The flora that seagrass meadows host is similar to that of the nearby hard
substrates, but there are many organisms in the foliar stratum, where algae are the
most important component of the epiphytes that cover the leaves. Among the
seaweeds that colonize the leaves of P. oceanica are small coralline algae such as
Pneophyllum fragile, Hydrolithon farinosum, and Titanoderma pustulatum
(Templado et al. 2004). These algae are pioneers in the colonization of the leaves
and can become dominant, covering more than 40% of the surface. The erect
seaweeds colonize the leaves later and are dominant in the late phases until the
excess of epiphytes causes the loss of the leaves. Among these algae are Giraudya
sphacelarioides, Cladosiphon cylindricus, Sphacelaria cirrosa, Dictyota linearis,
Ectocarpus siliculosus, Acrochaetium daviesii, Stylonema alsidii, Ceramium
flaccidum, Dasya corymbifera, and Cladophora albida (Templado et al. 2004). In
the stratum of rhizomes, a shadier environment, there are very abundant species of
the genus Peyssonnelia, especially P. rubra and P. squamaria, and other species
such as Jania rubens, Valonia utricularis, and Flabellia petiolata, among many
others. However, the most important alga in the rhizomes is Mesophyllum alternans
(in the literature often as M. lichenoides), a red alga that forms concretions of about
40 cm in diameter and that can reach up to 80 cm and that are very characteristics of
the meadows of P. oceanica from the Alboran Sea (Junta de Andalucía 2012). These
concretions are very interesting because they provide shelter to an abundant microfauna of mollusks and crustaceans and support other rhodophytes such as Amphiroa
rigida, Jania rubens, Peyssonnelia spp., etc. (Hergueta et al. 2004).
8.4.4 Circalittoral Zone
The progressive attenuation of solar irradiance determines the lower limit of the
upper zone. It is a gradual attenuation, so changes do not occur abruptly and a clear
boundary with the infralittoral is not always present. Different biological indicators
are considered to establish the border between both areas, such as the distribution
limit of seagrasses, the substitution of photophilic species for sciaphilous ones (e.g.,
Halopteris scoparia for Halopteris filicina), or the presence of populations of deepwater species such as Cystoseira zosteroides.
The community of hard bottoms in the circalittoral zone is called the
coralligenous community. The depth at which it is found provides great stability in
terms of hydrodynamism and temperature. The coralligenous community is structured in several strata, but the floristic component is restricted to the basal layer and
is composed of species of red calcareous algae. These algae have a structural role of
great importance as generators of microhabitats that make possible the complexity
and diversity of this community (Ballesteros 2006). The coralligenous is a very
heterogeneous community and is considered among those that host the greatest
biodiversity in the Mediterranean, next to the Posidonia oceanica meadows
(Gofas et al. 2014). Among the corallinaceous species are Mesophyllum alternans,
Lithophyllum incrustans or L. stictaeforme, several species of Peyssonnelia, and
264
A. Flores-Moya et al.
substrates, but there are many organisms in the foliar stratum, where algae are the
most important component of the epiphytes that cover the leaves. Among the
seaweeds that colonize the leaves of P. oceanica are small coralline algae such as
Pneophyllum fragile, Hydrolithon farinosum, and Titanoderma pustulatum
(Templado et al. 2004). These algae are pioneers in the colonization of the leaves
and can become dominant, covering more than 40% of the surface. The erect
seaweeds colonize the leaves later and are dominant in the late phases until the
excess of epiphytes causes the loss of the leaves. Among these algae are Giraudya
sphacelarioides, Cladosiphon cylindricus, Sphacelaria cirrosa, Dictyota linearis,
Ectocarpus siliculosus, Acrochaetium daviesii, Stylonema alsidii, Ceramium
flaccidum, Dasya corymbifera, and Cladophora albida (Templado et al. 2004). In
the stratum of rhizomes, a shadier environment, there are very abundant species of
the genus Peyssonnelia, especially P. rubra and P. squamaria, and other species
such as Jania rubens, Valonia utricularis, and Flabellia petiolata, among many
others. However, the most important alga in the rhizomes is Mesophyllum alternans
(in the literature often as M. lichenoides), a red alga that forms concretions of about
40 cm in diameter and that can reach up to 80 cm and that are very characteristics of
the meadows of P. oceanica from the Alboran Sea (Junta de Andalucía 2012). These
concretions are very interesting because they provide shelter to an abundant microfauna of mollusks and crustaceans and support other rhodophytes such as Amphiroa
rigida, Jania rubens, Peyssonnelia spp., etc. (Hergueta et al. 2004).
8.4.4 Circalittoral Zone
The progressive attenuation of solar irradiance determines the lower limit of the
upper zone. It is a gradual attenuation, so changes do not occur abruptly and a clear
boundary with the infralittoral is not always present. Different biological indicators
are considered to establish the border between both areas, such as the distribution
limit of seagrasses, the substitution of photophilic species for sciaphilous ones (e.g.,
Halopteris scoparia for Halopteris filicina), or the presence of populations of deepwater species such as Cystoseira zosteroides.
The community of hard bottoms in the circalittoral zone is called the
coralligenous community. The depth at which it is found provides great stability in
terms of hydrodynamism and temperature. The coralligenous community is structured in several strata, but the floristic component is restricted to the basal layer and
is composed of species of red calcareous algae. These algae have a structural role of
great importance as generators of microhabitats that make possible the complexity
and diversity of this community (Ballesteros 2006). The coralligenous is a very
heterogeneous community and is considered among those that host the greatest
biodiversity in the Mediterranean, next to the Posidonia oceanica meadows
(Gofas et al. 2014). Among the corallinaceous species are Mesophyllum alternans,
Lithophyllum incrustans or L. stictaeforme, several species of Peyssonnelia, and
264
A. Flores-Moya et al.