Chapter 17 Biology of Posidonia
401
region supports agriculture and mariculture as well
as wild fisheries, industry, and navigation.
Monitoring strategies have been recently proposed to control and conserve meadow habitats (e.g.
Moreno et al., 2001). Seagrass meadows are a priority habitat under the European Union Species and
Habitats Directive (H&SD, 92/43/EEC).
The protection and conservation is of primary importance, but the replanting of Posidonia shoots is
slow and difficult. Survival of transplants is low in
the Mediterranean (Molenaar and Meinesz, 1995;
Molenaar et al., 2000), and only about 40% survive
in southern Australia (Lord et al., 1999). Transplantation is accompanied by modifications of biometry,
and modifications of C, N, and P content, which reflect weakness of the strategy (Lepoint et al., 2004a).
One year after transplanting, shoots are still unable to satisfy their nutrient demand (Gobert, 2004;
Lepoint et al., 2004; Vangeluwe et al., 2004).
The introduction of exotic marine organisms,
from accidental release, vessel ballast water, hull
fouling, and aquaculture, remains an area of concern
(Boudouresque and Verlaque, 2002; Duarte et al. in
press; Ralph et al. Chapter 24), particularly where the
introduced species are competitors for soft bottom
substratum such as the algae Caulerpa taxifolia, and
Caulerpa racemosa in the Mediterranean (Meinesz
et al., 1993; Deville and Verlaque, 1995; Ceccherelli
and Cinelli, 1999) and the fan worm Sabella spallanzanii in southern Australia (Lemmens et al., 1996).
Aquaculture of fish and algal biomass has been
shown to produce major environmental impacts, particularly due to shading, eutrophication, and sediment deterioration through excess organic inputs
(Seymour and Bergheim, 1991; Shireman and Cichra, 1994; Dosdat et al., 1995; Holmer et al., 2001).
The effects of fish farms and other aquaculture developments are of concern as areas of productive
seagrass habitats are often targeted for such developments, such as in the Mediterranean coast (Delgado et al., 1999; Pergent et al., 1999). Fish pens
have been demonstrated to cause seagrass loss (Delgado et al., 1999; Pergent et al., 1999). Extensive and
intensive aquaculture developments are expanding
worldwide, increasing the risk of more loss.
X. Summary
The nine species of Posidonia occur in two separate
biogeographic regions: the Mediterranean Sea and
the temperate southern coasts of Australia. Probably separated during the Late Eocene, Mediterranean and Australian species of Posidonia show
large divergences in the DNA sequences and in
shoot phenology and growth characteristics. They
are all perennial plants, with linear leaves attached
to a leaf-sheath which remains underground after
the leaf-blade has been shed. The genus consists of
large seagrasses with long leaves, and low rates of
leaf and shoot turnover compared to smaller, fast
growing seagrasses. They are monoecious, and have
hermaphrodite inflorescences without a perianth.
They inhabit exposed to moderately sheltered areas, in nutrient-poor waters with low tidal ranges.
They colonize a great range of depths (0–45 m) and
can settle on fine sand to rocky substrate. Species
of Posidonia have high biomasses, with distinct seasonal variations in productivity and are influenced by
light, temperature, nutrients, and water movement.
Despite their high biomass, species of Posidonia appear to be a minor food source, as direct grazing is
relatively unimportant but the presence of Posidonia can greatly alter species diversity and food webs
by the provision of substrata for other organisms to
settle and grow on.
Posidonia meadows are regressing in many regions as a direct result of anthropogenic activities.
Pollution and nutrient enrichment have been linked
to impacts such as overgrazing, shading of seagrass
leaves by excessive growth of epiphytic algae or phytoplankton. Deleterious effects are often difficult to
detect in time: the health status of the interconnected
Posidonia shoots, generally expressed in terms of
biomass and production, does not directly reflect the
environmental degradation, and by the time Posidonia is showing signs of regression, the rest of the
ecosystem is already largely affected. The transplantation of these long-live species is slow and costly,
and it is wiser to ensure their preservation by protection, rather than by the difficult process of ecosystem
restoration.
References
Abel KM and Drew EA (1989) Carbon metabolism. In: Larkum
AWD, McComb AJ and Shepherd SA (eds) Biology of Seagrasses, pp 760–796. Elsevier, Amsterdam
Agostini S, Desjobert JM and Pergent G (1998) Distribution
of phenolic compounds in the seagrass Posidonia oceanica.
Phytochemistry 48: 611–617
Alcoverro T, Duarte CM and Romero J (1995) Annual growth
dynamics of Posidonia oceanica: Contribution of large-scale
401
region supports agriculture and mariculture as well
as wild fisheries, industry, and navigation.
