Chapter 17 Biology of Posidonia
395
1998; Procaccini et al., 2001). The low genetic polymorphism of Posidonia could be a disadvantage in
facing anthropogenic pressure with potential effects
on survival and expansion (Procaccini and Piazzi,
2001).
C. Recruitment
The contribution of the sexual reproduction to the
maintenance and to expansion of Posidonia beds
varies greatly between species. Sexual reproduction
contributes to recruitment (Procaccini and Mazzella,
1998; Campey et al., 2002) but vegetative reproduction often maintains the meadows (Buia and
Mazzella, 1991; Procaccini and Mazzella, 1998;
Kirkman and Kuo, 1990; Duarte et al., Chapter
11). Recruitment of seedlings appears important for
the persistence and the expansion of P. coriacea
(Kendrick et al., 1999). Sexual reproduction varies
in time as does the probability that flowers set fruits,
seeds (P. coriacea: 21% (Campey et al., 2002); P.
australis: 23–37% (Waycott et al., 1997); P. oceanica: 2%, (Balestri and Cinelli, 2003)) and finally develop new shoots. Variations in the number of flowers per inflorescence, in the number of fruits per
inflorescence (Cambridge and Hocking, 1997) and
in the fate of successful seeds, for example due to
predation (Piazzi et al., 2000; Orth et al., 2002), are
all variable. A discussion of recruitment strategies
in Posidonia species and other genera is given by
Orth et al. (Chapter 5).
VII. Dynamics of Carbon and Nitrogen
The Posidonia bed, as an important primary producer, is also a recognized sink for biogenic elements
(Romero et al., 1992; Mat` eo et al., 1997; see also
Mateo et al., Chapters 7 and Romero et al., Chapter 9,
this volume) and could act as a sink for atmospheric
CO 2 (Frankignoulle and Bouquegneau, 1987). The
beds play a major role in the production (Logan et
al., 1970; Walker and Woelkerling, 1988) trapping
(De Falco et al., 2000) and stabilization of sediments
(Boudouresque and Meinesz, 1982).
The accumulation rate of sedimentary matter in a
P. oceanica bed (Calvi Bay–Corsica) varied over the
year (average: 0.33 g dw m
−2 day
−1 ) (Dauby, 1989).
The total matter flux over a yearly cycle is about
1.3 kg m
−2 , which corresponds to a mean daily flux
of 3.7 g m
−2 . This amount of material consists of
water column-originated and resuspended particles.
The relative importance of each fraction changes
several times during the year with respect to climatic
or biological events. The measured yearly flux of settling suspended particulate matter was about 420 g
m
−2 , which corresponds to a mean daily flux of 1.2 g
m
−2 . In absence of resuspension, the canopy slightly
increased particle trapping (Gacia et al., 1999); only
about 10% of the matter produced in the pelagic zone
sinks and reaches the bottom, probably as a result of
the high grazing pressure suffered by phytoplankton in such waters (Dauby, 1989). The litter is partly
exported and partly slowly degraded, but a fraction
remains in the upper sediment layer and is thus easily
remobilized (Dauby et al., 1995).
A. Carbon
Seagrasses are important contributors to oceanic net
carbon production (Duarte and Cebri´ an, 1996): exceeding 15 gC m
−2 day
−1 in some areas (Phillips
and McRoy, 1980). This organic carbon produced is
important in the environment and in the food chain
(i.e. Nichols et al., 1986).
Carbon metabolism has been described for seagrasses in general (Touchette and Burkholder,
2000b; Larkum et al., Chapter 14), for Australian
Posidonia (i.e. Abel and Drew, 1989; James and
Larkum, 1996) and for P. oceanica (e.g. Alcoverro
et al., 1998, 2001a,b; Modigh et al., 1998; Mateo et
al., Chapter 7). Carbon dynamics vary considerably
between species, location and season.
In an eastern Australian estuary, in P. australis
beds, 37% of the year’s production sank to the bottom
and was utilized by benthic detritivores, 12% was
exported as floating leaves and only 3% of the production was eaten by herbivores (Kirkman and Reid,
1979). Occasionaly, accumulations of persistent organic matter may develop in sediments (Hemminga
and Duarte, 2000). In Shark Bay, rates of decomposition of P. australis were 0.5% day
−1 (Walker and
McComb, 1985).
In the Mediterranean Sea, P. oceanica leaves contain 23–40% of carbon, varying with depth, season and leaf age (Augier and Santimone, 1982;
Velimirov, 1987; Duarte, 1990; Alcoverro et al.,
1995; Gobert et al., 1995; Mateo et al., Chapter
7). Seasonal and daily variations of soluble carbohydrates, starch, and free amino acids were investigated in detail by Velimirov (1984); Pirc and
Wollenweber (1988); Alcoverro et al. (2001b). The
carbon fluxes of the beds, resulting essentially from
P. oceanica primary production, vary according to
395
1998; Procaccini et al., 2001). The low genetic polymorphism of Posidonia could be a disadvantage in
facing anthropogenic pressure with potential effects
on survival and expansion (Procaccini and Piazzi,
2001).
