388
S. Gobert, M. L. Cambridge, B. Velimirov, et al.
turnover compared to the other seagrass (Duarte,
1991; Marb` a and Duarte, 1998; Marb` a and Walker,
1999; Hemminga and Duarte, 2000). Kuo and den
Hartog (2001) provide a good overview of all Posidonia species; see also, Kuo and den Hartog, Chapter
3 and Mateo et al., Chapter 7.
According to a review of the literature on seagrass
ecology (Duarte, 1999), about 600 papers have been
published in this area between 1989 and 1997. One
of every four papers on the biology and ecology of
all seagrass species was devoted to P. oceanica. Thus
Mediterranean beds have been studied more extensively than those of the Australian species of the
genus. The number of international papers on Posidonia spp. is rapidly increasing, but there is still a
paucity of papers devoted to the comparison of the
two different biogeographic regions.
This chapter describes Posidonia species and
ecosystem dynamics in relation to key ecological
processes and functions. We illustrate similarities
and differences between Mediterranean and Australian Posidonia ecosystems.
II. Systematics
On the basis of ecological, vegetative, and reproductive characteristics, nine seagrasses have been classified in the genus Posidonia (Den Hartog, 1970).
Eight species occur in Australian coastal waters
(P. angustifolia, P. australis, P. coriacea, P. denhartogii, P. kirkmanii, P. ostenfeldii, P. robertsoniae, and
P. sinuosa) (Cambridge and Kuo, 1979; Kuo and
Cambridge, 1984). One species, P. oceanica, is endemic to the Mediterranean Sea (Den Hartog, 1970;
Phillips and Me˜ nez, 1988).
Recent morphological and preliminary genetic
studies (Campey et al., 2000) emphasized the considerable overlap in vegetative characters (leaf widths,
epidermal cell dimensions, sheath lengths) used by
Kuo and Cambridge (1984) to distinguish species
of the Posidonia ostenfeldii group at sites in southwestern Australia and the need for further research
to resolve species boundaries. There is also need for
further investigation of the use of microsatellites to
determine the degree of difference that may exist in
P. oceanica.
III. Distribution of the Genus
The disjunct distribution of Posidonia is striking
(Fig. 1). P. oceanica is restricted to the Mediterranean Sea, whereas the other eight species of Posidonia occur across southern Australia (Short et al.,
2001; den Hartog and Kuo, Chapter 1). Genetically,
Mediterranean and Australian species of Posidonia are not close. The divergence in their DNA sequences (Waycott and Les, 2000) indicates that the
separation of the two groups took place at a relatively
early time in the history of the seagrasses, probably
during the Late Eocene. The origins of the genus are
postulated to have been in the Tethys Sea, but reconstructions of the position of shallow seas at that
time are not convincing as potential seagrass habitat
(Hemminga and Duarte, 2000).
The beds in the Mediterranean Sea (Fig. 1) cover a
surface area of 25,000–50,000 km
2 representing 1–
2% of the total surface (Pasqualini et al., 1998). The
western distributional limit of P. oceanica is associated with the Almeria–Oran density front (boundary between water masses of different density which
separates the Atlantic from the Mediterranean surface waters; 250 km eastward from Gibraltar strait)
(Marb` a et al., 1996). The eastern distribution limit
is more eastwards in the Northern coast than in
African coast. Beds are less widespread in the eastern basin and are not recorded along the coasts of
Lebanon, Israel, and Syria. In terms of depth limits,
P. oceanica meadows are recorded from 0.5 to 40 m
(Boudouresque and Meinesz, 1982; Pergent et al.,
1995), and living plants have been found at 48 m
depth (Augier and Boudouresque, 1979). In turbid
waters, the lower limit of the beds is of the order
of 9 m (Pergent et al., 1995). In many inshore areas
of the Mediterranean, P. oceanica is widespread but
disappears near river mouths where the input of fresh
water and fine sediments is high (Rhˆ one, Po, Nile).
Along Australian coasts, the genus Posidonia is
widely distributed, from 23
◦ S on the west coast to
32
◦ S on the east coast (Larkum and den Hartog,
1989), a distance of more than 4,000 km (Fig. 1).
With the exception of P. australis, Australian species
of Posidonia occur on the temperate west and south
coasts, a region characterized by microtides (<1 m),
clear, warm temperate waters, an arid hinterland with
low run-off and coastal geomorphology dominated
by Pleistocene sediments (Kirkman and Walker,
1989; Walker, 2000). They occur at depths ranging
from the intertidal to more than 35 m (Cambridge
and Kuo, 1979; Kuo and Cambridge, 1984) with the
deepest record of 44 m for P. angustifolia (Huisman
et al., 1999), in sedimentary environments varying in wave exposure from sheltered embayments
(e.g. Shark Bay, Cockburn Sound, Frenchmans Bay,
S. Gobert, M. L. Cambridge, B. Velimirov, et al.
turnover compared to the other seagrass (Duarte,
1991; Marb` a and Duarte, 1998; Marb` a and Walker,
1999; Hemminga and Duarte, 2000). Kuo and den
Hartog (2001) provide a good overview of all Posidonia species; see also, Kuo and den Hartog, Chapter
3 and Mateo et al., Chapter 7.
