394
S. Gobert, M. L. Cambridge, B. Velimirov, et al.
(Marb` a and Walker, 1999; Campey et al., 2002) or
by temperature. Flowering occurs more frequently in
shallow sites than deeper ones (Pergent and PergentMartini, 1988; Cambridge and Hocking, 1997). Production of reproductive shoots is an episodic phenomenon in some areas (i.e. central New South
Wales, Northwestern Mediterranean) but a regular
annual event on the western and southern coasts of
Australia. Flowering of P. oceanica occurred over
the entire Mediterranean basin, in 1961, 1967, 1971,
1972, 1973, 1975, 1979, 1981, 1982, and 1983
(Pergent and Pergent-Martini, 1990) and in 1994
(Sandmeier et al., 1999).
Flower buds emerge in Posidonia species during April–June. Anthesis begins in July continuing
through to September (late winter and late summer
in Australia and Mediterranean Sea, respectively),
followed by fruit and seed development, with fruits
being shed from November to January, depending
on the species (Hocking et al., 1981, Cambridge
and Hocking, 1997; Gobert et al., 2001; Smith and
Walker, 2002). Flowering requires additional nutrients (Cambridge and Hocking, 1997; Gobert et al.,
2005) and can affect the biometry of the flowerbearing shoot (Gobert et al., 2001). The fruits contain nutrient reserves—i.e. an accumulation of N, P,
K, Ca, Mg, Na, Fe, Zn, Mn, and Cu in the developing pericarp of P. australis and P. sinuosa (Hocking et al., 1980). P. oceanica produces fewer flowers
than other Posidonia species (i.e. mean flowering ratio: <1% for P. oceanica; 20% for P. australis; 3%
for P. sinuosa; 8% for P. coriacea) (Pergent et al.,
1997a).
In the Mediterranean, P. oceanica flowers rarely in
the cold waters along north-western shores, whereas
flowering is frequent or even annual in the southern and eastern regions of the Mediterranean basin
(Molinier and Picard, 1952). Flowers and fruits of
P. oceanica have been observed at many localities
within the Mediterranean basin (Den Hartog, 1970;
Giraud, 1977b; Mazzella et al., 1983; Pergent, 1985;
Buia and Mazzella, 1991; Gobert et al., 2001). The
establishment of seedlings is episodic. Germination
begins with the development of the plumule following by the protusion of a white primary root at
the radical pole, all occurring within the pericarp.
There is no seed bank in Posidonia. After about 10
days, the apical meristem grows and produces 2 or
3 green leaves and several adventitious white roots.
After 9 months, seedlings have 12–13 leaves, one
primordial tap-root and 3–4 adventitious roots. At
this stage, a high of mortality occurred (Balestri and
Cinelli, 1995). P. oceanica seedlings begin to develop their own rhizome, growing horizontally at a
rate of about 5–10 cm year
−1 (Boudouresque and
Meinesz, 1982). Grazing of inflorescences can affect the success of sexual reproduction (Piazzi et al.,
2000).
In southeastern Australia, P. australis flowers infrequently (West and Larkum, 1979), associated
with changes in water temperature (i.e. monthly
mean temperatures 1–2
◦ C cooler than in the previous 7 years) (Inglis and Lincoln-Smith, 1998).
In contrast, P. australis flowers frequently in Western Australia and produces large numbers of seeds
(Cambridge and Hocking, 1997; Marb` a and Walker,
1996). Posidonia seeds deposited on unvegetated
sand suffer a lower predation pressure (Orth et al.,
2002). Seeds seem to play an important role in initial establishment, playing a lesser role in subsequent meadow development and maintenance in the
short term compared to vigorous clonal growth. Kuo
and Kirkman (1996) estimated that about 2% of
seedlings survived beyond 1 year in trial plots at a site
near Perth using three species of Posidonia. Genetic
studies on P. australis showed populations consisting of multiclonal beds with a high degree of genetic
variation, demonstrating the success of seedling establishment over longer time scales (Waycott, 1995;
Waycott and Sampson, 1997).
The flowering phenology characteristics (flower
structure, flower location on plant, vegetation canopy
structure, longevity of flowering, pollen viability)
differ from one species to another (Cambridge and
Kuo, 1979; Smith and Walker, 2002). These differences may be related to different pollination strategies, e.g. low pollen dispersal, enclosed in a dense
canopy, that probably induce greater neighbor–
neighbor pollination for P. sinuosa or large pollen,
dispersal above the canopy for P. australis (Smith
and Walker, 2002).
