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grass beds are arguably the dominant nearshore
carbonate factory throughout this vast temperate
water realm.
Finally, the mixed Mg-calcite and aragonite
mineralogy further refl ects the source partition-
ing; Mg calcite (corallines, bryozoans, benthic
foraminifera) comes largely from the grasses
whereas, although some aragonite is produced by
annelids, most of the aragonite comes from infau-
nal bivalves and gastropods.
6
Abundances of coralline algae >> bryozoans =
foraminifera >> than all other calcareous epi-
phytes. Non-geniculate (encrusting) corallines
are more common on seagrasses than geniculate
(erect articulated) forms.
Calculated values of epiphyte production
7
26 g m
2
yr
1
or 750 g kg
1
of sea-
grass per year. The range is 49-661 g m
2
yr
1
.
These amounts are similar to those produced
in tropical environments where values aver-
age 118-281 g m
2
yr
1
. Calculated accumula-
tion rates of calcareous epiphyte carbonate
is ~7.4 cm kyr
1
.
The composition of sediment produced by most
average 210
Accumulation rates
Seagrass epiphytes in temperate environments
produce, as in tropical settings, a considerable
amount of carbonate sediment. Accumulation rates
of that portion of the sediment produced in grass-
beds, as measured by sediment cores of Quaternary
sediment (Burne & Colwell, 1982; Gostin
et al
.,
1984), ranges between 20 and 270 cm kyr
1
or
overall between 10 and 100 cm kyr
1
(James,
1997). This sediment comes not only from the
epiphytes on the grass but also from the infaunal
and epifauanal biota. This study indicates that a
large proportion of the sediment comes from the
epiphytes.
8
epiphytes (corallines, benthic foraminifera,
bryozoans) is mostly Mg calcite, with minor
aragonite produced by annelids.
ACKNOWLEDGEMENTS
This research was funded principally by the
Australian Research Council through a grant to YB
and AC and an Australian Postgraduate Research
Award to KMB as well as funds from a Natural
Sciences and Engineering Research Council
of Canada Discovery Grant to NPJ. Assistance
in identifying the epiphytes was provided by
M. Davies (ostracods), and Q. Li (benthic foramin-
ifera) and R. Schmidt (bryozoans). B. Jones and
D. Boscence kindly read and made helpful com-
ments on an early draft of this study while this
paper was improved by comments from J. Reijmer
and an anonymous reviewer.
CONCLUSIONS
1
The predominant control on the abundance of
calcareous epiphytes is seagrass biomass. Over
74% of the quadrats sampled during this study
had seagrass biomass values between 50 and
500 g m
2
. Seagrass biomass has a peak value at
24 m water depth.
Epiphytic carbonate abundance changes
2
REFERENCES
signifi cantly with water depth, increasing from
0 to 10 m water depth and then decreasing as
depth increases.
Each of the 20 sites examined had different
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and
Bourman, R.P.
(1997) Sea-level indicators from a Holocene, tide-
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Betzler, C., Brachert, T.C.
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Lethbridge, R.C.
(1989) Seagrass
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Species richness, spatial distribution and coloniza-
tioin pattern of algal and invertebrate epiphytes on the
3
abundances of calcareous epiphytes, thus gen-
eralizations are dangerous and diffi cult.
Greater abundance of epiphytes is associated
4
with
Amphibolis
compared with
Posidonia
because of the greater accumulation of cal-
careous epiphytes over time on the relatively
long-lived
Amphibolis
stems.
Amphibolis
is
more susceptible to epiphyte encrustation than
Posidonia
.
Decline in carbonate production during
5
autumn-winter is attributed to simultaneous
decrease in seagrass biomass, hence recruit-
ment space.
