas.miami.edu>
Subject: Re: [Coral-List] FW: RE: What is a coral reef and where is
it’s edge?
To: <coral-list@coral.aoml.noaa.gov>
Message-ID: <007c01cea451$04b79750$0e26c5f0$@rsmas.miami.edu>
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In setting up the original, data-repository version of ReefBase, we had to
deal with a lot of conflicting definitions. We finally decided that there
were ‘true’ geostructural reefs, and informal ‘coral reefs’ which were coral
communities not associated with significant calcium carbonate deposition.
There were also ‘sub-reef units’ which include the ‘patch reefs’ to which
many refer, which are really bommies and coral patches within large reefs
such as atolls (there are also ‘real’ patch reefs not within other reefs).

As Veron pointed out in his plenary in the Japan ICRS, there is only a loose
relationship between coral reefs and corals. Corals grow on lots of hard
substrates, including fallen trees. Exposed bedrock supports lots of coral
communities in Ambon Bay (McManus and Wenno 1981 Bull Mar Sci). Similar
growths occur on sandstone substrates in Sri Lanka. Many coral communities
sit on boulders and lava flows. Tom Goreau Sr. and others used to
distinguish between true coral reefs and coral communities not on reefs.
Spalding et al. “Coral Reefs of the World” used the stricter definition of a
coral reef being wave-breaking, but extended their boundaries a bit to
broaden their area estimates. John Munro considered a “coral reef”  to be
bounded by the limits of where predatory reef fish would swim — the shelf
of Jamaica was one reef to him–including the large bank to the south. Both
Smith and Kleypas’ area estimates attempted to account for both
geostructural reefs and non-geostructural coral communities. This helps
explain why Spalding et. al estimated only half of what Smith and Kleypas
(in her best estimate) had estimated. Because of the wide ranging behavior
of some reef fish away from dense coral communities, John Munro had much
higher estimates for just the Caribbean.

Kleypas, McManus and Menez 1999 (Amer Zool) looked at the hundreds of coral
community and reef descriptions we had compiled in ReefBase, and found
geographic (and calcium carbonate saturation level) bounds to where
geostructural reefs were likely to have developed. Now that the saturation
levels are known to be changing, some people have incorrectly assumed that
many of those reefs are now dead — not accounting for the fact that huge
accumulations of calcium carbonate will take hundreds to thousands of years
to wear down under present conditions. Additionally, the limits were about
net deposition, not coral growth. There is now increasing evidence that reef
communities, sand and substrates can locally buffer the impacts of ocean
acidification (unless there is a shift to algal dominance), further slowing
the loss of these reefs (see recent papers by Anthony, Kleypas, and others).

Finding the ‘boundaries’ of a non-geostructural coral community is
fascinating problem I spent years pondering. I suggest using the ‘bounding
lines’ approach used in international Law of the Sea to define island
archipelagos and their internal waters. In other words, a definition of area
or perimeter would be meaningful for a particular size of bounding lines.

So, definitions are hugely important, and the misunderstanding of
definitions has been a major hold-up to the advancement of coral reef



John W. McManus, PhD.
Professor, Marine Biology and Fisheries
Director, National Center for Coral Reef Research (NCORE)
Rosenstiel School of Marine and Atmospheric Science (RSMAS)
University of Miami. Phone: 305-421-4814
Website: http://www.rsmas.miami.edu/people/faculty-index/?p=john-mcmanus
NCORE Website: http://ncore.rsmas.miami.edu/

“If I cannot build it, I do not understand it.” — Richard Feynman, Nobel