seasonal variations (Mateo-Ramírez and García Raso 2012; Mateo-Ramírez et al.
2018).
Like the midlittoral rocky shore, infralittoral hard bottoms including the community of photophilous algae can theoretically enter the loose concept of Habitat 1170
“Reefs” from the EU Habitats Directive. Because it is so extensive, this habitat is
well represented in most of the existing marine protected areas. Threats and pressures are many because of the accessibility of this habitat and include illegal
harvesting as well as trampling and oil spills.
9.4.2 Posidonia oceanica
The Mediterranean angiosperm Posidonia oceanica is the largest of the marine
phanerogams found in the Alboran Sea and the most outstanding as for habitat
engineering. It is very demanding in terms of ecological requirements and does not
tolerate large variations of salinity; therefore, it is not found in brackish or
hyperhaline lagoons, neither near river mouths. It is also very sensitive to eutrophication and to most of the pollutants and also does not tolerate high sedimentation
rates (Boudouresque et al. 2006; Templado et al. 2012 and references therein). It can
be considered, therefore, an indicator of clear, well-oxygenated and pollution-free
waters. Posidonia meadows occupy a wide bathymetric range (from 0 to more than
30 m deep), which implies that it occurs through a gradient in various biological
factors and hydrological parameters, such as wave action, light and temperature.
Posidonia meadows are a complex ecosystem, in which the leaf stratum and the
lattice of rhizomes have very different characteristics and associated fauna. The leaf
stratum is a relatively unstable habitat in which the leaves are continually renewed
and are subjected to wave action and to the grazing action of some species, such as
the salema (Sarpa salpa). The stratum of rhizomes is more stable, albeit illumination
may vary according to leaf growth and presents greater complexity.
Posidonia may grow both on sedimentary and rocky substrates, but when
installed on soft bottoms, the rhizome stratum forms a rigid structure which provides
the features of a hard bottom. When the meadow is installed on sandy bottoms, the
rhizomes may be mostly buried and leave little space for animals; otherwise the
rhizomes leave an intricate network of cavities, populated by the sciaphilous species
characteristic of hard substrates. The rhizome stratum grows at very slow rates
(10 cm–1 m per century) and may build up to several metres in thickness in some
parts of the Mediterranean (Boudouresque et al. 2006).
Whereas extensive Posidonia beds are found in most of the Mediterranean Sea
(see Giakoumi et al. 2013; Telesca et al. 2015), the occurrences in the Alboran Sea
are patchy (Junta de Andalucía 2008–2019; Aranda and Otero 2014). On the
northern shore, the most extensive meadows are found along the eastern coast of
Almería, in the Cabo de Gata-Níjar Natural Park (Fig. 9.9) and in several Special
Areas of Conservation (SACs) nearby, like those of Fondos Marinos de Punta
Entinas-Sabinar and that of Fondos Marinos del Levante Almeriense. A small
304
J. L. Rueda et al.
2018).
Like the midlittoral rocky shore, infralittoral hard bottoms including the community of photophilous algae can theoretically enter the loose concept of Habitat 1170
“Reefs” from the EU Habitats Directive. Because it is so extensive, this habitat is
well represented in most of the existing marine protected areas. Threats and pressures are many because of the accessibility of this habitat and include illegal
harvesting as well as trampling and oil spills.
9.4.2 Posidonia oceanica
The Mediterranean angiosperm Posidonia oceanica is the largest of the marine
phanerogams found in the Alboran Sea and the most outstanding as for habitat
engineering. It is very demanding in terms of ecological requirements and does not
tolerate large variations of salinity; therefore, it is not found in brackish or
hyperhaline lagoons, neither near river mouths. It is also very sensitive to eutrophication and to most of the pollutants and also does not tolerate high sedimentation
rates (Boudouresque et al. 2006; Templado et al. 2012 and references therein). It can
be considered, therefore, an indicator of clear, well-oxygenated and pollution-free
waters. Posidonia meadows occupy a wide bathymetric range (from 0 to more than
30 m deep), which implies that it occurs through a gradient in various biological
factors and hydrological parameters, such as wave action, light and temperature.
Posidonia meadows are a complex ecosystem, in which the leaf stratum and the
lattice of rhizomes have very different characteristics and associated fauna. The leaf
stratum is a relatively unstable habitat in which the leaves are continually renewed
and are subjected to wave action and to the grazing action of some species, such as
the salema (Sarpa salpa). The stratum of rhizomes is more stable, albeit illumination
may vary according to leaf growth and presents greater complexity.
Posidonia may grow both on sedimentary and rocky substrates, but when
installed on soft bottoms, the rhizome stratum forms a rigid structure which provides
the features of a hard bottom. When the meadow is installed on sandy bottoms, the
rhizomes may be mostly buried and leave little space for animals; otherwise the
rhizomes leave an intricate network of cavities, populated by the sciaphilous species
characteristic of hard substrates. The rhizome stratum grows at very slow rates
(10 cm–1 m per century) and may build up to several metres in thickness in some
parts of the Mediterranean (Boudouresque et al. 2006).
Whereas extensive Posidonia beds are found in most of the Mediterranean Sea
(see Giakoumi et al. 2013; Telesca et al. 2015), the occurrences in the Alboran Sea
are patchy (Junta de Andalucía 2008–2019; Aranda and Otero 2014). On the
northern shore, the most extensive meadows are found along the eastern coast of
Almería, in the Cabo de Gata-Níjar Natural Park (Fig. 9.9) and in several Special
Areas of Conservation (SACs) nearby, like those of Fondos Marinos de Punta
Entinas-Sabinar and that of Fondos Marinos del Levante Almeriense. A small
304
J. L. Rueda et al.