B. Genetic Consequences
There are contrasts in the findings of the limited genetic studies of the genus Posidonia. For example,
there is a high degree of genetic diversity within
populations of the Australian P. australis (Waycott
et al., 1997) but less genetic diversity in P. sinuosa (Wood et al., 1999). The genetic diversity of
P. oceanica is very low. P. oceanica occurs in separate meadows that represent discrete populations
with limited inbreeding (Procaccini and Mazzella,
S. Gobert, M. L. Cambridge, B. Velimirov, et al.
(Marb` a and Walker, 1999; Campey et al., 2002) or
by temperature. Flowering occurs more frequently in
shallow sites than deeper ones (Pergent and PergentMartini, 1988; Cambridge and Hocking, 1997). Production of reproductive shoots is an episodic phenomenon in some areas (i.e. central New South
Wales, Northwestern Mediterranean) but a regular
annual event on the western and southern coasts of
Australia. Flowering of P. oceanica occurred over
the entire Mediterranean basin, in 1961, 1967, 1971,
1972, 1973, 1975, 1979, 1981, 1982, and 1983
(Pergent and Pergent-Martini, 1990) and in 1994
(Sandmeier et al., 1999).
Flower buds emerge in Posidonia species during April–June. Anthesis begins in July continuing
through to September (late winter and late summer
in Australia and Mediterranean Sea, respectively),
followed by fruit and seed development, with fruits
being shed from November to January, depending
on the species (Hocking et al., 1981, Cambridge
and Hocking, 1997; Gobert et al., 2001; Smith and
Walker, 2002). Flowering requires additional nutrients (Cambridge and Hocking, 1997; Gobert et al.,
2005) and can affect the biometry of the flowerbearing shoot (Gobert et al., 2001). The fruits contain nutrient reserves—i.e. an accumulation of N, P,
K, Ca, Mg, Na, Fe, Zn, Mn, and Cu in the developing pericarp of P. australis and P. sinuosa (Hocking et al., 1980). P. oceanica produces fewer flowers
than other Posidonia species (i.e. mean flowering ratio: <1% for P. oceanica; 20% for P. australis; 3%
for P. sinuosa; 8% for P. coriacea) (Pergent et al.,
1997a).
In the Mediterranean, P. oceanica flowers rarely in
the cold waters along north-western shores, whereas
flowering is frequent or even annual in the southern and eastern regions of the Mediterranean basin
(Molinier and Picard, 1952). Flowers and fruits of
P. oceanica have been observed at many localities
within the Mediterranean basin (Den Hartog, 1970;
Giraud, 1977b; Mazzella et al., 1983; Pergent, 1985;
Buia and Mazzella, 1991; Gobert et al., 2001). The
establishment of seedlings is episodic. Germination
begins with the development of the plumule following by the protusion of a white primary root at
the radical pole, all occurring within the pericarp.
There is no seed bank in Posidonia. After about 10
days, the apical meristem grows and produces 2 or
3 green leaves and several adventitious white roots.
After 9 months, seedlings have 12–13 leaves, one
primordial tap-root and 3–4 adventitious roots. At
this stage, a high of mortality occurred (Balestri and
Cinelli, 1995). P. oceanica seedlings begin to develop their own rhizome, growing horizontally at a
rate of about 5–10 cm year
−1 (Boudouresque and
Meinesz, 1982). Grazing of inflorescences can affect the success of sexual reproduction (Piazzi et al.,
2000).
In southeastern Australia, P. australis flowers infrequently (West and Larkum, 1979), associated
with changes in water temperature (i.e. monthly
mean temperatures 1–2
◦ C cooler than in the previous 7 years) (Inglis and Lincoln-Smith, 1998).
In contrast, P. australis flowers frequently in Western Australia and produces large numbers of seeds
(Cambridge and Hocking, 1997; Marb` a and Walker,
1996). Posidonia seeds deposited on unvegetated
sand suffer a lower predation pressure (Orth et al.,
2002). Seeds seem to play an important role in initial establishment, playing a lesser role in subsequent meadow development and maintenance in the
short term compared to vigorous clonal growth. Kuo
and Kirkman (1996) estimated that about 2% of
seedlings survived beyond 1 year in trial plots at a site
near Perth using three species of Posidonia. Genetic
studies on P. australis showed populations consisting of multiclonal beds with a high degree of genetic
variation, demonstrating the success of seedling establishment over longer time scales (Waycott, 1995;
Waycott and Sampson, 1997).
The flowering phenology characteristics (flower
structure, flower location on plant, vegetation canopy
structure, longevity of flowering, pollen viability)
differ from one species to another (Cambridge and
Kuo, 1979; Smith and Walker, 2002). These differences may be related to different pollination strategies, e.g. low pollen dispersal, enclosed in a dense
canopy, that probably induce greater neighbor–
neighbor pollination for P. sinuosa or large pollen,
dispersal above the canopy for P. australis (Smith
and Walker, 2002).
B. Genetic Consequences
There are contrasts in the findings of the limited genetic studies of the genus Posidonia. For example,
there is a high degree of genetic diversity within
populations of the Australian P. australis (Waycott
et al., 1997) but less genetic diversity in P. sinuosa (Wood et al., 1999). The genetic diversity of
P. oceanica is very low. P. oceanica occurs in separate meadows that represent discrete populations
with limited inbreeding (Procaccini and Mazzella,