C. Recruitment
The contribution of the sexual reproduction to the
maintenance and to expansion of Posidonia beds
varies greatly between species. Sexual reproduction
contributes to recruitment (Procaccini and Mazzella,
1998; Campey et al., 2002) but vegetative reproduction often maintains the meadows (Buia and
Mazzella, 1991; Procaccini and Mazzella, 1998;
Kirkman and Kuo, 1990; Duarte et al., Chapter
11). Recruitment of seedlings appears important for
the persistence and the expansion of P. coriacea
(Kendrick et al., 1999). Sexual reproduction varies
in time as does the probability that flowers set fruits,
seeds (P. coriacea: 21% (Campey et al., 2002); P.
australis: 23–37% (Waycott et al., 1997); P. oceanica: 2%, (Balestri and Cinelli, 2003)) and finally develop new shoots. Variations in the number of flowers per inflorescence, in the number of fruits per
inflorescence (Cambridge and Hocking, 1997) and
in the fate of successful seeds, for example due to
predation (Piazzi et al., 2000; Orth et al., 2002), are
all variable. A discussion of recruitment strategies
in Posidonia species and other genera is given by
Orth et al. (Chapter 5).
VII. Dynamics of Carbon and Nitrogen
The Posidonia bed, as an important primary producer, is also a recognized sink for biogenic elements
(Romero et al., 1992; Mat` eo et al., 1997; see also
Mateo et al., Chapters 7 and Romero et al., Chapter 9,
this volume) and could act as a sink for atmospheric
CO 2 (Frankignoulle and Bouquegneau, 1987). The
beds play a major role in the production (Logan et
al., 1970; Walker and Woelkerling, 1988) trapping
(De Falco et al., 2000) and stabilization of sediments
(Boudouresque and Meinesz, 1982).
The accumulation rate of sedimentary matter in a
P. oceanica bed (Calvi Bay–Corsica) varied over the
year (average: 0.33 g dw m
−2 day
−1 ) (Dauby, 1989).
The total matter flux over a yearly cycle is about
1.3 kg m
−2 , which corresponds to a mean daily flux
of 3.7 g m
−2 . This amount of material consists of
water column-originated and resuspended particles.
The relative importance of each fraction changes
several times during the year with respect to climatic
or biological events. The measured yearly flux of settling suspended particulate matter was about 420 g
m
−2 , which corresponds to a mean daily flux of 1.2 g
m
−2 . In absence of resuspension, the canopy slightly
increased particle trapping (Gacia et al., 1999); only
about 10% of the matter produced in the pelagic zone
sinks and reaches the bottom, probably as a result of
the high grazing pressure suffered by phytoplankton in such waters (Dauby, 1989). The litter is partly
exported and partly slowly degraded, but a fraction
remains in the upper sediment layer and is thus easily
remobilized (Dauby et al., 1995).
A. Carbon
Seagrasses are important contributors to oceanic net
carbon production (Duarte and Cebri´ an, 1996): exceeding 15 gC m
−2 day
−1 in some areas (Phillips
and McRoy, 1980). This organic carbon produced is
important in the environment and in the food chain
(i.e. Nichols et al., 1986).
Carbon metabolism has been described for seagrasses in general (Touchette and Burkholder,
2000b; Larkum et al., Chapter 14), for Australian
Posidonia (i.e. Abel and Drew, 1989; James and
Larkum, 1996) and for P. oceanica (e.g. Alcoverro
et al., 1998, 2001a,b; Modigh et al., 1998; Mateo et
al., Chapter 7). Carbon dynamics vary considerably
between species, location and season.
In an eastern Australian estuary, in P. australis
beds, 37% of the year’s production sank to the bottom
and was utilized by benthic detritivores, 12% was
exported as floating leaves and only 3% of the production was eaten by herbivores (Kirkman and Reid,
1979). Occasionaly, accumulations of persistent organic matter may develop in sediments (Hemminga
and Duarte, 2000). In Shark Bay, rates of decomposition of P. australis were 0.5% day
−1 (Walker and
McComb, 1985).
In the Mediterranean Sea, P. oceanica leaves contain 23–40% of carbon, varying with depth, season and leaf age (Augier and Santimone, 1982;
Velimirov, 1987; Duarte, 1990; Alcoverro et al.,
1995; Gobert et al., 1995; Mateo et al., Chapter
7). Seasonal and daily variations of soluble carbohydrates, starch, and free amino acids were investigated in detail by Velimirov (1984); Pirc and
Wollenweber (1988); Alcoverro et al. (2001b). The
carbon fluxes of the beds, resulting essentially from
P. oceanica primary production, vary according to