[Coral-List] What is a coral reef and about "geological reef"?

Dennis Hubbard dennis.hubbard at oberlin.edu
Thu Nov 3 14:40:26 EDT 2016

Thanks Doug:

This is why I tell students that I only discuss "what is a reef" with good


On Wed, Nov 2, 2016 at 3:59 PM, Vassil Zlatarski <vzlatarski at gmail.com>

> Dear colleagues,
> Hope the end of the exchange concerning "geological reef" and a text from
> coming book referring "What is a coral reef" are of interest.
> Cheers,
> Vassil
> 8:23 PM (15 hours ago)
> to Eugene, me
> Indeed, that has been my view until recently.  Problem is, people,
> including me, commonly refer to "reefs" or "coral reefs" and make
> statements like "reefs are all going to (or not going to) die in a few
> decades."  Or "coral reefs will disappear (or not) by 2100".  Reading or
> hearing those, they do not tell you whether the author is saying that the
> coral reef ecosystem will die or disappear, or whether the carbonate
> buildup will die or disappear.  Yet obviously, the carbonate buildup, which
> is what a reef is, will not die or disappear in our lifetimes.  It was
> never alive in the first place, and it won't disappear any time soon.  The
> corals could, and the coral reef ecosystem, could die.  But the way we use
> the terms, we have to guess which one the author meant, and many people
> haven't been making the distinction, and I think they are very different
> systems, with very different time courses and processes.  Related, yes,
> dependent on each other, yes, intermingled (life in holes), for sure.  But
> you can easily have one without the other.  Fossil reefs on land, and
> carbonate caps on guyotes have cabonate buildups originally produced by
> coral reef ecosystems, but no living reef building corals. "Coral
> communities" on terrestrial rocks, have live corals and many other
> organisms, but not carbonate buildups.  They are usually associated, but
> they are separable.  I think we need to distinguish them.  I probably
> shouldn't have written "geological reefs", maybe coral-ecossytem-produced
> carbonate buildups would be better, maybe there is another term.  But
> "reef" or "coral reef" is commonly used for either or both, and I think we
> need to distinguish them.   Cheers,  Doug
> On Tue, Nov 1, 2016 at 9:08 AM, Eugene Shinn <eugeneshinn at mail.usf.edu>
> wrote:
> > Thanks, Yes I forgot worm reefs. Over the years there have been sessions
> > at national geological meeting having to do with "What is a reef" Nothing
> > ever got resolved So I finally decided I would not worry about it very
> > much.
> >
> > On 11/1/16 2:27 PM, Douglas Fenner wrote:
> >
> > I like it!  Clear.  I'd just add that the ecological community that
> > produces the reef is a distinct thing from the reef itself.  The
> ecological
> > community can die, but the reef can't.  The reef can exist whether it is
> in
> > the water or out.  Ah, you forgot one kind of reef, "worm reefs."  Also,
> > there is the question of deep coral reefs.  They are clearly bioherms,
> but
> > deep coral reefs never get near to the surface.  So by the navigator
> > tradition they are not reefs, though they are coral reefs for sure, just
> > not zooxanthellate coral reefs, rather they are azooxanthellate coral
> > reefs.
> >      I remember that there was an article published on defining coral
> > reefs several decades ago, but have been unable to find it.
> >     Cheers, Doug
> >
> > On Tue, Nov 1, 2016 at 7:08 AM, Eugene Shinn <eugeneshinn at mail.usf.edu>
> > wrote:
> >
> >> Doug, I just finished the final touches on a requested book I am doing
> >> with Barbara Lidz for the University Press of Florida. We include in
> chapt
> >> 4 a discussion of what a reef is and is not. The  title of the book is
> >> "Geology of the Florida Keys: A Natural Laboratory" Below is our
> section on
> >> that subject. Best Wishes, Gene
> >>
> >> Before proceeding, we should ask an age-old question, “What is a reef?”
> >> More specifically, “What is a coral reef?” This seemingly simple
> question
> >> lacks easy answers. Answers remain fuzzy and divided and are confused by
> >> maritime history and lore. The traditional sailor’s term for reefs
> includes
> >> any topographic feature upon which a vessel may become grounded.
> Because of
> >> this vagueness, areas such as submerged rocks or mountaintops can be
> called
> >> reefs. For example, “Bligh Reef,” on which the 274-m (900-ft) EXXON
> >> *Valdez* oil tanker grounded on March 25, 1989, is simply a submerged
> >> mountaintop—not a true reef. Sand bars have also been called reefs. For
> the
> >> purposes of geology, a more precise definition has long been debated,
> yet a
> >> precise one remains elusive. Geologists lean toward organically created
> >> topography, often called bioherms in geologic literature. The key
> >> distinction hinges on whether a topographic feature is created by
> growth of
> >> an organism rather than a non-living object. Thus, there are oyster
> reefs,
> >> sponge reefs, bryozoan reefs, stromatolite reefs, algal reefs, rudistid
> >> reefs, and so forth. A sand pile is not a reef. In the Florida Keys, we
> are
> >> concerned mainly with reefs built by corals. On the other hand, there
> are a
> >> few cases where mud banks capped by branching corals have been called
> >> reefs.
> >>
> >> --
> >>
> >>
> >> No Rocks, No Water, No Ecosystem (EAS)
> >> ------------------------------------ ------------------------------
> -----
> >> E. A. Shinn, Courtesy Professor
> >> University of South Florida
> >> College of Marine Science Room 221A
> >> 140 Seventh Avenue South
> >> St. Petersburg, FL 33701<eugeneshinn at mail.usf.edu>
> <eugeneshinn at mail.usf..edu>
> >> Tel 727 553-1158
> >>
> >>
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Dennis Hubbard
Chair, Dept of Geology-Oberlin College Oberlin OH 44074
(440) 775-8346

* "When you get on the wrong train.... every stop is the wrong stop"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"

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