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Hutchings, 1994; Tribollet
et al
., 2002), and the
Caribbean (Stearn & Scoffi n, 1977).
A quantitative assessment of bioerosion rates
across the full depth range of modern reefs is not
available. However, anecdotal information is avail-
able that may allow at least a qualitative character-
ization of depth-related patterns. In shallow water
off Barbados, Scoffi n
et al.
(1980) noted increased
bioerosion in shallower water, owing to a greater
abundance of
Diadema antillarum Philippi
closer to shore. Steneck (1994) reported
Diadema
populations of 16 individuals per square metre at
a depth of 3 m in Jamaica, compared with 2 indi-
viduals/m
2
and <1 individual/m
2
at depths of 10 m
and 20 m, respectively. Kiene & Hutchings (1994)
measured grazing rates of 0.30-1.96 kg m
2
yr
1
in shallow to mid-range depths off Lizard Island,
Australia compared with only 0.08-0.29 kg m
2
yr
1
in deeper water on the forereef; a similar but
variable trend was reported for total bioerosion.
Off Bonaire, Steneck & McClanahan (2004) mea-
sured a 75% decrease in bite density and size on
naturally occurring fl ora between shallow water
and 30 m depth.
Data for infaunal boring are less clear but, on
balance, infer a depth-related decrease in sub-
strate destruction. By inference, the increased
bioerosion by sponges within the wave-cut
notches of Bermuda (Neumann, 1966) argues for
greater sponge density close to sea level. Kiene &
Hutchings (1994) measured higher rates of boring
in shallower water, but the differences were not
statistically signifi cant. This is supported by data
from Moore & Shedd (1977), who reported a con-
sistent, depth-related decrease in sponge boring
on three Jamaican reefs (8-80% decrease between
15 m and 27 m; 65% decrease between 27 m and
40 m). Vogel
et al
. (2000) reported a consistent
decrease in microboring off Lee Stocking
Island (Bahamas), from 0.2 kg m
2
yr
1
at 2 m to
0.1 kg m
2
yr
1
at 10 m and 0.01 kg m
2
yr at 30 m.
Highsmith (1980) proposed that the abundance
of boring bivalves is proportional to primary pro-
ductivity, which should be higher in shallow
water where light intensity is greater. By con-
trast, Macdonald & Perry (2003) noted an increase
in bioerosion with depth within the lagoon of
Discovery Bay, Jamaica (8-10% loss shallower
than 16 m; 18% below 16 m). However, they also
noted heavy nutrient inputs from surrounding
development that, in this restricted environment,
could exert a control that overwhelms depth-
related patterns. Goreau & Hartman (1963) cited a
higher density of sponge boring at depths of 30 m
0
Bioerosion
export
10
20
Import
30
(m kyr
−
1
)
0
5
0
3
6
Reef accretion (kg m
−
2
yr
−
1
)
Fig. 11.
Stylized model explaining depth-related
differences between expected reef accretion based on
prevailing models and the results of this study. The lower
portion of the 'expected accretion' curve (
d
> 10 m) is based
on the measured growth rates and species mix at Cane Bay
Virgin Islands) and an assumed total-coral abundance of
approximately 50%. Accretion rates in water shallower
than 10 m were increased to allow for the greater accre-
tion assumed to be associated with branching
Acropora
palmata
. In this scenario, bioerosion decreases from a
maximum rate of
c
. 2.5 kg m
2
yr
1
in shallow water to
0.7 kg m
2
yr
1
at a depth of 25 m, based on data from the
literature cited in this paper. The remainder of the offset-
ting difference is related to sediment that is transported
downslope but stays within the reef.
or more, but this was in very slow-growing plate
corals. No actual bioerosion rates were reported,
and this may have refl ected low calcifi cation rates
rather than high infaunal excavation.
Figure 11 compares the depth-related trend in
accretion from this study to a stylized carbon-
ate-production curve based in part on data from
Cane Bay in the US Virgin Islands (Hubbard
et al
., 1990). In this scenario, increased bioerosion
in shallow water (2.0-2.5 kg m
2
yr
1
) offsets higher
calcifi cation rates. With increasing depth, both
calcifi cation and bioerosion decrease on parallel
tracks, resulting in the loss of a strong depth-
related change in reef accretion. It must be kept
in mind that bioerosion by itself cannot create the
depicted result. Accretion will be affected only
to the extent that the sediments produced by bio-
erosion are exported down the reef front. In this
scenario, the apparent homogenization of depth-
related accretion patterns also refl ects material
produced in shallow water being shifted into
deeper environs but remaining within the reef.
This exercise makes a signifi cant assumption
in creating a stylized production curve from
a single location and utilizing depth-related
