Geology Reference
In-Depth Information
138
°
134
°
136
°
140
°
142
°
HEAD OF BIGHT
E
ucla
GREAT
AUSTRALIAN
BIGHT
Ceduna
SOUTH AUSTRALIA
AUSTRALIA
Streaky
Bay
100
E
lliston
LEEUWIN
CURRENT
EYRE
PENINSULA
N.S.W.
Spencer
Gulf
Port
Lincoln
N
ADELAIDE
Victor
Harbor
5000
Inv
KANGAROO
ISLAND
LACEPEDE
SHELF
MAJOR CURRENTS
Kingston
Mount
Gambier
CONTOURS IN METRES
Port
Macdonnell
0
100
200
300
BONNEY
SHELF
Po
rtland
kilometres
138
°
142
°
134
°
136
°
140
°
Fig. 2.
Chart of the central part of southern Australia and location of the study area, main ocean circulation patterns, areas
of upwelling and location of major population centres.
seagrass are known in South Australian coastal
waters (Edyvane, 1999b).
Seagrasses present off South Australia are
mainly from the genera
Posidonia, Amphibolis,
Heterozostera, Zostera
and
Halophila
, of which
only the fi rst two are signifi cant as hosts for cal-
careous epiphytes. Three species of
Posidonia
(
P. sinuosa, P. angustifolia
, and
P. australis
) and
two species of
Amphibolis
(
A. antarctica
and
A. griffi thii
) were studied. The shelf off South
Australia, the region of this study, is, however, near
the southern limit of their range (Robertson, 1984,
1986; Shepherd & Robertson, 1989; Kirkman, 1997;
Edgar, 2000, 2001).
Posidonia
sp. and
Amphibolis
sp.
species generally decline in abundance to the
east. This has been attributed to their affi nity
with warm temperate waters that decrease to the
east with the reduced effects of the warm water
Leeuwin Current (Kirkman, 1997).
These marine angiosperms consist of a well-
developed rhizome that runs in sediment beneath
the seabed and has regularly spaced nodes, each
bearing roots below and an erect stem or shoot with
strap-like leaves above. The structure of these two
grasses is somewhat different. Whereas
Posidonia
has a shoot with blades growing upward from
close to the sediment-water interface,
Amphibolis
has a relatively long stem extending well above
the sediment from which clusters of blades emerge
(Fig. 3). Both have strong root systems that form
a dense mat within the sediment and both shed
their leaves over a period of about 2 months.
Posidonia
Posidonia australis
is found in sheltered sand
and mud environments, in 0-15 m water depth
(m w.d.), from Shark Bay in Western Australia
across southern Australia to Lake Macquarie on
the east coast and along the northern coast of
Tasmania. The maximum leaf length is 450 mm
and maximum width is 20 mm. Rhizomes lie hori-
zontally at a depth of 10-20 cm below the sediment
surface. This, the most widely dispersed form
