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of biological production in coral-reef assembly. It
is ironic that as early as 1888, Johannes Walther
(translated in Ginsburg
et al.,
1994) noted a dom-
inance of detrital material in Quaternary reefs
exposed along the Sinai Penninsula. This idea
was apparently ignored in favour of more-popular
'framework' models derived from the discussions
of Lowenstam and Newell, despite an apparent
recantation by the latter in Newell 1971. As we
swim over a modern reef, there is little disagree-
ment over its status. Less readily apparent is the
fact that the interiors of many (or possibly most?)
of these structures contain less than 30% recog-
nizable coral, with only a portion of that in place
(Conand
et al
., 1997; Hubbard
et al
., 1998). The
remainder is sand and rubble caused by ubiqui-
tous bioerosion plus void space. In as much as
this composition probably cannot by itself create
the rigidity that is the hallmark of 'true reefs', the
roles of encrustation and cementation must rise to
equal those of initial calcifi cation and subsequent
bioerosion.
of coral growth will be refl ected in trends in
reef accretion along the same gradient. Schlager
(1981) summarized available data for reef
aggradation relative to sea-level rise and coral
growth (Fig. 2). While accretion was an order of
magnitude slower in his model, it generally mim-
icked the rapid decrease of coral growth with
depth. Citing anecdotal data from other studies,
it was argued that most reefs in shallow water
have been capable of building at rates greater than
the maximum rate of glacio-eustatic sea-level rise
during the Holocene (
c
. 7 m kyr
1
). Based on this,
it was suggested that drowned reefs (or platforms)
in the ancient record represent a 'paradox' that
can be resolved only by invoking extreme and
short-lived conditions associated with either
rapid (and probably tectonically induced) sea-
level rise or degraded environmental conditions
(e.g. 'inimical bank waters' or larger-scale marine
'crisis events').
These concepts represent the foundation upon
which most current models of Holocene reef
development are based (Adey, 1978; Schlager,
1981; Macintyre, 1988). Linear-extension rates
of corals in shallow water can exceed 10 cm yr
1
,
but coral growth generally ranges from around
10 mm yr
1
in shallow water to less than 1 mm yr
1
at depth (for an excellent compilation, see Dullo,
2005). Reefs are thought to build at a rate roughly
an order of magnitude slower (Schlager, 1981;
Bosscher, 1992) but still following the general
depth-related pattern of coral growth (Fig. 3).
From this, it may be deduced that areas domi-
nated by branching coral will build faster than
those inhabited by slower-growing massive spe-
cies (Adey & Burke, 1976), while reefs in shallow
water will build faster than their deeper counter-
parts (Schlager, 1981; Bosscher, 1992).
Despite the overwhelming acceptance of these
axioms, they have never been systematically
tested. This paper attempts to quantify depth- and
species-related patterns of Caribbean and western
Atlantic reef accretion using a preliminary sur-
vey of information from the literature as well as
unpublished core data. It attempts to convince the
reader that the relationship between coral growth
and reef accretion is not as has been generally
assumed. More specifi cally, it is proposed that the
pattern that emerges from systematic analyses of
existing core data is controlled no more by coral
growth than by the myriad physical and biological
processes that come afterwards. If this is the case,
then it will have signifi cant bearing on existing
models of coral-reef accretion.
How are coral reefs built?
The symbiotic relationship between many corals
and their endolithic zooxanthellae, leads to
calcifi cation being strongly dependant on light
intensity and character ('photosynthetically active
radiation' occurs at the red end of the spectrum).
This relationship and the maximum depth for
corals have been generally understood since the
nineteenth century (Quoy & Gaimard, 1825).
Light and, therefore, photosynthesis decrease
exponentially with depth. Accordingly, the ratio
between light intensity (
I
) at any depth and the
light-saturating intensity (
I
k
: the amount of light
that will result in maximum photosynthesis) for
a particular coral species also drops. Chalker
(1981) proposed that photosynthesis by scler-
actineans can be approximated by this ratio and
the hyperbolic tangent function. Bosscher (1992)
showed that such relationships could be used to
predict the growth rate of corals with increasing
depth (Fig. 1).
It has been generally assumed that reef accre-
tion is a biological process that is dominated
by the growth of corals that are largely in place
or at least have not been moved far from where
they grew. While it has been long understood
that post-mortem degradation of corals is com-
monplace, it has been largely assumed that
much of the detritus from bioerosion will stay
within the reef, and that the depth-related pattern