Monitoring strategies have been recently proposed to control and conserve meadow habitats (e.g.
Moreno et al., 2001). Seagrass meadows are a priority habitat under the European Union Species and
Habitats Directive (H&SD, 92/43/EEC).
The protection and conservation is of primary importance, but the replanting of Posidonia shoots is
slow and difficult. Survival of transplants is low in
the Mediterranean (Molenaar and Meinesz, 1995;
Molenaar et al., 2000), and only about 40% survive
in southern Australia (Lord et al., 1999). Transplantation is accompanied by modifications of biometry,
and modifications of C, N, and P content, which reflect weakness of the strategy (Lepoint et al., 2004a).
One year after transplanting, shoots are still unable to satisfy their nutrient demand (Gobert, 2004;
Lepoint et al., 2004; Vangeluwe et al., 2004).
The introduction of exotic marine organisms,
from accidental release, vessel ballast water, hull
fouling, and aquaculture, remains an area of concern
(Boudouresque and Verlaque, 2002; Duarte et al. in
press; Ralph et al. Chapter 24), particularly where the
introduced species are competitors for soft bottom
substratum such as the algae Caulerpa taxifolia, and
Caulerpa racemosa in the Mediterranean (Meinesz
et al., 1993; Deville and Verlaque, 1995; Ceccherelli
and Cinelli, 1999) and the fan worm Sabella spallanzanii in southern Australia (Lemmens et al., 1996).
Aquaculture of fish and algal biomass has been
shown to produce major environmental impacts, particularly due to shading, eutrophication, and sediment deterioration through excess organic inputs
(Seymour and Bergheim, 1991; Shireman and Cichra, 1994; Dosdat et al., 1995; Holmer et al., 2001).
The effects of fish farms and other aquaculture developments are of concern as areas of productive
seagrass habitats are often targeted for such developments, such as in the Mediterranean coast (Delgado et al., 1999; Pergent et al., 1999). Fish pens
have been demonstrated to cause seagrass loss (Delgado et al., 1999; Pergent et al., 1999). Extensive and
intensive aquaculture developments are expanding
worldwide, increasing the risk of more loss.
X. Summary
The nine species of Posidonia occur in two separate
biogeographic regions: the Mediterranean Sea and
the temperate southern coasts of Australia. Probably separated during the Late Eocene, Mediterranean and Australian species of Posidonia show
large divergences in the DNA sequences and in
shoot phenology and growth characteristics. They
are all perennial plants, with linear leaves attached
to a leaf-sheath which remains underground after
the leaf-blade has been shed. The genus consists of
large seagrasses with long leaves, and low rates of
leaf and shoot turnover compared to smaller, fast
growing seagrasses. They are monoecious, and have
hermaphrodite inflorescences without a perianth.
They inhabit exposed to moderately sheltered areas, in nutrient-poor waters with low tidal ranges.
They colonize a great range of depths (0–45 m) and
can settle on fine sand to rocky substrate. Species
of Posidonia have high biomasses, with distinct seasonal variations in productivity and are influenced by
light, temperature, nutrients, and water movement.
Despite their high biomass, species of Posidonia appear to be a minor food source, as direct grazing is
relatively unimportant but the presence of Posidonia can greatly alter species diversity and food webs
by the provision of substrata for other organisms to
settle and grow on.
Posidonia meadows are regressing in many regions as a direct result of anthropogenic activities.
Pollution and nutrient enrichment have been linked
to impacts such as overgrazing, shading of seagrass
leaves by excessive growth of epiphytic algae or phytoplankton. Deleterious effects are often difficult to
detect in time: the health status of the interconnected
Posidonia shoots, generally expressed in terms of
biomass and production, does not directly reflect the
environmental degradation, and by the time Posidonia is showing signs of regression, the rest of the
ecosystem is already largely affected. The transplantation of these long-live species is slow and costly,
and it is wiser to ensure their preservation by protection, rather than by the difficult process of ecosystem
restoration.
References
Abel KM and Drew EA (1989) Carbon metabolism. In: Larkum
AWD, McComb AJ and Shepherd SA (eds) Biology of Seagrasses, pp 760–796. Elsevier, Amsterdam
Agostini S, Desjobert JM and Pergent G (1998) Distribution
of phenolic compounds in the seagrass Posidonia oceanica.
Phytochemistry 48: 611–617
Alcoverro T, Duarte CM and Romero J (1995) Annual growth
dynamics of Posidonia oceanica: Contribution of large-scale