Geology Reference
In-Depth Information
coast of Eyre Peninsula, and the Bonney Shelf
(Schahinger, 1987; Griffi n
et al
., 1997; Middleton &
Platov, 2003).
Spencer Gulf and Gulf St. Vincent (including
Investigator Strait) are inverse estuaries (NunesVaz
et al
., 1990), where seawater is concentrated by
evaporation exceeding precipitation. Salinities at
the head of Spencer Gulf remain above 40‰ year-
round while water temperatures fall to ~12°C in
the winter and rise to 24°C in summer (Bye, 1983).
Temperature and salinity gradients in Gulf
St. Vincent are not as strong as those in Spencer
Gulf. Although the River Murray (Fig. 2) is the
largest river in Australia its mouth is generally
sealed by longshore drift and so it has little infl u-
ence on Lacepede Shelf waters, which are normal
marine throughout.
is attached to the living outer tissues of the plant:
it is assumed that it does not derive food or
nutrients from the host'.
Previous studies
The fi rst studies evaluating the quantity of car-
bonate from epiphytes were carried out by Land
(1970), Patriquin (1972) and Smith (1972). Nelsen &
Ginsburg (1986) concluded that the epibionts
(epiphytes) could account for the entire high-
magnesium calcite (HMC) and aragonite mud-
sized fraction within eastern Florida Bay. There
are only three other sedimentological studies of
epiphyte carbonate productivity in tropical waters
(Boscence, 1989; Frankovich & Zieman, 1994;
Corlett & Jones, 2007) and one in the subtropical
realm (Perry & Beavington-Penney, 2005).
In South Australia there has been only one
examination of seagrass calcareous epiphytes and
this is only at one site (Thomas & Clarke, 2001). In
contrast, there are numerous studies in Western
Australia (Smith & Atkinson, 1983; Searle, 1984;
Horner, 1987; Walker & Woerkerling, 1988; Walker
et al
., 1991; Sim, 1991; Lord, 1998; Lavery &
Vanderklift, 2000).
Sedimentology
The seafl oor throughout the area is covered by
heterozoan carbonate sediment (cf. James, 1997).
The carbonate fraction of the deposits is almost
wholly biogenic and produced mainly by coral-
line algae, foraminifera, molluscs, bryozoans and
echinoderms (Gostin
et al
., 1988; James
et al
.,
1992, 1997, 2001; Fuller
et al
., 1994). In some
inboard areas they are augmented by tests of large
symbiont-bearing foraminifera (particularly
Peneroplis
sp.) and locally in the gulfs there
is sporadic growth of the zooxanthellate coral
Pleiseastrea
sp. Thus, overall the sedimentary
environment is at the warmer end of the cool-
water spectrum (cf. Betzler
et al
., 1997).
METHODS
Site selection
Twenty study sites were chosen to represent
the wide variety of settings in which seagrass
is found (Fig. 4). They ranged from the head of
reverse estuaries (Gulf St. Vincent and Spencer
Gulf) to environments exposed to the Southern
Ocean. Water depths ranged from 0.4 to 15.5 m
w.d., across a salinity range of 32.2-43.7‰ with
surface-water temperatures varying from 14.1 to
25.8°C. West Island was chosen for detailed study
because it faced the Southern Ocean and because
there was a marine laboratory on the island that
facilitated diving and analysis. Chinaman Creek
was selected for additional study because it repre-
sented the other extreme, a restricted, seasonally
saline and high-temperature environment.
TERMINOLOGY, PREVIOUS STUDIES
Terminology
The following groups of calcareous organisms
are known to grow on seagrasses; coralline algae,
bryozoans, foraminifera, serpulids, spirorbids,
ostracods and bivalves (Humm, 1964; Ducker
et al
., 1977; Ducker & Knox, 1978; Harlin,
1980). The name for organisms growing on a
variety of marine hosts is the subject of an
extensive literature (Harlin, 1980; Borowitzka &
Lethbridge, 1989; Taylor, 1990; Frankovich &
Zeiman, 1994; Hageman
et al
., 1996; Womersley,
1996; Jernakoff
et al
., 1996; English
et al
., 1997).
The term calcareous epiphyte is herein defi ned
as 'an organism, plant or animal, that secretes a
calcareous skeleton and that, for most of its life
Sample collection
Marine study was undertaken by snorkeling
or SCUBA diving where appropriate. Each site
was visited at least once. West Island (Fig. 4)
was studied in detail at one shallow-water site
