[Coral-List] Coral species list for Mesoamerican Barrier Reef System

[Derek Manzello]

Dear Alina,
	Thank you for bringing up the excellent reviews of Pam Hallock and Dennis
Hubbard.  I have read these chapters with great interest multiple times,
but in the interest of accuracy, I thought I would give them another
glance and share some pertinent points.  I found Hubbard’s chapter more
useful in terms of actual numbers and focus on modern reefs, but let’s
not discount Pamela’s great contribution.  One thing I’d like to point
out from Hallock’s paper is Fig. 2-7.  She differentiates between REEF,
fore- and back-reef (sediment aprons), and the lagoon.  Your 50% values
from the Jones and Endean volume specifically come from what she labels
“back-reef and lagoonal deposits.”  Based on the holistic definition of a
coral reef you provided, this leaves me to wonder if you consider Hawk
Channel in the Florida Keys a coral reef?  Ironically, Doug’s original
pontification noted that the Florida Reef Tract is not a true barrier
reef because it consists of a discontinuous string of outer bank reefs. 
Agreed, but does this not presuppose that the ‘reefs’ are the hard, rigid
structures and not the sediment fill in between?
	Now lets consider Hubbard’s review.  Dennis emphasizes the importance of
sedimentary infill within the reef framework structure, arguing that
coral reefs are not always made up of interlocking in situ coral
framework.  Rather, there has been a lot of ‘re-working’ of the
interlocking, original coral framework.  He reports that 60% of the CaCO3
production on a reef is reduced to sediment, with 41% of the coral
framework being made up of ‘recognizable’ coral, 45% is sediment, and 14%
void.  This led me to re-read his seminal CaCO3 budget for Cane Bay in
St. Croix (Hubbard et al. 1990), which is what a lot of this review is
based upon.  Specifically, based on these fractions, I was curious what
the makeup or origin of this sediment infill within the framework was. 
Keep in mind, this infill occurs within the rigid framework and not in
the lagoon or sediment channels/aprons, which he specifically discusses. 
Here are his numbers, which are quite revealing.  On average, there is
1.21 kg of CaCO3 produced per square meter per year at the reef in Cane
Bay.  1.13 kg of this annual total (or 93.4%) is from corals, 0.02 kg is
from coralline algae (1.7%), and 0.06 kg is from mollusks, forams, and
echinoderms (~5%).  Note that the production of CaCO3 by coralline algae
is TWO orders of magnitude less than that by the corals.  0.91 kg of the
total 1.21 kg CaCO3 produced per year ends up “in the reef”, whereas 0.30
kg is broken down to sediment.  Note that the 0.06 kg CaCO3/m2/yr they
measured for mollusks, forams, and echinoderms ends up exclusively in the
sand channels.  The remaining 0.24 kg of sediment that sits in the sand
channels has the following fractional makeup, which is different than the
50% number you threw out:  20% of the sand is mollusk, foram, echinoderm
(0.06/0.30), 6.8% is coralline algae – leaving nearly ¾ of the sand being
coral derived.
	Lets look at some pertinent quotes.  “While coralline algae cover a large
portion of the substrate, the much slower growth rates of corallines
relegates them to a secondary role as carbonate producers.  They
comprised only 6.8% of the reef derived sediment, found within in the
sand channels.” (Hubbard et al. 1990).  Note, this is the sand in the
sand channels, NOT what is retained within the reef matrix.  He very
specifically notes that the majority of this ‘sand’ is likely flushed
away by storms and is not preserved.
	Overall, Hubbard’s review is speaking primarily about the taphonomy of
the interlocking coral framework and how it is preserved in the rock
record.  He emphasizes that not only is coral growth vital to coral reef
construction/development, but that bioerosion, sediment transport, and
bio/chem Cementation are also important processes.  Amen to that. 
Directly, he says “The internal reef fabric is determined by (I) initial
CaCO3 production, (2) type/intensity of bioerosion, (3) patterns of
sediment storage within or removal from the reef, and (4) levels of
secondary cementation/encrustation.  MOST of the building blocks of the
reef started as coral, but they have been, to some extent, replaced by
multiple generations of boring, sedimentary infill, and cementation”
(Hubbard 1997).  However, to be fair, he does say “..careful examination
of many reefs reveals their rigidity is often dependent on secondary
overgrowth by CCA, bryozoans, and penecontemoraneous cementation as it is
on structural continuity afforded by a meshwork of in place framework.” 
Not surprisingly, there is no evidence provided for this latter
statement.
	In summary, I stand by my original contention that it is misleading and
inaccurate to claim that coral reefs are ‘coralgal” or algal-coral reefs.
 Saying that 50% of the reef is built by non-coral calcareous organisms
is fundamentally incorrect.  This leads people to think that algae are
just as important to the construction, development, and persistence of
coral reefs, which is not supported by a careful review of the actual
data.  Are algae important to coral reef dynamics?  Most certainly, and
we can divulge into a pedantic tangent citing all their important roles
if we desire to waste more time.  Do, or, have algae built modern coral
reefs.  No.  Only in rare cases have CCAs accumulated anything that could
be called a framework.  This occurs in locations where corals cannot live
like the very shallow, high surge algal ridge environments pointed out by
Macintyre.

Best,
Derek

Ref cited
Hubbard DK, Miller AI, Scutaro D (1990) Production and cycling of calcium
carbonate in a shelf-edge reef system (St. Croix, US Virgin Islands):
applications to the nature of reef systems in the fossil record. J. Sed.
Petrol. 60, 335-360.



--