of the Spanish populations south of the Ebro Delta, including the Alboran Sea (see
Chap. 10 of this book). Pinna rudis, a similar but smaller species that usually lives in
hard substrates, is also frequently observed over Posidonia rhizomes, particularly in
the western part, and has not been affected by this massive mortality event.
In addition to the communities associated with leaves and rhizomes, there are a
number of mobile species that move through the meadow in search of shelter or
forage for food. These are mostly fish (e.g. Gobius spp., Symphodus spp., Serranus
scriba, S. cabrilla, Coris julis, Sarpa salpa) but also crustaceans and cephalopods,
such as the cuttlefish Sepia officinalis (García Raso et al. 1992; Luque and Templado
2004).
There is definitely an interaction and connectivity between the Posidonia community and surrounding habitats, although the rhizome (due to its morphological
characteristics, complexity and protection capacity) seems more stable. This
exchange may minimize the negative effect that the fragmentation of Posidonia
meadows (which is frequent in a large part of the Alboran Sea, near the western limit
of its distribution) could cause on the animal community (Luque and Templado
2004; Urra et al. 2013b; Mateo-Ramírez et al. 2015). The seasonal dynamics of the
associated fauna is driven by the annual variability of the dominant species, with
greater abundance and specific richness observed in the spring and summer months
in the case of molluscs (Urra et al. 2013b) and in autumn for the decapod crustaceans
(Mateo-Ramírez et al. 2015), due to reproductive events.
Mesophyllum alternans is a coralline alga which takes the form of rather large
(up to 20 cm) rosettes and is mostly associated with the rhizomes of P. oceanica.
This alga encloses a complex network of cavities, which provides shelter to a rich
and varied animal community and therefore enhances the biodiversity and the value
of the Posidonia meadow in the Alboran Sea (Hergueta and Salas 1986; García Raso
and Fernández Muñoz 1987; Fernández Muñoz and García Raso 1987; López de la
Rosa and García Raso 1992; García Raso et al. 1996). The enclosed fauna is
typically composed by gastropods, such as Alvania nestaresi and Chauvetia
mamillata, bivalves such as Hiatella arctica and Striarca lactea and decapods
such as Alpheus dentipes, Pilumnus hirtellus, Pisidia longimana, Athanas nitescens
and Cestopagurus timidus (Luque and Templado 2004). Sponges such as Sycon spp.
and Leuconia sp.; the polychaetes Platynereis dumerilii, Ceratonereis costae and
Syllis gracilis (Luque and Templado 2004); the pycnogonids Achelia langi and
Tanystylum conirostre (Munilla 1991); and the echinoderm Amphipholis squamata,
among many others, are also common (Luque and Templado 2004). In addition,
many juveniles of larger species find refuge in these structures, such as the sea
urchins Paracentrotus lividus and Arbacia lixula. Some species, such as the excavating sponge Cliona viridis, perforate the concretions, while others such as the
vermetid Thylacodes arenarius contribute to the growth of these structures. The
mobile species, in any case, move between the rhizomes and the Mesophyllum
concretions so that both communities are quite similar.
Posidonia beds are the only accurately defined marine habitat in the EU Habitats
Directive and, fortunately, are treated therein as priority habitat “1120* Posidonia
beds (Posidonion oceanicae)” (Díaz Almela and Marbà 2009) which requires that at
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J. L. Rueda et al.
Chap. 10 of this book). Pinna rudis, a similar but smaller species that usually lives in
hard substrates, is also frequently observed over Posidonia rhizomes, particularly in
the western part, and has not been affected by this massive mortality event.
In addition to the communities associated with leaves and rhizomes, there are a
number of mobile species that move through the meadow in search of shelter or
forage for food. These are mostly fish (e.g. Gobius spp., Symphodus spp., Serranus
scriba, S. cabrilla, Coris julis, Sarpa salpa) but also crustaceans and cephalopods,
such as the cuttlefish Sepia officinalis (García Raso et al. 1992; Luque and Templado
2004).
There is definitely an interaction and connectivity between the Posidonia community and surrounding habitats, although the rhizome (due to its morphological
characteristics, complexity and protection capacity) seems more stable. This
exchange may minimize the negative effect that the fragmentation of Posidonia
meadows (which is frequent in a large part of the Alboran Sea, near the western limit
of its distribution) could cause on the animal community (Luque and Templado
2004; Urra et al. 2013b; Mateo-Ramírez et al. 2015). The seasonal dynamics of the
associated fauna is driven by the annual variability of the dominant species, with
greater abundance and specific richness observed in the spring and summer months
in the case of molluscs (Urra et al. 2013b) and in autumn for the decapod crustaceans
(Mateo-Ramírez et al. 2015), due to reproductive events.
Mesophyllum alternans is a coralline alga which takes the form of rather large
(up to 20 cm) rosettes and is mostly associated with the rhizomes of P. oceanica.
This alga encloses a complex network of cavities, which provides shelter to a rich
and varied animal community and therefore enhances the biodiversity and the value
of the Posidonia meadow in the Alboran Sea (Hergueta and Salas 1986; García Raso
and Fernández Muñoz 1987; Fernández Muñoz and García Raso 1987; López de la
Rosa and García Raso 1992; García Raso et al. 1996). The enclosed fauna is
typically composed by gastropods, such as Alvania nestaresi and Chauvetia
mamillata, bivalves such as Hiatella arctica and Striarca lactea and decapods
such as Alpheus dentipes, Pilumnus hirtellus, Pisidia longimana, Athanas nitescens
and Cestopagurus timidus (Luque and Templado 2004). Sponges such as Sycon spp.
and Leuconia sp.; the polychaetes Platynereis dumerilii, Ceratonereis costae and
Syllis gracilis (Luque and Templado 2004); the pycnogonids Achelia langi and
Tanystylum conirostre (Munilla 1991); and the echinoderm Amphipholis squamata,
among many others, are also common (Luque and Templado 2004). In addition,
many juveniles of larger species find refuge in these structures, such as the sea
urchins Paracentrotus lividus and Arbacia lixula. Some species, such as the excavating sponge Cliona viridis, perforate the concretions, while others such as the
vermetid Thylacodes arenarius contribute to the growth of these structures. The
mobile species, in any case, move between the rhizomes and the Mesophyllum
concretions so that both communities are quite similar.
Posidonia beds are the only accurately defined marine habitat in the EU Habitats
Directive and, fortunately, are treated therein as priority habitat “1120* Posidonia
beds (Posidonion oceanicae)” (Díaz Almela and Marbà 2009) which requires that at
308
J. L. Rueda et al.