According to a review of the literature on seagrass
ecology (Duarte, 1999), about 600 papers have been
published in this area between 1989 and 1997. One
of every four papers on the biology and ecology of
all seagrass species was devoted to P. oceanica. Thus
Mediterranean beds have been studied more extensively than those of the Australian species of the
genus. The number of international papers on Posidonia spp. is rapidly increasing, but there is still a
paucity of papers devoted to the comparison of the
two different biogeographic regions.
This chapter describes Posidonia species and
ecosystem dynamics in relation to key ecological
processes and functions. We illustrate similarities
and differences between Mediterranean and Australian Posidonia ecosystems.
II. Systematics
On the basis of ecological, vegetative, and reproductive characteristics, nine seagrasses have been classified in the genus Posidonia (Den Hartog, 1970).
Eight species occur in Australian coastal waters
(P. angustifolia, P. australis, P. coriacea, P. denhartogii, P. kirkmanii, P. ostenfeldii, P. robertsoniae, and
P. sinuosa) (Cambridge and Kuo, 1979; Kuo and
Cambridge, 1984). One species, P. oceanica, is endemic to the Mediterranean Sea (Den Hartog, 1970;
Phillips and Me˜ nez, 1988).
Recent morphological and preliminary genetic
studies (Campey et al., 2000) emphasized the considerable overlap in vegetative characters (leaf widths,
epidermal cell dimensions, sheath lengths) used by
Kuo and Cambridge (1984) to distinguish species
of the Posidonia ostenfeldii group at sites in southwestern Australia and the need for further research
to resolve species boundaries. There is also need for
further investigation of the use of microsatellites to
determine the degree of difference that may exist in
P. oceanica.
III. Distribution of the Genus
The disjunct distribution of Posidonia is striking
(Fig. 1). P. oceanica is restricted to the Mediterranean Sea, whereas the other eight species of Posidonia occur across southern Australia (Short et al.,
2001; den Hartog and Kuo, Chapter 1). Genetically,
Mediterranean and Australian species of Posidonia are not close. The divergence in their DNA sequences (Waycott and Les, 2000) indicates that the
separation of the two groups took place at a relatively
early time in the history of the seagrasses, probably
during the Late Eocene. The origins of the genus are
postulated to have been in the Tethys Sea, but reconstructions of the position of shallow seas at that
time are not convincing as potential seagrass habitat
(Hemminga and Duarte, 2000).
The beds in the Mediterranean Sea (Fig. 1) cover a
surface area of 25,000–50,000 km
2 representing 1–
2% of the total surface (Pasqualini et al., 1998). The
western distributional limit of P. oceanica is associated with the Almeria–Oran density front (boundary between water masses of different density which
separates the Atlantic from the Mediterranean surface waters; 250 km eastward from Gibraltar strait)
(Marb` a et al., 1996). The eastern distribution limit
is more eastwards in the Northern coast than in
African coast. Beds are less widespread in the eastern basin and are not recorded along the coasts of
Lebanon, Israel, and Syria. In terms of depth limits,
P. oceanica meadows are recorded from 0.5 to 40 m
(Boudouresque and Meinesz, 1982; Pergent et al.,
1995), and living plants have been found at 48 m
depth (Augier and Boudouresque, 1979). In turbid
waters, the lower limit of the beds is of the order
of 9 m (Pergent et al., 1995). In many inshore areas
of the Mediterranean, P. oceanica is widespread but
disappears near river mouths where the input of fresh
water and fine sediments is high (Rhˆ one, Po, Nile).
Along Australian coasts, the genus Posidonia is
widely distributed, from 23
◦ S on the west coast to
32
◦ S on the east coast (Larkum and den Hartog,
1989), a distance of more than 4,000 km (Fig. 1).
With the exception of P. australis, Australian species
of Posidonia occur on the temperate west and south
coasts, a region characterized by microtides (<1 m),
clear, warm temperate waters, an arid hinterland with
low run-off and coastal geomorphology dominated
by Pleistocene sediments (Kirkman and Walker,
1989; Walker, 2000). They occur at depths ranging
from the intertidal to more than 35 m (Cambridge
and Kuo, 1979; Kuo and Cambridge, 1984) with the
deepest record of 44 m for P. angustifolia (Huisman
et al., 1999), in sedimentary environments varying in wave exposure from sheltered embayments
(e.g. Shark Bay, Cockburn Sound, Frenchmans Bay,